Chemical Reactions and Compounds Practice Questions — Armed Services Vocational Aptitude Battery (ASVAB) — Page 2

Question 21Question →

In an acid-base neutralization reaction, aqueous hydrochloric acid ( $\text{HCl}$ ) mixes with aqueous sodium hydroxide ( $\text{NaOH}$ ) to produce table salt ( $\text{NaCl}$ ) and one neutral compound. What is the chemical formula of the missing product in the balanced reaction below?

Fill in the blanks below

\text{HCl} + \text{NaOH} \rightarrow \text{NaCl} +

Show answer & explanation

Answer

Water (

H_2O

)

In a neutralization reaction between an acid and a base, hydrogen ions (

H^+

) from the acid combine with hydroxide ions (

OH^-

) from the base to produce water (

H_2O

). The remaining sodium (

Na^+

) and chloride (

Cl^-

) ions form the salt sodium chloride (

NaCl

). Therefore, the missing product that balances the equation is

H_2O

.

Step-by-Step Solution

1

Identify the characteristic reaction type and components.

Hydrochloric acid (

HCl

) is an acid and sodium hydroxide (

NaOH

) is a base, reacting in a classic neutralization reaction.

An acid and a base neutralize each other to produce a salt (

NaCl

) and water.

2

Apply the law of conservation of mass to balance the atoms.

The reactants contain 2 hydrogen (

H

) atoms, 1 chlorine (

Cl

) atom, 1 sodium (

Na

) atom, and 1 oxygen (

O

) atom. Subtracting the sodium and chlorine in

NaCl

leaves 2 hydrogen atoms and 1 oxygen atom, which combine to form

H_2O

.

Atoms cannot be created or destroyed in a chemical reaction; all reactant atoms must appear in the products.

Key Concept

Acid-Base Neutralization and Law of Conservation of Mass

Estimated Time:45s

Question 22Question →

In an industrial chemical synthesis process, methane gas ( $\text{CH}_4$ ) reacts with high-temperature steam ( $\text{H}_2\text{O}$ ) to yield carbon monoxide ( $\text{CO}$ ) and hydrogen gas ( $\text{H}_2$ ) according to the following chemical equation:

\text{CH}_4 + \text{H}_2\text{O} \rightarrow \text{CO} + \underline{\quad ? \quad}\text{H}_2

What numerical coefficient must be placed in front of $\text{H}_2$ to balance the equation?

2

6

3

4

Show answer & explanation

Answer: 3

Answer

The numerical coefficient that balances the equation is 3.

The reactant side has a total of 6 hydrogen atoms: 4 from methane (

\text{CH}_4

) and 2 from steam (

\text{H}_2\text{O}

). Since molecular hydrogen gas is diatomic (

\text{H}_2

), a coefficient of 3 provides

3 \times 2 = 6

hydrogen atoms, successfully satisfying the Law of Conservation of Mass while leaving carbon and oxygen balanced at 1 atom each on both sides.

Step-by-Step Solution

1

Tally the number of each type of atom on the reactant side of the equation.

Reactants: 1 Carbon atom (from

\text{CH}_4

), 6 Hydrogen atoms (4 from

\text{CH}_4

plus 2 from

\text{H}_2\text{O}

), and 1 Oxygen atom (from

\text{H}_2\text{O}

).

According to the Law of Conservation of Mass, atoms cannot be created or destroyed, so total reactant atoms must equal total product atoms.

2

Tally the fixed atoms on the product side.

Products: 1 Carbon atom (in

\text{CO}

) and 1 Oxygen atom (in

\text{CO}

). Carbon and oxygen are already balanced (1 of each on both sides).

Identifies which elements are already balanced so attention can be directed to the unbalanced element.

3

Determine the required coefficient for diatomic hydrogen (

\text{H}_2

) to balance hydrogen.

To supply 6 hydrogen atoms using diatomic

\text{H}_2

molecules:

6 \div 2 = 3

.

Multiplying the coefficient 3 by the subscript 2 yields 6 hydrogen atoms, balancing the equation.

Key Concept

Balancing Chemical Equations and Conservation of Mass

Estimated Time:1m 0s

Question 23Question →

When methane gas ( $\text{CH}_4$ ) burns in the presence of oxygen gas ( $\text{O}_2$ ), it reacts to produce carbon dioxide ( $\text{CO}_2$ ) and water vapor ( $\text{H}_2\text{O}$ ). Which of the following statements correctly describes what happens to the atoms during this chemical reaction?

The molecules change their physical state without breaking or forming any chemical bonds.

The existing atoms break their original bonds and rearrange to form new chemical compounds.

The reactant atoms are destroyed during combustion and replaced by newly created product atoms.

The individual carbon and hydrogen atoms change their atomic numbers into different elements.

Show answer & explanation

Answer: The existing atoms break their original bonds and rearrange to form new chemical compounds.

Answer

The existing atoms break their original bonds and rearrange to form new chemical compounds.

In a chemical reaction, the original chemical bonds between reactant atoms break, and the atoms rearrange to form new bonds and produce distinct substances without creating or destroying any atoms.

Step-by-Step Solution

1

Identify the nature of the process described in the prompt.

The combustion of methane with oxygen is a chemical reaction that generates new substances (

\text{CO}_2

and

\text{H}_2\text{O}

).

A chemical reaction involves a change in chemical identity and composition, unlike a simple phase change.

2

Apply the principles of atomic theory and the Law of Conservation of Mass to the reaction.

The total number and identity of each atom remain constant, but the chemical bonds holding them together break and reform into new molecular structures.

Chemical reactions involve the rearrangement of valence electrons and chemical bonds between atoms, not the destruction or elemental transformation of atoms.

Key Concept

During a chemical reaction, existing chemical bonds are broken and atoms rearrange into new combinations to form different chemical compounds while conserving all atoms.

Estimated Time:45s

Question 24Question →

Read the chemical reaction scenario below and fill in the blanks with the correct numbers or terms.

Fill in the blanks below

During the complete combustion of butane (

C_4H_{10}

), the hydrocarbon reacts with oxygen gas (

O_2

) to produce carbon dioxide (

CO_2

) and water vapor (

H_2O

). When this chemical equation is balanced using the smallest possible whole numbers, the coefficient for oxygen (

O_2

) is and the sum of all coefficients in the balanced equation is . Furthermore, because this process releases net thermal energy to its surroundings, it is thermodynamically classified as an reaction.

Show answer & explanation

Answer

The balanced coefficient for oxygen is 13, the sum of all coefficients is 33, and the reaction is exothermic.

Balancing the complete combustion of butane requires compensating for an odd number of oxygen atoms on the product side by doubling all coefficients. This transforms the intermediate equation (

C_4H_{10} + 6.5O_2 \rightarrow 4CO_2 + 5H_2O

) into the proper whole-number equation (

2C_4H_{10} + 13O_2 \rightarrow 8CO_2 + 10H_2O

). The resulting oxygen coefficient is 13, and the total sum of coefficients is 2 + 13 + 8 + 10 = 33. Because the combustion process releases net thermal energy, it is classified as an exothermic reaction.

Step-by-Step Solution

1

Write the unbalanced skeletal equation for the combustion reaction.

C_4H_{10} + O_2 \rightarrow CO_2 + H_2O

Establishes the chemical formulas for all reactants and products before applying the law of conservation of mass.

2

Balance the carbon (C) and hydrogen (H) atoms first.

C_4H_{10} + O_2 \rightarrow 4CO_2 + 5H_2O

There are 4 carbons and 10 hydrogens in a butane molecule, requiring 4 molecules of carbon dioxide and 5 molecules of water to balance those elements.

3

Count the oxygen (O) atoms on the product side to determine the required oxygen on the reactant side.

Products have

(4 \times 2) + (5 \times 1) = 13

oxygen atoms. The reactants need

\frac{13}{2}

O_2

molecules.

Oxygen appears in only one reactant but multiple products, making it most efficient to balance last.

4

Multiply the entire equation by 2 to achieve the smallest whole-number coefficients.

2C_4H_{10} + 13O_2 \rightarrow 8CO_2 + 10H_2O

Standard chemical equations require the lowest possible whole-number coefficients, eliminating the fractional 6.5.

5

Identify the coefficient for oxygen and calculate the total sum of all coefficients.

Oxygen coefficient = 13. Sum =

2 + 13 + 8 + 10 = 33

.

This directly answers the first two blanks of the prompt based on the fully balanced equation.

6

Classify the reaction type based on its thermal energy transfer.

Exothermic.

Combustion reactions release heat energy into their surroundings, which is the definition of an exothermic process.

Key Concept

Advanced Stoichiometry and Thermochemistry

Question 25Question →

When an iron nail is exposed to moist air over several weeks, it reacts with oxygen gas to form iron(III) oxide (rust), as represented by the balanced equation $4\text{Fe} + 3\text{O}_2 \rightarrow 2\text{Fe}_2\text{O}_3$ . Which of the following statements correctly explains why this process is classified as a chemical change?

The iron metal merely undergoes a state change from solid to liquid due to environmental humidity.

The iron nail dissolves reversibly in atmospheric water vapor without forming any new chemical bonds.

New chemical bonds are formed between iron and oxygen atoms, producing a substance with different chemical properties.

The chemical formula subscripts of the elemental reactants change during the reaction to force the equation to balance.

Show answer & explanation

Answer: New chemical bonds are formed between iron and oxygen atoms, producing a substance with different chemical properties.

Answer

New chemical bonds are formed between iron and oxygen atoms, producing a substance with different chemical properties.

The reaction produces iron(III) oxide (

\text{Fe}_2\text{O}_3

), which is a distinct compound with chemical and physical properties entirely different from elemental iron and gaseous oxygen. Because chemical bonds are broken and new bonds are formed, the process is a chemical change.

Step-by-Step Solution

1

Analyze the reactants and products in the reaction

4\text{Fe} + 3\text{O}_2 \rightarrow 2\text{Fe}_2\text{O}_3

.

Elemental iron (

\text{Fe}

) and oxygen gas (

\text{O}_2

) react to produce the compound iron(III) oxide (

\text{Fe}_2\text{O}_3

).

Determining the chemical formulas reveals whether original substances underwent composition changes.

2

Distinguish between a physical change and a chemical change.

Physical changes alter appearance or physical state without changing chemical identity, whereas chemical changes form new chemical bonds and new substances.

Rust possesses distinct chemical reactivity, color, and magnetic properties compared to metallic iron and oxygen gas.

3

Identify the statement matching the definition of a chemical change.

The formation of new bonds producing a compound with distinct properties defines the reaction as a chemical change.

This directly demonstrates the fundamental principle of chemical reactions.

Key Concept

Chemical change versus physical change and compound formation

Estimated Time:1m 0s

Question 26Question →

When solid zinc metal is immersed in hydrochloric acid, a single displacement reaction occurs that produces aqueous zinc chloride and hydrogen gas. Based on the law of conservation of mass, what stoichiometric coefficient and chemical formula correctly complete the balanced chemical equation below?

Fill in the blanks below

$\text{Zn} + \text{HCl} \rightarrow \text{ZnCl}_2 + $

Show answer & explanation

Answer

The balanced chemical equation is completed by placing a coefficient of 2 in front of HCl and identifying H₂ (hydrogen gas) as the missing diatomic product.

In a single replacement reaction between zinc and hydrochloric acid, zinc displaces hydrogen to form zinc chloride (

\text{ZnCl}_2

) and diatomic hydrogen gas (

\text{H}_2

). To balance the

2

chlorine atoms and

2

hydrogen atoms present in the products, a coefficient of

2

must precede

\text{HCl}

on the reactant side.

Step-by-Step Solution

1

Determine the identity of the missing product from the chemical reaction description

The reaction produces zinc chloride (

\text{ZnCl}_2

) and diatomic hydrogen gas (

\text{H}_2

).

When a reactive metal displaces hydrogen from an acid in a single replacement reaction, hydrogen is liberated as diatomic gas molecules.

2

Count the number of each type of atom on the product side

Products contain

1

zinc (

\text{Zn}

) atom,

2

chlorine (

\text{Cl}

) atoms, and

2

hydrogen (

\text{H}

) atoms.

According to the law of conservation of mass, matter cannot be created or destroyed, so the reactant side must contain identical atom counts.

3

Balance the reactant side by determining the required coefficient for hydrochloric acid

Placing a coefficient of

2

before

\text{HCl}

yields

2

hydrogen atoms and

2

chlorine atoms.

One formula unit of

\text{Zn}

supplies

1

zinc atom, and

2

formula units of

\text{HCl}

supply the required

2

hydrogen and

2

chlorine atoms.

Key Concept

Single displacement reactions and balancing equations using the law of conservation of mass

Estimated Time:1m 0s

Question 27Question →

Chemical reactions can be grouped into distinct categories based on how atoms and ions are rearranged. Match each chemical reaction equation on the left with its correct classification type on the right. Which reaction type correctly pairs with each equation?

Click a left item, then click its matching right item

Show answer & explanation

Answer

The magnesium burning equation pairs with synthesis, hydrogen peroxide breakdown pairs with decomposition, copper reacting with silver nitrate pairs with single displacement, and silver nitrate reacting with sodium chloride pairs with double displacement.

Each chemical reaction matches its structural pattern: synthesis creates one product from multiple reactants, decomposition breaks one reactant into multiple products, single displacement involves a free element displacing an ion from a compound, and double displacement involves two ionic compounds exchanging ion partners.

Step-by-Step Solution

1

Analyze the number and structure of reactants and products for the first equation (

2\text{Mg} + \text{O}_2 \rightarrow 2\text{MgO}

).

Two elemental reactants combine into one compound (

A + B \rightarrow AB

).

This matches the definition of a synthesis (or combination) reaction.

2

Analyze the second equation (

2\text{H}_2\text{O}_2 \rightarrow 2\text{H}_2\text{O} + \text{O}_2

).

A single compound reactant yields two distinct product molecules (

AB \rightarrow A + B

).

This matches the definition of a decomposition reaction.

3

Analyze the third equation (

\text{Cu} + 2\text{AgNO}_3 \rightarrow \text{Cu(NO}_3)_2 + 2\text{Ag}

).

An uncombined element replaces an ion in a compound (

A + BC \rightarrow AC + B

).

This is characteristic of a single replacement/displacement reaction.

4

Analyze the fourth equation (

\text{AgNO}_3 + \text{NaCl} \rightarrow \text{AgCl} + \text{NaNO}_3

).

Two ionic compounds swap binding partners (

AB + CD \rightarrow AD + CB

).

This is the hallmark of a double replacement/displacement reaction.

Key Concept

Classification of Major Chemical Reaction Types

Estimated Time:1m 0s

Question 28Question →

An electric current is passed through liquid water containing a small amount of an electrolyte, producing hydrogen gas and oxygen gas according to the equation:

2\text{H}_2\text{O}\text{(l)} \rightarrow 2\text{H}_2\text{(g)} + \text{O}_2\text{(g)}

Which statement best explains why this process is classified as a chemical change rather than a physical change?

The liquid water absorbs energy and undergoes a physical phase change into water vapor.

Covalent bonds within water molecules are broken and new substances with distinct chemical properties are formed.

The total mass of the resulting gases is greater than the mass of the liquid water consumed.

Water molecules physically dissolve and separate into individual ions without forming new neutral molecules.

Show answer & explanation

Answer: Covalent bonds within water molecules are broken and new substances with distinct chemical properties are formed.

Answer

Covalent bonds within water molecules are broken and new substances with distinct chemical properties are formed.

The process is a chemical change because intramolecular covalent bonds in the reactant compound are broken, rearranging the atoms to form new elemental substances with entirely different chemical and physical properties.

Step-by-Step Solution

1

Analyze the chemical formulas of the reactants and products in the reaction equation (

2\text{H}_2\text{O} \rightarrow 2\text{H}_2 + \text{O}_2

).

Liquid water (a chemical compound) is converted into two distinct elemental gases: hydrogen and oxygen.

Determines whether the chemical identity of the starting substance is preserved or transformed.

2

Differentiate between a physical change and a chemical change at the molecular level.

The existing

\text{H}-\text{O}

covalent bonds in

\text{H}_2\text{O}

are broken, and new

\text{H}-\text{H}

and

\text{O}=\text{O}

bonds are created.

A chemical change is fundamentally defined by the rearrangement of atoms through the breaking and forming of chemical bonds to create new substances.

Key Concept

A chemical change involves breaking and forming chemical bonds to produce new substances with distinct chemical properties, in accordance with the law of conservation of mass.

Estimated Time:1m 0s

Question 29Question →

When solid baking soda (sodium bicarbonate, $NaHCO_3$ ) is added to vinegar (acetic acid, $CH_3COOH$ ), vigorous bubbling occurs as carbon dioxide gas ( $CO_2$ ), water ( $H_2O$ ), and sodium acetate ( $CH_3COONa$ ) are produced. Why is this process classified as a chemical change rather than a physical change?

The solid dissolves and undergoes a reversible state change from solid to gas.

New chemical substances with distinct molecular structures and properties are formed.

Thermal conduction causes the liquid vinegar to boil rapidly into carbon dioxide vapor.

The total mass of the resulting products increases because new atoms are created.

Show answer & explanation

Answer: New chemical substances with distinct molecular structures and properties are formed.

Answer

New chemical substances with distinct molecular structures and properties are formed.

A chemical change is characterized by the rearrangement of atoms and the formation of one or more entirely new substances with distinct physical and chemical properties, as seen with the production of carbon dioxide, water, and sodium acetate.

Step-by-Step Solution

1

Analyze the starting reactants and resulting products in the scenario.

Reactants (

NaHCO_3

and

CH_3COOH

) produce entirely new compounds (

CO_2

,

H_2O

, and

CH_3COONa

).

Identifying the formation of new chemical identities is fundamental to determining the type of change.

2

Distinguish between physical and chemical processes.

Physical changes alter only the form or state of matter without changing chemical formulas, whereas chemical changes involve the rearrangement of atoms into new chemical compounds.

The defining characteristic of a chemical change is the synthesis or decomposition of chemical bonds resulting in new substances.

Key Concept

Chemical change involves breaking and forming chemical bonds to produce new substances with different properties.

Estimated Time:1m 0s

Question 30Question →

In industrial metallurgy, solid aluminum metal reacts with oxygen gas at elevated temperatures to form solid aluminum oxide according to the unbalanced chemical equation:

\text{__}\text{Al} + 3\text{O}_2 \rightarrow 2\text{Al}_2\text{O}_3

Determine the missing stoichiometric coefficient required to balance this chemical equation and complete the statement below.

Fill in the blanks below

To satisfy the law of conservation of mass, the stoichiometric coefficient placed before

\text{Al}

must be .

Show answer & explanation

Answer

The stoichiometric coefficient for aluminum is 4.

The coefficient 4 correctly balances the equation because the product side has 2 formula units of

\text{Al}_2\text{O}_3

, containing a total of

2 \times 2 = 4

aluminum atoms. In accordance with the law of conservation of mass, matter cannot be created or destroyed in a chemical reaction, requiring 4 aluminum atoms on the reactant side (

4\text{Al} + 3\text{O}_2 \rightarrow 2\text{Al}_2\text{O}_3

).

Step-by-Step Solution

1

Count the total number of aluminum and oxygen atoms present in the products.

The product side contains

2\text{Al}_2\text{O}_3

, which has

2 \times 2 = 4

aluminum atoms and

2 \times 3 = 6

oxygen atoms.

Coefficients multiply all subscripts within a chemical formula to give total atom counts.

2

Verify oxygen atom balance on the reactant side.

The reactant side has

3\text{O}_2

, which equals

3 \times 2 = 6

oxygen atoms, perfectly matching the product side.

Verifying one element ensures that only the unknown coefficient needs adjustment.

3

Determine the coefficient for elemental aluminum on the reactant side.

Since single aluminum atoms are represented as

\text{Al}

, placing a coefficient of 4 yields

4 \times 1 = 4

aluminum atoms.

The law of conservation of mass requires the same number of each type of atom on both sides of the equation.

Key Concept

Balancing Chemical Equations via Mass Conservation

Estimated Time:1m 0s

Question 31Question →

When clear aqueous solutions of silver nitrate (

AgNO_3

) and sodium chloride (

NaCl

) are mixed, an insoluble white solid of silver chloride (

AgCl

) immediately forms and precipitates out of the solution, leaving dissolved sodium nitrate (

NaNO_3

):

AgNO_3 + NaCl \rightarrow AgCl + NaNO_3

Which type of chemical reaction is represented by this process?

Single replacement reaction

Double replacement reaction

Decomposition reaction

Physical phase change

Show answer & explanation

Answer: Double replacement reaction

Answer

Double replacement reaction

In a double replacement (or double displacement) reaction, two ionic compounds in aqueous solution exchange partner ions to form two new compounds. Here, silver cations (

Ag^+

) combine with chloride anions (

Cl^-

) to form an insoluble solid precipitate of silver chloride (

AgCl

), while sodium ions (

Na^+

) and nitrate ions (

NO_3^-

) remain in solution as sodium nitrate (

NaNO_3

).

Step-by-Step Solution

1

Analyze the reactants and products in the chemical equation.

The reaction begins with two aqueous ionic compounds, silver nitrate (

AgNO_3

) and sodium chloride (

NaCl

), and produces two distinct compounds, solid silver chloride (

AgCl

) and aqueous sodium nitrate (

NaNO_3

).

Identifying the number and chemical nature of reactant and product species is essential to determining the reaction archetype.

2

Track how the ions rearrange during the reaction.

The silver cation (

Ag^+

) switches partners from nitrate (

NO_3^-

) to chloride (

Cl^-

), while the sodium cation (

Na^+

) switches from chloride to nitrate.

Observing a mutual exchange of ion partners between two compounds confirms that an ion-exchange process has taken place.

3

Match the observed ion exchange with standard chemical reaction classifications.

A reaction of the general form

AB + CD \rightarrow AD + CB

in which two ionic compounds exchange ions to form a precipitate is classified as a double replacement (double displacement) reaction.

Classifying the reaction distinguishes it from synthesis, decomposition, single replacement, and physical state transitions.

Key Concept

Double replacement reactions occur when the cations and anions of two aqueous ionic compounds exchange places, frequently driven by the formation of an insoluble solid precipitate, a gas, or water.

Estimated Time:1m 0s

Question 32Question →

Chemical compounds are commonly identified by both everyday names and standard IUPAC chemical formulas. Match each common chemical substance on the left with its correct chemical formula and characteristic reaction property on the right.

Click a left item, then click its matching right item

Show answer & explanation

Answer

Calcium carbonate matches with

CaCO_3

(carbonate salt releasing

CO_2

), Sodium hydroxide matches with

NaOH

(strong base used in drain cleaners), Hydrochloric acid matches with

HCl

(strong acid in gastric juices), and Methane matches with

CH_4

(combustible hydrocarbon producing

CO_2

and

H_2O

).

Each substance is accurately paired with its standard chemical formula and defining chemical reaction property: calcium carbonate (

CaCO_3

) produces carbon dioxide when acidified, sodium hydroxide (

NaOH

) acts as an alkaline cleaner, hydrochloric acid (

HCl

) serves as stomach acid and an industrial pickling agent, and methane (

CH_4

) combusts cleanly to produce carbon dioxide and water.

Step-by-Step Solution

1

Identify the chemical identity and formula of limestone / calcium carbonate.

Limestone is composed of calcium (

Ca^{2+}

) and carbonate (

CO_3^{2-}

), giving the formula

CaCO_3

, which reacts with acids to form

CO_2

.

Matching common chemical names to their constituent ions and chemical behavior establishes the correct pair.

2

Identify the formula and basic nature of lye / sodium hydroxide.

Lye is sodium hydroxide (

NaOH

), a well-known strong base used in cleaning agents.

Recognizing alkali metals bonded to hydroxide ions identifies basic cleaning compounds.

3

Determine the composition and biological occurrence of muriatic acid.

Muriatic acid is an industrial name for hydrochloric acid (

HCl

), which is also secreted in the stomach to aid digestion.

Connecting mineral acid formulas to biological and commercial contexts confirms the match.

4

Classify natural gas / methane and its combustion behavior.

Methane is

CH_4

, an alkane hydrocarbon that combusts with

O_2

to generate carbon dioxide and water vapor.

Hydrocarbon oxidation is a fundamental reaction pattern in General Science.

Key Concept

Nomenclature, formulas, and fundamental chemical behaviors of common inorganic and organic compounds

Estimated Time:1m 0s

Question 33Question →

A technician working with lead-acid vehicle batteries observes several different processes in a maintenance facility. Which of the following processes represents a chemical reaction rather than a physical change?

Distilled water evaporating from an unsealed battery cell cap on a warm workbench

Solid lead terminal posts melting under high heat during terminal reshaping

Solid lead and lead dioxide reacting with sulfuric acid to produce lead sulfate during battery discharge

Water vapor in humid air condensing into liquid droplets on the cool exterior battery casing

Show answer & explanation

Answer: Solid lead and lead dioxide reacting with sulfuric acid to produce lead sulfate during battery discharge

Answer

Solid lead and lead dioxide reacting with sulfuric acid to produce lead sulfate during battery discharge

The reaction between lead, lead dioxide, and sulfuric acid during battery discharge is a chemical change because the original substances are chemically altered to form an entirely new compound, lead sulfate (

PbSO_4

), releasing electrical energy through bond reorganization.

Step-by-Step Solution

1

Differentiate between a chemical change and a physical change.

A chemical change involves the rearrangement of atoms via bond breaking and bond formation to yield new chemical substances with distinct properties. A physical change alters only physical form, shape, or state of matter while keeping the chemical composition unchanged.

Clear scientific criteria are required to evaluate the nature of each observed process.

2

Analyze the atomic and molecular changes occurring in each scenario.

Evaporating water (

H_2O_{(l)} \rightarrow H_2O_{(g)}

), melting lead (

Pb_{(s)} \rightarrow Pb_{(l)}

), and condensing water (

H_2O_{(g)} \rightarrow H_2O_{(l)}

) are all phase changes where molecular formulas remain identical. In contrast, lead-acid battery discharge involves lead (

Pb

), lead dioxide (

PbO_2

), and sulfuric acid (

H_2SO_4

) reacting to create a new chemical substance, lead sulfate (

PbSO_4

).

Determining whether chemical composition is conserved or transformed identifies the presence of a chemical reaction.

3

Identify the process that forms new chemical compounds.

The discharge of the lead-acid battery is the only process where reactants are converted into chemically distinct products.

The generation of lead sulfate (

PbSO_4

) confirms a chemical reaction.

Key Concept

Differentiating chemical reactions (which produce new substances with new chemical properties through bond breaking and formation) from physical phase changes (which preserve molecular composition).

Estimated Time:1m 0s

Question 34Question →

Complete the following statement regarding the complete combustion of methane fuel by identifying the missing compound and the stoichiometric balancing coefficient.

Fill in the blanks below

During the complete combustion of methane (

CH_4

), the fuel reacts with atmospheric oxygen (

O_2

) to produce carbon dioxide (

CO_2

) and . In the balanced chemical equation

CH_4 + \underline{\quad} O_2 \rightarrow CO_2 + 2H_2O

, the numerical coefficient required in front of

O_2

is .

Show answer & explanation

Answer

The missing product compound is water (

H_2O

), and the balancing coefficient for oxygen gas (

O_2

) is 2.

In the complete combustion of any simple hydrocarbon such as methane (

CH_4

), the products are always carbon dioxide (

CO_2

) and water (

H_2O

). To balance the equation

CH_4 + x O_2 \rightarrow CO_2 + 2H_2O

, we tally the atoms on each side. Carbon has 1 atom on both sides; hydrogen has 4 atoms on both sides (

4

in

CH_4

and

2 \times 2 = 4

in

2H_2O

). The product side contains 4 total oxygen atoms (2 from

CO_2

and 2 from

2H_2O

). Therefore,

2

molecules of diatomic oxygen (

2 O_2

) are required on the reactant side to conserve mass.

Step-by-Step Solution

1

Identify the missing chemical product containing hydrogen.

Water (

H_2O

)

Hydrocarbon combustion involves the oxidation of carbon to carbon dioxide (

CO_2

) and hydrogen to water (

H_2O

).

2

Count total oxygen atoms present in the products.

4 oxygen atoms total

The products consist of 1 molecule of

CO_2

(contributing 2 oxygen atoms) and 2 molecules of

H_2O

(contributing

2 \times 1 = 2

oxygen atoms), giving

2 + 2 = 4

oxygen atoms.

3

Determine the required coefficient for diatomic oxygen (

O_2

) on the reactant side to satisfy the law of conservation of mass.

A coefficient of 2

Since each

O_2

molecule contains 2 oxygen atoms, dividing 4 required oxygen atoms by 2 yields a stoichiometric coefficient of 2.

Key Concept

Hydrocarbon Combustion and Equation Balancing

Estimated Time:1m 0s

Question 35Question →

In aerospace manufacturing, a protective oxide layer forms when solid aluminum reacts with atmospheric oxygen gas according to the unbalanced chemical equation:

\underline{\quad}\text{Al} + 3\text{O}_2 \rightarrow 2\text{Al}_2\text{O}_3

To satisfy the Law of Conservation of Mass, what coefficient must be placed in front of $\text{Al}$ to properly balance this chemical equation?

2

1

4

6

Show answer & explanation

Answer: $4$

Answer

The coefficient required in front of

\text{Al}

is

4

.

In the chemical equation, the product side shows two formula units of aluminum oxide (

2\text{Al}_2\text{O}_3

). Multiplying the leading coefficient of

2

by the subscript of

2

for aluminum gives

2 \times 2 = 4

aluminum atoms in the products. Conserving matter requires exactly

4

aluminum atoms on the reactant side, producing the balanced equation

4\text{Al} + 3\text{O}_2 \rightarrow 2\text{Al}_2\text{O}_3

.

Step-by-Step Solution

1

Count the total number of aluminum atoms on the product side of the equation.

The product side contains

2\text{Al}_2\text{O}_3

, which has

2 \times 2 = 4

aluminum atoms.

According to the Law of Conservation of Mass, the number of atoms of each element must remain constant throughout a chemical reaction.

2

Determine the coefficient needed for aluminum on the reactant side to balance the four product aluminum atoms.

Since aluminum appears as an individual atom

\text{Al}

, a coefficient of

4

provides

4 \times 1 = 4

aluminum atoms.

Assigning a coefficient of

4

balances the equation completely:

4\text{Al} + 3\text{O}_2 \rightarrow 2\text{Al}_2\text{O}_3

, with 4 aluminum atoms and 6 oxygen atoms on each side.

Key Concept

Balancing chemical equations by applying the Law of Conservation of Mass to ensure equal numbers of each atomic species among reactants and products.

Estimated Time:1m 0s

Question 36Question →

In an industrial metal recovery process, solid aluminum reacts with an aqueous solution of copper(II) sulfate according to the unbalanced chemical equation:

\text{Al}(s) + \text{CuSO}_4(aq) \rightarrow \text{Al}_2(\text{SO}_4)_3(aq) + \text{Cu}(s)

When this equation is completely balanced using the smallest possible whole-number coefficients, what is the sum of all the stoichiometric coefficients?

4

8

9

7

Show answer & explanation

Answer: $9$

Answer

The sum of all stoichiometric coefficients in the balanced equation is

9

.

Balancing the equation requires

2

aluminum atoms and

3

copper(II) sulfate units to react to form

1

unit of aluminum sulfate and

3

copper atoms:

2\text{Al}(s) + 3\text{CuSO}_4(aq) \rightarrow 1\text{Al}_2(\text{SO}_4)_3(aq) + 3\text{Cu}(s)

. Summing all four stoichiometric coefficients gives

2 + 3 + 1 + 3 = 9

.

Step-by-Step Solution

1

Count the number of each type of atom/polyatomic ion in the unbalanced equation.

Reactants:

1\text{ Al}

,

1\text{ Cu}

,

1\text{ SO}_4^{2-}

. Products:

2\text{ Al}

,

1\text{ Cu}

,

3\text{ SO}_4^{2-}

.

Establishing initial quantities identifies which species violate the Law of Conservation of Mass.

2

Balance the polyatomic sulfate groups by placing a coefficient of

3

before

\text{CuSO}_4

.

\text{Al} + 3\text{CuSO}_4 \rightarrow \text{Al}_2(\text{SO}_4)_3 + \text{Cu}

Treating polyatomic ions as single units when they remain intact simplifies balancing.

3

Balance the aluminum and copper atoms by adding coefficients of

2

to

\text{Al}

and

3

to

\text{Cu}

.

2\text{Al} + 3\text{CuSO}_4 \rightarrow 1\text{Al}_2(\text{SO}_4)_3 + 3\text{Cu}

Ensures equal numbers of each elemental atom on both the reactant and product sides.

4

Sum all lowest whole-number coefficients, including the implicit coefficient of

1

.

2 + 3 + 1 + 3 = 9

Calculates the total coefficient sum requested in the problem.

Key Concept

Balancing chemical equations according to the Law of Conservation of Mass using lowest whole-number stoichiometric coefficients.

Estimated Time:1m 15s

Chemical Reactions and Compounds

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Answer

Step-by-Step Solution

Key Concept

Common Mistakes