Physical Science Practice Questions — Armed Services Vocational Aptitude Battery (ASVAB) — Page 8

Question 141Question →

An electric delivery van with a total mass of $2,000\text{ kg}$ travels along a straight road at a constant velocity of $15\text{ m/s}$ . The driver applies the brakes, producing a constant opposing friction force of $6,000\text{ N}$ until the vehicle comes to a complete stop. How much time does it take for the van to stop?

20\text{ seconds}

5\text{ seconds}

50\text{ seconds}

45\text{ seconds}

Show answer & explanation

Answer: $5\text{ seconds}$

Answer

The total time required for the delivery van to come to a complete stop is

5\text{ seconds}

.

According to Newton's second law (

F = ma

), the opposing braking force of

6,000\text{ N}

acting on a

2,000\text{ kg}

vehicle produces an acceleration of

a = \frac{6,000\text{ N}}{2,000\text{ kg}} = 3\text{ m/s}^2

. To bring the vehicle from

15\text{ m/s}

to rest at a rate of

3\text{ m/s}^2

, the time needed is

t = \frac{\Delta v}{a} = \frac{15\text{ m/s}}{3\text{ m/s}^2} = 5\text{ seconds}

.

Step-by-Step Solution

1

Calculate the magnitude of deceleration using Newton's second law of motion (

F = ma

).

a = \frac{F}{m} = \frac{6,000\text{ N}}{2,000\text{ kg}} = 3\text{ m/s}^2

The net opposing force applied to the known mass determines the rate at which the vehicle slows down.

2

Determine the time required to reduce the velocity from

15\text{ m/s}

to

0\text{ m/s}

using the kinematic definition of acceleration (

t = \frac{\Delta v}{a}

).

t = \frac{15\text{ m/s}}{3\text{ m/s}^2} = 5\text{ seconds}

Uniform deceleration reduces speed at a constant rate of

3\text{ m/s}

each second until rest is reached.

Key Concept

Newton's Second Law of Motion and Linear Deceleration

Estimated Time:1m 0s

Question 142Question →

An isotope of carbon has a mass number of $14$ and contains $8$ neutrons in its nucleus. What is the atomic number of this carbon atom?

22

6

8

14

Show answer & explanation

Answer: $6$

Answer

6

The atomic number represents the number of protons in an atom's nucleus. Since the mass number (

14

) is the sum of protons and neutrons, subtracting the

8

neutrons from

14

yields

6

protons, making the atomic number

6

.

Step-by-Step Solution

1

Identify the relationship between mass number, atomic number, and neutrons.

\text{Mass Number} = \text{Atomic Number (Protons)} + \text{Neutrons}

The mass number of an atom is defined as the total number of protons and neutrons in the nucleus.

2

Substitute the known values and solve for the atomic number.

\text{Atomic Number} = 14 - 8 = 6

Subtracting the

8

neutrons from the total mass number of

14

gives the number of protons, which defines the atomic number.

Key Concept

Relationship between mass number, atomic number, and subatomic particles

Estimated Time:45s

Question 143Question →

During a cold-storage maintenance procedure, a technician handles solid dry ice (solid $\text{CO}_2$ ) and observes it converting directly into carbon dioxide gas at room temperature without forming any liquid. Which term correctly describes this phase transition, and is it classified as a physical or chemical change?

Evaporation, which is a chemical change because intermolecular forces are broken to create a gas.

Sublimation, which is a physical change because the chemical identity of the substance remains unchanged.

Sublimation, which is a chemical change because the substance undergoes a complete change in state.

Condensation, which is a physical change because heat energy is absorbed during the transition.

Show answer & explanation

Answer: Sublimation, which is a physical change because the chemical identity of the substance remains unchanged.

Answer

Sublimation, which is a physical change because the chemical identity of the substance remains unchanged.

The transition directly from a solid state to a gaseous state is known as sublimation. Because the chemical composition of dry ice remains carbon dioxide (

\text{CO}_2

) throughout the process and no new chemical substances are produced, the transition is strictly a physical change.

Step-by-Step Solution

1

Identify the specific phase transition occurring from solid to gas.

The direct phase change from a solid to a gas without passing through the liquid phase is defined as sublimation.

Understanding standard phase change terminology classifies the transition correctly.

2

Classify whether the process represents a physical change or a chemical change.

Physical change.

The molecules before and after the transition remain

\text{CO}_2

. Because no chemical bonds within the molecules are formed or broken to create new substances, it is a physical change.

Key Concept

Phase Transitions and Physical vs. Chemical Changes

Estimated Time:45s

Question 144Question →

Waves are classified based on the direction of particle vibration relative to energy transport and whether they require matter to travel. Match each wave category on the left with its defining physical property on the right.

Click a left item, then click its matching right item

Show answer & explanation

Answer

Transverse wave pairs with perpendicular particle oscillation; longitudinal wave pairs with parallel particle oscillation; electromagnetic wave pairs with propagation through a vacuum; mechanical wave pairs with the requirement of a material medium.

Each term accurately links to its fundamental physical definition: transverse waves have perpendicular displacement, longitudinal waves have parallel displacement, electromagnetic waves do not need matter, and mechanical waves require a medium.

Step-by-Step Solution

1

Classify wave types by directional motion.

Transverse motion means particles move perpendicular to wave travel; longitudinal motion means particles move parallel (along the line of travel).

Wave geometric behavior is determined by the orientation of the medium's displacement relative to energy propagation.

2

Classify wave types by medium requirements.

Electromagnetic waves do not require matter to travel (can travel in a vacuum), whereas mechanical waves strictly require a solid, liquid, or gas medium.

Wave transmission mechanism depends on whether energy is carried via particle collisions (mechanical) or synchronized field oscillations (electromagnetic).

Key Concept

Wave classification by vibration direction (transverse vs. longitudinal) and medium dependence (mechanical vs. electromagnetic)

Estimated Time:45s

Question 145Question →

A conveyor system accelerates a $15\text{ kg}$ package along a straight horizontal track from an initial speed of $2\text{ m/s}$ to a final speed of $8\text{ m/s}$ in $3\text{ seconds}$ . What is the magnitude of the net horizontal force acting on the package, in newtons?

Show answer & explanation

Answer: 30

Answer

The magnitude of the net horizontal force acting on the package is

30\text{ N}

.

By finding the acceleration through

a = \frac{v_f - v_i}{t} = \frac{8 - 2}{3} = 2\text{ m/s}^2

and applying Newton's second law (

F = ma

), the resulting net force is

15\text{ kg} \times 2\text{ m/s}^2 = 30\text{ N}

.

Step-by-Step Solution

1

Determine the horizontal acceleration of the package using 1D kinematics.

a = \frac{8\text{ m/s} - 2\text{ m/s}}{3\text{ s}} = \frac{6\text{ m/s}}{3\text{ s}} = 2\text{ m/s}^2

Acceleration measures the rate of change of velocity over elapsed time (

a = \frac{\Delta v}{\Delta t}

).

2

Calculate the net force by applying Newton's second law of motion.

F_{\text{net}} = m \times a = 15\text{ kg} \times 2\text{ m/s}^2 = 30\text{ N}

Net force is directly proportional to the mass and the acceleration of the object (

F = ma

).

Key Concept

Newton's Second Law and Uniform Acceleration

Estimated Time:1m 0s

Question 146Question →

A musician tightens a guitar string, which causes the string to vibrate at a higher frequency when plucked. How does this increase in frequency change the sound that is heard?

The loudness of the sound increases.

The pitch of the sound becomes higher.

The speed of the sound wave through the surrounding air increases significantly.

The wavelength of the sound wave in the air becomes longer.

Show answer & explanation

Answer: The pitch of the sound becomes higher.

Answer

The pitch of the sound becomes higher.

The pitch of a sound is directly determined by the frequency of the sound wave. When the frequency of vibration increases, the ear perceives the sound at a higher pitch.

Step-by-Step Solution

1

Identify the acoustic property controlled by the frequency of a sound wave.

Frequency measures the number of wave cycles per second (

Hz

) and directly determines perceived pitch.

Pitch is the psychological perception of wave frequency in human hearing.

2

Determine the physical consequence of increasing the frequency of vibration.

An increase in frequency produces a higher-pitched tone.

Faster vibrations create compressions that reach the ear more frequently, resulting in a higher pitch.

Key Concept

Relationship between wave frequency and sound pitch

Estimated Time:45s

Question 147Question →

An atom is composed of a central core and surrounding subatomic particles. Match each atomic structure component on the left with its defining physical property and role on the right.

Click a left item, then click its matching right item

Show answer & explanation

Answer

Proton matches with the positively charged particle defining atomic number; Neutron matches with the neutral particle in the nucleus contributing to mass; Electron matches with the negatively charged particle orbiting outside the nucleus; Atomic nucleus matches with the dense central core containing nearly all atomic mass.

Each subatomic entity is matched according to its fundamental physical characteristics: protons are positively charged and determine atomic number; neutrons are uncharged nucleons that contribute to mass number; electrons are negative particles that orbit the nucleus; and the nucleus is the dense core where nearly all atomic mass is located.

Step-by-Step Solution

1

Identify the charge, location, and function of a proton

Protons are positively charged (

+1

) nucleons whose count equals the atomic number (

Z

).

Every unique chemical element is defined by its unique number of protons.

2

Identify the charge, location, and function of a neutron

Neutrons are neutral (

0

charge) nucleons that contribute to the atom's total mass number (

A

).

Neutrons provide nuclear stability and mass without affecting net nuclear charge.

3

Identify the charge, location, and function of an electron

Electrons are negatively charged (

-1

) particles located in electron shells surrounding the nucleus.

Electrons balance positive nuclear charge in neutral atoms and determine bonding behavior.

4

Identify the structural definition and mass distribution of the atomic nucleus

The atomic nucleus is the dense central region containing all protons and neutrons.

Because protons and neutrons are roughly

1836

times more massive than electrons, nearly all mass is located at the center.

Key Concept

Subatomic particle properties, charges, and atomic architecture

Estimated Time:45s

Question 148Question →

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 149Question →

A materials technician is evaluating the fundamental characteristics of several substances used in mechanical systems. Match each material property with its correct scientific definition.

Click a left item, then click its matching right item

Show answer & explanation

Answer

Ductility matches the ability of a solid to be drawn into wires under tensile stress; Viscosity matches the internal resistance of a fluid to flow; Flammability matches the chemical capacity of a substance to ignite and combust; Solubility matches the capacity of a solute to dissolve in a solvent.

Each property is accurately paired with its distinct physical or chemical behavior: ductility refers to tensile elongation into wire, viscosity measures fluid friction against flow, flammability measures chemical reactivity in combustion, and solubility determines dissolution capacity in a solvent.

Step-by-Step Solution

1

Identify mechanical physical properties of solids

Ductility represents tensile deformation into wires, distinguishing it from malleability (hammering into sheets).

Tensile stress applied to ductile metals allows elongation without brittle fracture.

2

Identify fluid transport physical properties

Viscosity represents fluid shear resistance and thickness.

Internal intermolecular friction governs how quickly or slowly fluids like motor oil or water flow.

3

Differentiate chemical properties from physical properties

Flammability involves chemical transformation through combustion.

Burning produces new chemical substances (carbon dioxide, water vapor, ash), making flammability a chemical property.

4

Identify mixture and dissolution characteristics

Solubility represents the maximum solute concentration in a solvent without altering chemical identities.

Dissolving is a physical process where solute particles disperse evenly within solvent molecules.

Key Concept

Classification and definitions of characteristic physical and chemical properties of matter

Estimated Time:1m 0s

Question 150Question →

A $400\text{ kg}$ patrol boat accelerates uniformly from rest to a speed of $18\text{ m/s}$ in $6\text{ seconds}$ across calm water. If a constant hydrodynamic resistance force of $300\text{ N}$ opposes the motion, what forward thrust force must the boat's engine produce?

1,200\text{ N}

1,500\text{ N}

900\text{ N}

4,200\text{ N}

Show answer & explanation

Answer: $1,500\text{ N}$

Answer

The boat's engine must produce a forward thrust of

1,500\text{ N}

.

To find the total thrust, first determine the acceleration from the velocity change (

18\text{ m/s} \div 6\text{ s} = 3\text{ m/s}^2

). Using Newton's Second Law (

F = ma

), the net forward force required is

400\text{ kg} \times 3\text{ m/s}^2 = 1,200\text{ N}

. Because

300\text{ N}

of water resistance opposes the boat, the engine must supply enough forward force to overcome drag plus provide the net accelerating force:

1,200\text{ N} + 300\text{ N} = 1,500\text{ N}

.

Step-by-Step Solution

1

Calculate the acceleration of the patrol boat using kinematic relations.

a = \frac{v_f - v_i}{t} = \frac{18\text{ m/s} - 0\text{ m/s}}{6\text{ s}} = 3\text{ m/s}^2

Uniform acceleration is defined as the change in velocity divided by the elapsed time.

2

Determine the net horizontal force required to accelerate the boat using Newton's Second Law.

F_{\text{net}} = m \cdot a = 400\text{ kg} \times 3\text{ m/s}^2 = 1,200\text{ N}

The net force acting on any mass is directly proportional to its acceleration (

F = ma

).

3

Apply the net force equation along the horizontal axis to solve for engine thrust.

F_{\text{thrust}} - F_{\text{resistance}} = F_{\text{net}} \implies F_{\text{thrust}} = 1,200\text{ N} + 300\text{ N} = 1,500\text{ N}

The engine thrust must overcome the backward resistive drag while providing the remaining force needed for forward acceleration.

Key Concept

Newton's Second Law and Net Force in One Dimension

Estimated Time:1m 0s

Question 151Question →

A neutral atom of sodium has an atomic number of $11$ and a mass number of $23$ . What is the total number of neutrons present in the nucleus of this atom?

11

12

23

34

Show answer & explanation

Answer: $12$

Answer

12

neutrons

The mass number (

23

) is the total count of protons and neutrons in the nucleus, and the atomic number (

11

) is the number of protons. Subtracting the atomic number from the mass number (

23 - 11 = 12

) yields the exact number of neutrons.

Step-by-Step Solution

1

Identify the number of protons and the total nucleon count from the given values.

Atomic number (

Z

) =

11

(protons), Mass number (

A

) =

23

(protons + neutrons)

The atomic number defines the number of protons, whereas the mass number represents the sum of protons and neutrons in the nucleus.

2

Calculate the number of neutrons by subtracting the atomic number from the mass number.

\text{Number of neutrons} = 23 - 11 = 12

Subtracting the proton count from the total mass number yields the quantity of neutrons.

Key Concept

The number of neutrons in an atom is calculated by subtracting the atomic number (number of protons) from the mass number (total protons and neutrons).

Estimated Time:35s

Question 152Question →

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 153Question →

A technician places a $500\text{ g}$ sample of liquid water into a sealed, airtight chamber and cools it until it freezes completely into solid ice. Which of the following statements correctly describes the changes in the sample's mass and volume?

The mass increases because solid ice is heavier than liquid water, while the volume remains constant.

The mass remains unchanged, but the volume decreases as the molecules pack closer together.

The mass remains unchanged, but the volume increases due to the expansion of water upon freezing.

The mass decreases because freezing triggers a chemical reaction that consumes matter, reducing the volume.

Show answer & explanation

Answer: The mass remains unchanged, but the volume increases due to the expansion of water upon freezing.

Answer

The mass remains unchanged, but the volume increases due to the expansion of water upon freezing.

Freezing is a physical phase change that does not alter the chemical identity or quantity of matter in a closed system, so mass is strictly conserved at

500\text{ g}

. Unlike most liquids that contract upon solidifying, water uniquely expands upon freezing due to hydrogen bonding forming a spacious hexagonal crystal lattice, causing its volume to increase.

Step-by-Step Solution

1

Evaluate the effect of freezing on the sample's mass in a sealed system.

The mass remains exactly

500\text{ g}

.

According to the Law of Conservation of Mass, the total quantity of matter in a closed system cannot change during a physical phase change.

2

Determine the effect of crystallization on the volume of water.

The volume of the water sample increases.

Water exhibits anomalous expansion upon freezing; hydrogen bonding locks water molecules into an open hexagonal lattice that takes up more space than the liquid phase.

3

Combine the mass and volume findings to identify the correct physical behavior.

Mass is conserved while volume increases (and density decreases).

Freezing is a physical process where mass stays constant while the physical arrangement of molecules increases the overall volume.

Key Concept

Conservation of mass during physical phase changes and the anomalous expansion of water upon freezing.

Estimated Time:1m 0s

Question 154Question →

In the study of classical mechanics, different physical quantities and forces describe how objects move and interact. Match each mechanical concept with its correct physical definition.

Click a left item, then click its matching right item

Show answer & explanation

Answer

Displacement matches with the straight-line vector from starting to final position; Average speed matches with total path distance divided by elapsed time; Normal force matches with the perpendicular support force exerted by a surface; Unbalanced force matches with a non-zero net force causing a change in velocity.

Each concept correctly aligns with its precise definition in classical kinematics and dynamics: displacement measures the net position vector, average speed measures scalar distance over time, the normal force provides perpendicular support, and an unbalanced force produces net acceleration.

Step-by-Step Solution

1

Identify the spatial vector measurement between two points.

Displacement represents the straight-line path and direction from initial to final position.

Unlike total distance, displacement depends only on the starting and ending positions.

2

Identify the scalar measure of motion rate.

Average speed equals total path distance divided by time elapsed.

Speed is scalar and does not take direction into account.

3

Identify the perpendicular contact force.

Normal force is the perpendicular push provided by a surface supporting a mass.

In physics, 'normal' means perpendicular to the contact plane.

4

Identify the cause of mechanical acceleration.

An unbalanced force produces a non-zero net force that accelerates an object.

Balanced forces maintain constant velocity (equilibrium), whereas unbalanced forces change motion.

Key Concept

Kinematic vector and scalar quantities alongside contact and net forces in mechanics

Estimated Time:1m 0s

Question 155Question →

An uncharged atom of chlorine has $17$ electrons and $18$ neutrons in its structure. What is the mass number of this chlorine atom?

Show answer & explanation

Answer: 35

Answer

The mass number of the chlorine atom is

35

.

For an uncharged atom, the number of protons equals the number of electrons (

17

). The mass number is the sum of protons and neutrons (

17 + 18 = 35

).

Step-by-Step Solution

1

Determine the number of protons in the atom

17

protons

In any electrically neutral atom, the number of positively charged protons is equal to the number of negatively charged electrons.

2

Add the number of protons and neutrons together

17 + 18 = 35

The mass number (

A

) of an atom is defined as the total number of protons plus neutrons located in its nucleus.

Key Concept

The mass number of an atom is the sum of its protons and neutrons. In a neutral atom, the number of protons equals the number of electrons.

Estimated Time:45s

Question 156Question →

When white light passes through a prism, it disperses into different colors of the visible spectrum. What is the correct order of the following colors of visible light when arranged from lowest wave frequency to highest wave frequency?

Drag items to arrange them in the correct order

Show answer & explanation

Answer

The correct sequence from lowest frequency to highest frequency is Red light, Yellow light, Green light, Violet light.

In the visible light spectrum, colors progress in order of decreasing wavelength and increasing frequency according to the sequence Red, Orange, Yellow, Green, Blue, Indigo, and Violet (ROYGBIV). Red light has the longest wavelength and lowest frequency, followed by yellow light, green light, and finally violet light, which has the shortest wavelength and highest frequency.

Step-by-Step Solution

1

Recall the order of the visible light spectrum from longest wavelength to shortest wavelength.

The standard sequence of visible light colors is Red, Orange, Yellow, Green, Blue, Indigo, and Violet (ROYGBIV).

Visible light wavelengths decrease progressively from red light (~700 nm) to violet light (~400 nm).

2

Determine the relationship between wavelength and frequency using the wave speed equation

c = \lambda f

.

Frequency is inversely proportional to wavelength (

f = \frac{c}{\lambda}

).

Because electromagnetic waves travel at the speed of light in a vacuum, longer wavelengths correspond to lower frequencies and shorter wavelengths correspond to higher frequencies.

3

Sequence the given colors in order of increasing frequency.

Red light (lowest frequency) -> Yellow light -> Green light -> Violet light (highest frequency).

Following the ROYGBIV sequence, wave frequency increases continuously from red to violet.

Key Concept

Relationship between wavelength, frequency, and color sequence in the visible light spectrum

Estimated Time:45s

Question 157Question →

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 158Question →

In a science laboratory, a technician analyzes a sample of phosphorus represented by the isotope symbol $^{31}_{15}\text{P}$ . What is the total number of neutrons contained in the nucleus of this phosphorus atom?

15

16

31

46

Show answer & explanation

Answer: $16$

Answer

16

neutrons

In standard isotopic notation

^{A}_{Z}\text{X}

, the superscript (

A = 31

) is the mass number, representing the combined number of protons and neutrons, while the subscript (

Z = 15

) is the atomic number, representing the number of protons. The number of neutrons is found by subtracting the atomic number from the mass number (

31 - 15 = 16

).

Step-by-Step Solution

1

Identify the mass number (

A

) and atomic number (

Z

) from the isotope notation

^{31}_{15}\text{P}

.

A = 31

and

Z = 15

.

In standard isotope notation, the upper superscript represents the mass number (

A

) and the lower subscript represents the atomic number (

Z

).

2

Calculate the number of neutrons using the relationship

\text{Neutrons} = A - Z

.

\text{Neutrons} = 31 - 15 = 16

.

The mass number equals the total number of protons and neutrons, while the atomic number equals the number of protons.

Key Concept

Calculating the number of neutrons in an atom using standard isotopic notation (

A - Z

).

Estimated Time:45s

Question 159Question →

When a person shouts inside a large empty gymnasium, they hear their voice repeated a moment later as an echo. Which wave behavior is directly responsible for producing an echo?

Diffraction

Reflection

Refraction

Absorption

Show answer & explanation

Answer: Reflection

Answer

Reflection is the wave behavior responsible for producing an echo.

An echo is heard when sound waves strike a rigid barrier and bounce back toward the listener. This bouncing back of a wave from a surface is defined as reflection.

Step-by-Step Solution

1

Analyze the physical scenario of an echo

Sound waves travel outward from the source, strike a hard obstacle such as a gymnasium wall, and bounce back to the listener.

Identifying the motion of the wave as returning after hitting a boundary isolates the specific physical mechanism.

2

Associate the wave behavior with standard physical terminology

The bouncing back of waves upon encountering an impenetrable surface is defined as reflection.

An echo is a direct real-world example of sound wave reflection.

Key Concept

Sound wave reflection and echo formation

Estimated Time:45s

Question 160Question →

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

Physical Science

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