When solid zinc metal is immersed in hydrochloric acid, a single displacement reaction occ… — Armed Services Vocational Aptitude Battery (ASVAB)

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?

Answer:

\text{Zn} + 【2】\text{HCl} \rightarrow \text{ZnCl}_2 + 【H2】

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

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.

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.

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

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