Chapter U4.2, Problem 3E

(a)

Interpretation Introduction

Interpretation: The given chemical equation needs to be explained.

  ${\text{2Mg}}_{\text{(s)}}{\text{ + 2HCl}}_{\text{ (aq)}}\stackrel{}{\to }{\text{H}}_{\text{2(g)}}{\text{ + MgCl}}_{\text{2(aq)}}$

Concept Introduction: A physical change is associated with change in the physical state of the substance whereas the chemical composition remains same.

A chemical change is associated with the change in the chemical composition of the substance. Chemical equation is the symbolic representation of a chemical change in which the chemical formula of the substances are written with their physical states.

Explanation of Solution

The reaction is as follows:

  ${\text{2Mg}}_{\text{(s)}}{\text{ + 2HCl}}_{\text{ (aq)}}\stackrel{}{\to }{\text{H}}_{\text{2(g)}}{\text{ + MgCl}}_{\text{2(aq)}}$

In the given reaction, solid magnesium reacts with aqueous solution of HCl. Thus, both solid magnesium and aqueous solution of HCl are reactant here. The reaction leads to the formation of hydrogen gas and aqueous solution of magnesium chloride as product of reaction.

Thus it is a displacement reaction which forms hydrogen gas aqueous solution of magnesium chloride.

(b)

Interpretation Introduction

Interpretation: The given chemical equation needs to be described.

  ${\text{2 H}}_{\text{2}}{\text{O}}_{\text{2}}{}_{\text{ (aq)}}\stackrel{}{\to }{\text{2H}}_{\text{2}}{\text{O}}_{\text{(l)}}{\text{ + O}}_{\text{2(g)}}$

Concept Introduction: A physical change is associated with change in the physical state of the substance whereas the chemical composition remains same.

A chemical change is associated with the change in the chemical composition of the substance. Chemical equation is the symbolic representation of a chemical change in which the chemical formula of the substances are written with their physical states.

Answer to Problem 3E

It represents the dissociation reaction of hydrogen peroxide which leads to the formation of water and oxygen gas.

Explanation of Solution

The reaction is as follows:

  ${\text{2 H}}_{\text{2}}{\text{O}}_{\text{2}}{}_{\text{ (aq)}}\stackrel{}{\to }{\text{2H}}_{\text{2}}{\text{O}}_{\text{(l)}}{\text{ + O}}_{\text{2(g)}}$

In the given reaction, aqueous solution of hydrogen peroxide dissociates to water and oxygen gas. Thus it is an example of dissociation reaction.

Here, hydrogen peroxide is reactant molecule whereas water and oxygen gas are product of the reaction.

(c)

Interpretation Introduction

Interpretation: The given chemical equation needs to be described.

  ${\text{2 NaCl}}_{\text{ (aq)}}{\text{+Pb(NO}}_{\text{3}}{\text{)}}_{\text{2(aq)}}\stackrel{}{\to }{\text{2NaNO}}_{\text{3}}{}_{\text{(aq)}}{\text{ + PbCl}}_{\text{2(s)}}$

Concept Introduction: A physical change is associated with change in the physical state of the substance whereas the chemical composition remains same.

A chemical change is associated with the change in the chemical composition of the substance. Chemical equation is the symbolic representation of a chemical change in which the chemical formula of the substances are written with their physical states.

Answer to Problem 3E

It represents a double displacement reaction in which sodium chloride and lead nitrate react to form lead chloride and sodium nitrate as final products.

Explanation of Solution

The given reaction is as follows:

  ${\text{2 NaCl}}_{\text{ (aq)}}{\text{+Pb(NO}}_{\text{3}}{\text{)}}_{\text{2(aq)}}\stackrel{}{\to }{\text{2NaNO}}_{\text{3}}{}_{\text{(aq)}}{\text{ + PbCl}}_{\text{2(s)}}$

In the given reaction, sodium chloride reacts with lead nitrate in aqueous solution. It forms sodium nitrate and lead chloride. Here, lead chloride precipitates and sodium nitrate remains in the solution as it is soluble in water.

Thus, sodium chloride and lead nitrate are reactant molecules whereas sodium nitrate and lead chloride are formed as product.

It is an example of double displacement reaction and also called as precipitation reaction as precipitate is formed during the reaction.