Chapter 17, Problem 59A

Interpretation Introduction

Interpretation: The amount of heat released during the chemical reaction is to be found.

Concept introduction: The reactant in a chemical process known as the limiting reactant controls how much product can be produced. When the limiting reactant is fully consumed, the reaction will come to an end. The reactant in a chemical reaction known as the excess reactant is what is left over after the limiting reactant has been entirely consumed.

Answer to Problem 59A

The kilojoules of heat released when $\text{0}\text{.75 mol}$ of $\text{Mg}$ burns in excess of oxygen is $451.5\text{ kJ}$

Explanation of Solution

The given chemical reaction is

  ${\text{2Mg(s)+O}}_{\text{2}}\text{(g)}\to \text{2MgO(s)+1204 kJ}$

The heat has been released which means the reaction is exothermic. Also, it is given that oxygen is in excess, thus $\text{Mg}$ is the limiting reactant and will decide the amount of formed and heat released.

It is given that when $\text{2 mol}$ of $\text{Mg}$ is burnt, the energy released is $\text{1204 kJ}$

Thus, when $\text{0}\text{.75 mol}$ of $\text{Mg}$ is burnt, energy released is = $\frac{1204\text{ kJ}}{\text{2 mol}}\times 0.75\text{ mol}=451.5\text{ kJ}$