Chapter 17.2, Problem 21LC

Interpretation Introduction

Interpretation: The amount of heat released when $\text{12}\text{.5g}$ of ethanol burns.

Concept introduction:

Thermochemical equations are balanced stoichiometric chemical equations that are accompanied by information about heat change.

Exothermic reactions are those in which heat is absorbed by the reactants and enthalpy change for the reaction is positive.

Answer to Problem 21LC

The amount of heat released when $\text{12}\text{.5g}$ of ethanol burns is $\text{370}\text{.7 kJ}$

Explanation of Solution

The given chemical equation is:

  ${\text{C}}_2{\text{H}}_6{\text{O(l)+3O}}_2\text{(g)}\to 2{\text{CO}}_{\text{2}}{\text{(g)+3H}}_2\text{O(l) }\Delta \text{H= -1368kJ}$

Thus it is given that when 1 mol of ethanol burns, the energy released is $\text{1368 kJ}$

Given the amount of ethanol = $\text{12}\text{.5 g}$

Moles of ethanol are found by dividing the given amount of ethanol by the molecular mass of ethanol.

Moles of ethanol given = $\frac{12.5\text{g}}{46.07gmo{l}^{-1}}=0.271mol$

For the burning of $\text{1 mol}$ of ethanol, heat released is = $\text{1368 kJ}$

Thus, for the burning of $\text{0}\text{.271 mol}$ , heat released is = $\frac{\text{1368kJ}}{1\text{mol}}\times 0.271\text{mol=370}\text{.7kJ}$