Chapter 6, Problem 6.65P

(a)

Interpretation Introduction

Interpretation:

The balanced thermochemical equation for the combustion of ethylene $\left({\text{C}}_{\text{2}}{\text{H}}_4\right)$ when the heat of the reaction is $-1411\text{kJ/mol}$ is to be determined.

Concept introduction:

The balanced thermochemical equation is the type of chemical equation that also mentions the heat of the reaction. The general balanced thermochemical equation is as follows:

$\text{A}+\text{B}\to \text{C}$                                       $\Delta H_{\text{rxn}}=x$

Here, $x$ is the enthalpy of the reaction.

Endothermic reactions are the reactions in which energy in the form of the heat or light is absorbed by the reactant for the formation of the product. $H_{\text{Product}}$ is greater than $H_{\text{Reactant}}$ in the endothermic reactions.

Exothermic reactions are the reactions in which energy in the form of the heat or light is released with the product. $H_{\text{Reactant}}$ is greater than $H_{\text{Product}}$ in the exothermic reactions.

(b)

Interpretation Introduction

Interpretation:

The mass of ${\text{C}}_{\text{2}}{\text{H}}_4$ that is burnt to release $70\text{kJ}$ is to be determined.

Concept introduction:

The internal energy of a process is the summation of the kinetic energy and potential energy associated with the process. In chemical reactions, the change in internal energy $\left(\Delta E\right)$ is the difference in the energy of the product and reactant but at constant pressure, the $P\Delta V$ work gets eliminated and the change in enthalpy $\left(\Delta H\right)$ is measured.

In chemical reactions, the change in enthalpy $\left(\Delta H\right)$ is the difference in the energy of the product and reactant. The general expression to calculate $\Delta H$ is,

$\Delta H=H_{\text{Product}}-H_{\text{Reactant}}$ (1)

Here,

$\Delta H$ is the change in enthalpy of the system.

$H_{\text{Product}}$ is the enthalpy of the products.

$H_{\text{Reactant}}$ is the enthalpy of the reactants.

Endothermic reactions are the reactions in which energy in the form of the heat or light is absorbed by the reactant for the formation of the product. $H_{\text{Product}}$ is greater than $H_{\text{Reactant}}$ in the endothermic reactions.

Exothermic reactions are the reactions in which energy in the form of the heat or light is released with the product. $H_{\text{Reactant}}$ is greater than $H_{\text{Product}}$ in the exothermic reactions.