Chapter 6, Problem 6.87P

(a)

Interpretation Introduction

Interpretation:

A balanced equation for the combustion of stearic acid is to be written.

Concept introduction:

The standard enthalpy of formation $\left(\Delta H_{\text{f}}^{°}\right)$ is the enthalpy change of the formation of $1\text{mol}$ of compound from its elements and the reactants and products, in this case, is also present in their standard state.

Standard state includes $1\text{atm}$ pressure for gases, $1M$ concentration for substances in the aqueous phase and the most stable form of substance at $1\text{atm}$ pressure and $298\text{K}$ temperature. For example, metal like sodium exists in solid state and molecular elements like halogen exist in a gaseous state.

(b)

Interpretation Introduction

Interpretation:

$\Delta H_{\text{rxn}}^{°}$ for the combustion of stearic acid is to be determined.

Concept introduction:

The standard enthalpy of reaction is calculated by the summation of standard enthalpy of formation of the product minus the summation of standard enthalpy of formation of product at the standard conditions. The formula to calculate the standard enthalpy of reaction $\left(\Delta H_{\text{rxn}}^{°}\right)$ is as follows:

$\Delta H_{\text{rxn}}^{°}=\sum m\Delta H_{\text{f (products)}}^{°}-\sum m\Delta H_{\text{f (reactants)}}^{°}$

Here, m and n are the stoichiometric coefficients of reactants and product in the balanced chemical equation.

(c)

Interpretation Introduction

Interpretation:

The heat that is released in $\text{kJ}$ and $\text{kcal}$ when $1.00\text{ g}$ of stearic acid is burned completely is to be calculated.

Concept introduction:

Heat $\left(q\right)$ is the energy transferred as a consequence of the difference of the temperature between the system and surrounding.

The heat released by the system is negative and the heat taken by the system is positive.

The amount of heat released by the system is equal to the amount of amount absorbed by the surrounding.

The expression to convert $\text{kcal}$ into $\text{kJ}$ is:

$\text{1}\text{kcal}=4.184\text{kJ}$

(d)

Interpretation Introduction

Interpretation:

Whether the data that a candy containing $11.0\text{ g}$ fat and provides $100\text{ Cal}$ energy is consistent with the answer calculated in part (c) is to be determined.

Concept introduction:

Heat $\left(q\right)$ is the energy transferred as a consequence of the difference of the temperature between the system and surrounding.

The heat released by the system is negative and the heat taken by the system is positive.

The amount of heat released by the system is equal to the amount of amount absorbed by the surrounding.

The conversion factor to convert nutritional calorie $\left(\text{Calorie}\right)$ into $\text{kcal}$ is:

$\text{1}\text{Calorie}=1\text{kcal}$