Chapter 7, Problem 7.76CP

(a)

Interpretation Introduction

Interpretation:

The amount of heat released when $0.255mol$ of aluminum has reacted in $kJ$ is to be determined.

Concept Introduction:

Enthalpy $\text{H}$: it is the total amount of heat in a particular system.

The value of heat formed in a reaction $\text{ΔH}$ is calculated by the formula,

$\text{ΔH=}{{\displaystyle \sum \left(BondDissociationEnergy\right)}}_{\left(\text{reactants}\right)}-{{\displaystyle \sum \left(BondDissociationEnergy\right)}}_{\left(\text{products}\right)}$

If the value obtained for $\text{ΔH}$ in a reaction is positive then it is an endothermic reaction whereas the value obtained for $\text{ΔH}$ is negative it is an exothermic reaction.

Conversion of $kcal$ to joules is $1kcal=4184J$

(b)

Interpretation Introduction

Interpretation:

The amount of heat released when $5g$ of aluminum has reacted in $kcal$ is to be determined.

Concept Introduction:

Enthalpy $\text{H}$: it is the total amount of heat in a particular system.

The value of heat formed in a reaction $\text{ΔH}$ is calculated by the formula,

$\text{ΔH=}{{\displaystyle \sum \left(BondDissociationEnergy\right)}}_{\left(\text{reactants}\right)}-{{\displaystyle \sum \left(BondDissociationEnergy\right)}}_{\left(\text{products}\right)}$

If the value obtained for $\text{ΔH}$ in a reaction is positive then it is an endothermic reaction whereas the value obtained for $\text{ΔH}$ is negative it is an exothermic reaction.

Conversion of $kcal$ to joules is $1kcal=4184J$

From its given mass is,

$\text{Number of moles}\text{=}\frac{\text{Given}\text{mass}}{\text{Molecular}\text{mass}}$