Question

A slice of banana weighing 2.502 g was burnt in a bomb calorimeter producing a temperature rise of ${3.05}^{\circ }C$. The combustion of 0.316 g of benzoic acid in the same calorimeter produced a temperature rise of ${3.24}^{\circ }C$. The heat of combustion of benzoic acid at constant volume is $-3227kJmo{l}^{-1}$. If the average banana mass is 125 g, the kilojoules of energy can be obtained from 1 average banana is: (nearest integer value)

Answer 1

$q=mS.\Delta T$ for combustion of benzoic acid
($Note:$ In bomb calorimeter reaction is made at constant volume)

The molar mass of benzoic acid= 122g

122 g of benzoic acid produces -3227 $KJmo{l}^{-1}$ heat of combustion

$q=\frac{0.316\times 3227}{122}=m\times S\times 3.24$

$\therefore$ Water equivalent of bomb calorimeter $\left(mS\right)$

$m\times S=\frac{0.316\times 3227}{122\times 3.24}=2.58kJ{/}^{\circ }C$

For banana slice; $q=mS\times \Delta T$

$q=2.58\times 3.05$

$=7.87kJper2.502gbanana$

$\therefore Heatproducedby125gbanana=\frac{7.87\times 125}{2.502}=393.18kJ\approx 393kJ$

Hence, the heat produced by 125g of banana will be 393 $kJ$