Question

High-purity benzoic acid (C₆H₅COOH; ΔH_rxn for combustion = −3227 kJ/mol) is used as a standard for calibrating bomb calorimeters. A 1.221-g sample burns in a calorimeter (heat capacity = 1365 J/°C) that contains exactly 1.370 kg of water. What temperature change is observed?

Answer 1

Sample of benzoic acid =1.221 g,and C₆H₅COOH; ΔH_rxn for combustion = −3227 kJ/mol) and calorimeter heat capacity = 1365 J/°C which has exactly 1.37 Kg of water

Firstly we calculate mole of benzoic acid

number of moles, $n= \frac{given mass}{molar mass}= \frac{1.221}{122.1}=0.01$

Now enthalpy of combustion=$(0.01 \times 3227)=32.27 KJ$

As per principle of calorimetry

Heat released by combustion= heat absorb by calorimeter+ heat absorb by water

$32270 = q_1 \Delta T + q_2 \Delta T$ (q₂= mc) here c = specific heat of water= 4.2 J

$32270 = 1365 \Delta T + 1370 \times 4.2 \Delta T$

$32270 = 7119 \Delta T$

$\Delta T=4.533 K$ This is change in temperature