Question

High-purity benzoic acid is used as a standard for calibrating bomb calorimeters. A 1.221g sample burns in a colorimeter (heat capacity=1365) that contains exactly 1.37kg of water. What temperature change is observed?

Answer 1

To calculate the temperature change in a bomb calorimeter after burning benzoic acid, multiply the mass of the acid by the enthalpy of combustion to find the heat released, and divide this by the heat capacity of the calorimeter to find the change in temperature. The calculation shows a temperature increase of approximately 23.59°C.

Step-by-step explanation:

The question involves calculating the temperature change observed in a bomb calorimeter with a specific heat capacity, after burning a known mass of benzoic acid to calibrate the device. The enthalpy of combustion (ΔH comb) of benzoic acid is given as -26.38 kJ/g. To calculate the temperature change (ΔT), we first determine the total heat released (q) by multiplying the mass of benzoic acid by its ΔH comb. Then, using the formula ΔT = q / Ccalorimeter, where Ccalorimeter is the heat capacity of the calorimeter, we can find the ΔT

First, calculate the total heat released during combustion:

q = mass of benzoic acid × ΔH comb = 1.221g × (-26.38 kJ/g) = -32.21978 kJ.

Next, calculate the temperature change:

ΔT = q / Ccalorimeter = -32.21978 kJ / 1365 J/°C = -32.21978 kJ * 1000 J/kJ / 1365 J/°C = -23.59°C (negative sign indicates an exothermic reaction resulting in a rise in temperature).

Therefore, the observed temperature change when burning the benzoic acid sample in the calorimeter is approximately 23.59°C.