JEE Main 2025 Apr 3 Shift 2, Chemistry Q23: Calorimetry

JEE Main2025Apr 3, Shift 2Chemistry

A sample of n-octane (1.14 g) was completely burnt in excess of oxygen in a bomb calorimeter, whose heat capacity is 5 kJ K $^{- 1}$ . As a result of combustion reaction, the temperature of the calorimeter is increased by 5 K. The magnitude of the heat of combustion of octane at constant volume is _____ kJ mol $^{- 1}$ (nearest integer).

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Solution

Moles of n-octane burnt (M = 114 g mol $^{- 1}$ ): $n = \frac{1.14}{114} = 0.01$ mol.

Heat absorbed by the calorimeter: $q = C Δ T = 5 \times 5 = 25$ kJ. Since the bomb is sealed (constant volume), this equals $- Δ U$ for the combustion.

Heat of combustion per mole: $\frac{25}{0.01} = 2500$ kJ mol $^{- 1}$ .

$∴$ The magnitude is 2500 kJ mol $^{- 1}$ .

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JEE Main 2025 Apr 3 Shift 2, Chemistry Q23: Calorimetry

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