0 . 3 g of ethane undergoes combustion at 27 ° C in a bomb calorimeter. The temperature of calorimeter system (including the water) is found to rise by 0 . 5 ° C . The heat evolved during combustion o

Question

0 . 3 g of ethane undergoes combustion at 27 ° C in a bomb calorimeter. The temperature of calorimeter system (including the water) is found to rise by 0 . 5 ° C . The heat evolved during combustion of ethane at constant pressure is kJmol - 1 . (Nearest integer) [Given : The heat capacity of the calorimeter system is 20 kJ K - 1 , R = 8 . 3 JK - 1 mol - 1 . Assume ideal gas behaviour. Assume ideal gas behaviour. Atomic mass of C and H are 12 and 1 g mol - 1 respectively]

TestHub · Accepted Answer

The bomb calorimeter is an instrument used to measure the heat of reaction at a fixed volume and the measured heat which is called the change of internal energy.
By combustion of $1$ mole

$C_{2} H_{6} (ΔU) = - \frac{Heat capacity \times ∆ T}{mass} \times Molar mass = - \frac{20 \times 0.5}{0.3} \times 30 = - 1000 kJ$

$C_{2} H_{6} (g) + 7 / 2 O_{2} (g) \to 2 {CO}_{2} (g) + 3 H_{2} O (l)$

$Δ ng = 2 - (2 + 7 / 2) = - (7 / 2)$

$ΔH = ΔU + ΔnRT$

$= - 1000 - 7 / 2 \times 8.3 \times 300 kJ$

$= - 1000 - 6.225$

$= - 1006 kJ$

So heat released $= 1006 kJ {mol}^{- 1}$

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