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  • In a constant volume calorimeter, of a gas with molar mass <img alt="28 \:\:g \:mol^{-1}" src="htt

In a constant volume calorimeter,2.5 \:g of a gas with molar mass 28 \:\:g \:mol^{-1} was burnt in excess oxygen at 300 \:k. The temperature of the calorimeter was found to increase from 300\: K\: to\:\: 300.45 \:\:K due to combustion process.Given that the Heat capacity of the calorimeter is 205 \:\: kJ \:K^{-1}, the numerical value for the enthalpy of combustion of the gas in kJ\:\: mol^{-1} is:

Option: 1

9\:\:kJ\:\:mol^{-1}

 


Option: 2

11.6\:\:kJ\:\:mol^{-1}


Option: 3

13.6\:\:kJ\:\:mol^{-1}


Option: 4

12.6\:\:kJ\:\:mol^{-1}


Answers (1)

best_answer

As we have learned,

Bomb Calorimeter -

In the laboratory, it is measured by using polythene on polystyrene bottles as follows.

Here 10 ml pf each of acid and alkali having the same normality are taken in separate bottles and temperature is noted at regular intervals. When the constant temperature is achieved, the alkali solution is added to the acid solution. The mixture is stirred and the highest temperature is noted.

Suppose T1 and T2  are initial and final temperatures here then

The rise in temperature = (T1-T2) K

Here specific heat capacity of the solution is assumed to be the same as that of water while heat capacity can be ignored as it is quite less than that of solution.

\mathrm{Q=m s\left(T_2-T_1\right) =ms\Delta T}

Given , \Delta T=300.45-300=45\:K

The total energy released during combustion of 2.5 g gas

\mathrm{=(ms)\times\Delta T}                                                                                                            =2.5\times4.5

So , heat released by 1 mole of gas combustion 

    \begin{aligned} & =28 / 2.5 \times 1.125 \\ & =12.6 \mathrm{~kJ} \mathrm{~mol}^{-1} \end{aligned}

Posted by

Rishi

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