Question

An insulator container contains 4 moles of an ideal diatomic gas at temperature T. Heat Q is supplied to this gas, due to which 2 moles of the gas

are dissociated into atoms but temperature of the gas remains constant. Then

• A.
• B.
• C.
• D.

Answer 1

The correct option is B

$Q=△U=U_f-U_i$ = [internal energy of 4 moles of a monoatomic gas + internal

energy of 2 moles of a diatomic gas] - [internal energy of 4 moles of a diatomic gas]

$=(4\times \frac{3}{2}RT+2\times \frac{5}{2}RT)-(4\times \frac{5}{2}RT)=RT$

Note : (a) 2 moles of diatomic gas becomes 4 moles of a monoatomic gas when gas dissociated into atoms.

(b) Internal energy of m moles of an ideal gas of degrees of freedom F is given by $U=\frac{f}{2}\mu RT$

F = 3 for a monoatomic gas and 5 for diatomic gas.