Question

Gas contained in a closed system consisting of piston cylinder arrangement is expanded. Work done by the gas during expansion is 50 kj. Decrease in internal energy of the gas during expansion is 30 kj. Heat transfer during the process is equal to:

Answer 1

Answer:-  q = 20 kj.

Solution:- From first law of thermodynamics:

$\Delta E=q+w$

where, $\Delta E$ is the change to internal energy, q is the heat added to the system or lost by the system and w is the work done by the system or on the system.

Since the expansion of the gas is taking place, the work is done by the system and so w is negative, w = -50 kj.

There is decrease in internal energy means $\Delta E$  = -30 kj

It's asking to calculate q. Let's plug in the values in the above formula:

-30 kj = q -50 kj

q = -30 kj + 50 kj

q = 20 kj

So, 20 kj of heat is added to the system during the process of expansion of the gas.