Question

104 J of work is done on a certain volume of a gas. If the gas releases 125 kJ of heat, calculate the change in internal energy of the gas.

Answer 1

We know from the first law of thermodynamics that

ΔU = Q − W    ...(i)

We have given that, W = 104 J, This work is done on the gas, hence we write W = −104 J.

Similarly, the heat is released by the gas and we write Q = −125 kJ = −125000 J.

Therefore, from the first law of thermodynamics, we have,

ΔU = |Q| − |W|

∴ ΔU = (12500 − 104)

= 124896 J

= 124.896 kJ

= 124.9 kJ