When expanding, the gas performed work equal to 25 J. find the change in its internal energy

When expanding, the gas performed work equal to 25 J. find the change in its internal energy if the amount of heat supplied to the gas is 42 J.

A = 25 J.

Q = 42 J.

ΔU -?

According to the first law of thermodynamics, the amount of thermal energy Q, which is imparted to the gas, goes to change its internal energy ΔU and to perform mechanical work A by it: Q = ΔU + A.

ΔU = Q – A.

In other words, the internal energy of the gas U can be changed in two ways: by performing mechanical work A by the gas, transferring the amount of heat Q to it.

ΔU = 42 J – 25 J = 17 J.

Since ΔU> 0, then the gas is heated.

Answer: the internal energy of the gas increased by ΔU = 17 J.