Question

If the work done on the system or by the system is zero, then which one of the following statemen for a gas kept at a certain temperature is called?

(a) Change in internal energy of the system is equal to flow of the heat in or out of the system.

(b) Change in internal energy of the system is less than heat transferred.

(c) Change in internal energy of the system is more than the heat flow.

(d) Cannot be determined

Answer 1

(a) Change in internal energy of the system is equal to flow of the heat in or out of the system.

For first law of thermodynamics, 

ΔQ = ΔU + ΔW

where, ΔQ = heat, ΔU = change in internal energy and AW work done.

Since, ΔW = 0, so ΔQ = ΔU.

Hence, there is change in internal energy of the system is equal to flow of heat in or out of the system.