Question

When an ideal diatomic gas is heated at constant pressure then what fraction of heat given is used to increase internal energy of gas?

Answer 1

If it is heated at constant pressure, the volume must increase
heat in = change in internal energy + work out
dQ = dU + dW
P V = n R T
constant pressure
P dV = n R dT = work out
Change in internal energy = n Cv dT = n(5/2)R dT for diatomic gas
total heat required = n R dT + (5/2)n R dT

so our answer is (5/2) / (1+5/2)
= 5/(2+5) = 5/7