1. The problem statement, all variables and given/known data We give 70J as heat to a diatomic gas, which then expands at constant pressure. The gas molecules rotate but do not oscillate. By how much does the internal energy of the gas increase. 2. Relevant equations 3. The attempt at a solution I did it this way: Heat added = nCp dT = 70J. Let Internal energy = nCv dT = x (say). Dividing both equations, we obtain: Cp/Cv = 70/x. But, Cp/Cv is nothing but the ration of speicifc heat which for a diatomic gas is known to be 7/5. So, x = 50J. Am I correct? the solution is not given in the book! Thanks a ton in advance!