One kilogram of water vapor (as an ideal gas) is filled in a frictionless piston-cylinder assembly. The piston can move freely in the cylinder and it is in surroundings of 1 atm. Initially, the water vapor is at 400 K and 1 atm. Heat transfer to the water vapor occurs until the final temperature is 800 K. Determine the heat transfer for the process. (Do not assume constant cv and cp).