(1) Choose the state of A as the initial state and the state of B as the final state, which is determined by Charlie's law:

PATA=PBTB

Solution: pa = PBT ATB = 8.0× 104 pa.

(2) The volume of gas from state A to state B is constant, and the external work is 0. According to the first law of thermodynamics, the increment of internal energy of gas is:

△E=W+Q=6.0× 102J

A: The pressure of gas in state A is 8.0×104; The increment of internal energy of gas is 6.0× 102.