To calculate the new pressure, we need to relate pressure with the temperature and the volume of the system. For simplification, we assume that it is an ideal gas so we use the equation PV = nRT where nR is a constant term. We calculate as follows:
P1V1/T1 = P2V2/T2
800(5.0) / 223.15 = P2 (7.0)/310.15
P2 = 794.21 mmHg