An experimental automobile burns hydrogen for fuel. At the beginning of a test drive, the rigid 30.0-L tank was filled with hydrogen at 16.0 atm and 298 K. At the end of the drive, the temperature of the tank was still 298 K, but its pressure was 4.0 atm.

(a) How many moles of H₂ were burned during the drive?

(b) How much heat, in kilojoules, was given off by the combustion of that amount of hydrogen?