Calculate the final temperature inside the vessel

Question

A spark causes the CH₄ to completely combust, an empty 4.00 liter steel vessel is filled with 1.0 atm CH_4(g) and 4.0 atm O_{2 (g)} at 300 C, according to the following equation:
CH_{4 (g)} + 2O_{2 (g)} ---> CO_{2 (g)}+ 2H₂O_(g)         Delta H = -802 kJ/mol
1.Calculate the final temperature inside the vessel after combustion; neglect any loss of heat to the vessel or surroundings. Where the mixture of gases has an average molar heat capacity of 21J/mol * C
2. Determine the partial pressure of CO_{2 (g)} in the vessel after combustion.