To calculate the amount of heat energy released, we first need to determine the number of moles of methane CH4 in 25 grams.The molar mass of methane CH4 is:C: 12.01 g/molH: 1.01 g/molTotal: 12.01 + 4 x 1.01 = 16.05 g/molNow, we can find the number of moles of methane in 25 grams:moles = mass / molar massmoles = 25 g / 16.05 g/mol = 1.557 molesSince the enthalpy of combustion for methane is -890.4 kJ/mol, we can now calculate the amount of heat energy released:heat energy = moles enthalpy of combustionheat energy = 1.557 moles -890.4 kJ/mol = -1385.6 kJTherefore, the amount of heat energy released when 25 grams of methane is burned completely in oxygen gas is approximately -1385.6 kJ. The negative sign indicates that the reaction is exothermic and releases heat.