Question

Calculate the standard enthalpy change for the complete combustion of methane gas (CH4(g)) at constant pressure, given the balanced equation: CH4(g) + 2O2(g) → CO2(g) + 2H2O(l). The standard enthalpies of formation of CO2(g), H2O(l), and CH4(g) are -393.5 kJ/mol, -285.8 kJ/mol, and -74.8 kJ/mol, respectively.

Answer 1

To calculate the standard enthalpy change for the complete combustion of methane gas, we can use the following formula:H =  Hf products  -  Hf reactants where H is the standard enthalpy change, and Hf is the standard enthalpy of formation.For the given balanced equation:CH4 g  + 2O2 g   CO2 g  + 2H2O l The standard enthalpies of formation are:Hf CH4 g   = -74.8 kJ/molHf O2 g   = 0 kJ/mol  since O2 is in its standard state Hf CO2 g   = -393.5 kJ/molHf H2O l   = -285.8 kJ/molNow, we can plug these values into the formula:H = [1   -393.5 kJ/mol  + 2   -285.8 kJ/mol ] - [1   -74.8 kJ/mol  + 2  0 kJ/mol]H =  -393.5 - 2  285.8 + 74.8  kJ/molH =  -393.5 - 571.6 + 74.8  kJ/molH =  -964.3 + 74.8  kJ/molH = -889.5 kJ/molThe standard enthalpy change for the complete combustion of methane gas at constant pressure is -889.5 kJ/mol.