The balanced combustion of methane is shown below.
CH4(g) + O2(g) CO2(g) + H2O(g) ΔH = –890 kJ mol–1
Determine how much energy is released when 60 L of methane at 25 MPa and 25°C undergoes complete combustion.
First, we need to calculate the number of moles of methane present in 60 L at 25 MPa and 25°C. We can use the ideal gas law:
PV = nRT
n = (PV)/(RT)
n = ((25 MPa) x (0.06 m3))/(8.314 J/mol∙K x 298 K)
n = 0.00968 mol
According to the balanced equation, 1 mole of methane releases 890 kJ of energy. Therefore, 0.00968 mol of methane will release:
0.00968 mol x (-890 kJ/mol) = -8.61 kJ
The negative sign indicates that energy is released (exothermic reaction).
Therefore, the combustion of 60 L of methane at 25 MPa and 25°C will release 8.61 kJ of energy.
To determine the amount of energy released when 60 L of methane undergoes complete combustion, we need to calculate the number of moles of methane, and then multiply it by the enthalpy change of combustion.
1. Convert the given conditions from liters and MPa to moles and atmospheres:
Using the ideal gas law equation: PV = nRT
- Convert 60 L to moles:
V = nRT/P
n = PV/RT
= (25 MPa * 60 L) / [0.0821 L.atm/mol.K * (25 + 273.15) K]
= 29.56 moles
2. Multiply the number of moles by the enthalpy change value:
Energy released = n * ΔH
= 29.56 moles * (-890 kJ/mol)
= -26,259.4 kJ
Therefore, approximately 26,259.4 kJ of energy is released when 60 L of methane at 25 MPa and 25°C undergoes complete combustion.