Acetylene, C2H2, is a gas commonly used in welding. It is formed in the reaction of calcium carbide, CaC2, with water. Given the thermochemical equations, calculate the value of ?H°f for acetylene in units of kilojoules per mole.
CaO(s) + H2O(l) ? Ca(OH)2(s) ?H°=-65.3 kJ
2CaO(s) + 5C(s) ? 2CaC2(s) + CO2(g) ?H°=+753 kJ
CaCO3(s) ? CaO(s) + CO2(g) ?H° = +178 kJ
CaC2(s) + 2H2O(l) ? Ca(OH)2(s) + C2H2(g) ?H°=-126 kJ
C(s) + O2(g) ? CO2(g) ?H°=-393.5 kJ
2H2O(l) ? 2H2(g) + O2(g) ?H°=+572 kJ