Question

Calcium carbide (CaC2) reacts with water to form acetylene (C2H2) gas and calcium hydroxide (Ca(OH)2). If the ΔH for:

CaC2(s) + 2H2O(l) = Ca(OH)2(s) + C2H2(g)

is -127 kJ, then what is the enthalpy of formation for calcium carbide? The ΔH of formation for H2O(l), Ca(OH)2(s) and C2H2(g) are -286, -986, 227 kJ/mol respectively. The units are kJ.

Answer 1

dHrxn = (n*dHf products) - (n*dHf products)
dHrxn = -127 = (n*dHf .....etc)
Substitute and solve for dHf CaC2 which is the only unknown in the equation.