Using the given standard enthalpies of formation and the heat of reaction, calculate the standard heat of formation of C2H2(g).

Question

Using the given standard enthalpies of formation and the heat of reaction, calculate the standard heat of formation of C2H2(g).

 

CaC₂(s) + 2 H₂O(l) → Ca(OH)₂(s) + C₂H₂(g)   ΔH_rxn = -127.2 kJ/mol

 

ΔH_f° of Ca(OH)₂(s) = -986.2 kJ/mol

ΔH_f° of CaC₂(s) = -60.6 kJ/mol

ΔH_f° of H₂O(l) = -285.85 kJ/mol

Answer 1

∆Hrxn = ∑∆Hf products - ∑∆Hf reactants

∆Hf reactants = -60.6 + 2*-285.85 = -60.6 + (-571.7) = -632.3

∆Hf products = -986.2 + x where x = ∆Hf C₂H₂(g)

∆Hrxn = ∑∆Hf products - ∑∆Hf reactants

-127.2 = (-986.2 + x) - (-632.3)

-127.2 = (-986.2 + x) + 632.3

x = -226.7 kJ/mol = ∆Hf for C₂H₂