Consider the reaction.
2 upper C (s, graphite) plus upper H subscript 2 right arrow upper C subscript 2 upper H subscript 2 (g).
Standard Enthalpies of Formation
Substance
DHf (kJ/mol)
C2 H2 (g)
226.73
CaCO3 (s)
–1206.92
CaO (s)
–635.09
CO (g)
–110.525
CO2 (g)
–393.509
H 2 O (I)
–285.8
H 2 O (g)
–241.818
C (s), diamond
1.895
C (s), graphite
0.0
Based on the equation and the information in the table, what is the enthalpy of the reaction?
Use Delta H r x n equals the sum of delta H f of all the products minus the sum of delta H f of all the reactants..
–453.46 kJ
–226.73 kJ
226.73 kJ
453.46 kJ
To calculate the enthalpy of the reaction, we need to use the standard enthalpies of formation given in the table.
Reactants:
2C (s, graphite) = 2(0 kJ/mol) = 0 kJ/mol
H2 (g) = 0 kJ/mol
Products:
C2H2 (g) = 226.73 kJ/mol
ΔH rxn = ΣΔHf(products) - ΣΔHf(reactants)
ΔH rxn = 226.73 kJ/mol - (0 kJ/mol + 0 kJ/mol)
ΔH rxn = 226.73 kJ/mol
Therefore, the enthalpy of the reaction is 226.73 kJ.