What is the change in enthalpy (delta H) for this reaction?
C4H4 (g) + 2(H2) (g) => C4H8 (g)
Given:
Enthalpies of combustion for:
C4H4 (g) = -2341 kJ/mol
H2 (g) = -286 kJ/mol
C4H8 (g) = -2775 kJ/mol
The right answer is supposed to be -158kJ/mol.
Please show me how to solve a problem like this.
How I tried to solve it:
Normally you solve these types of problems given the enthalpies of formation, as C4H8 is being formed.
Assuming the enthalpy of formation is the reverse of the enthalpy of combustion, so multiply combustions by -1 to get formations (I'm not sure if this is right).
delta H = sum enthalpies products - sum enthalpies reactants
= (2775) - [2(286) + 2341]
= -138 kJ/mol
Other way I tried to solve it. C4H4 is being combusted to CO2 and H2O, and 2H2 is being combusted to 4H. C4H8 is formed from the products of combustion, so
2775 - 2(286) - 2341 = -138 kJ/mol
^
Reverse for formation
C4H4 (g) + 2(H2) (g) => C4H8 (g)
Given:
Enthalpies of combustion for:
C4H4 (g) = -2341 kJ/mol
H2 (g) = -286 kJ/mol
C4H8 (g) = -2775 kJ/mol
The right answer is supposed to be -158kJ/mol.
Please show me how to solve a problem like this.
How I tried to solve it:
Normally you solve these types of problems given the enthalpies of formation, as C4H8 is being formed.
Assuming the enthalpy of formation is the reverse of the enthalpy of combustion, so multiply combustions by -1 to get formations (I'm not sure if this is right).
delta H = sum enthalpies products - sum enthalpies reactants
= (2775) - [2(286) + 2341]
= -138 kJ/mol
Other way I tried to solve it. C4H4 is being combusted to CO2 and H2O, and 2H2 is being combusted to 4H. C4H8 is formed from the products of combustion, so
2775 - 2(286) - 2341 = -138 kJ/mol
^
Reverse for formation
