Hess' Law?

2016-03-01 11:18 am
Given the following data:

2C(s) + H2(g) --> C2H2(g)
delta H° = 227.0 kJ

C2H2(g) + 5/2O2(g) --> 2CO2(g) + H2O(l)
delta H° = -1300.0 kJ

CO2(g) --> C(s) + O2(g)
delta H° = 393.5 kJ

Calculate delta H° for the reaction
H2O(l) --> H2(g) + 1/2O2(g)

Please help, I'm stuck :( thank you

回答 (1)

2016-03-01 1:20 pm
✔ 最佳答案
C₂H₂(g) →2C(s) + H₂(g) .... ΔH° = -227.0 kJ
2CO₂(g) + H₂O(l) → C₂H₂(g) + (5/2)O₂(g) .... ΔH° = +1300.0 kJ
2C(s) + 2O2(g) → 2CO₂ .... ΔH° = 2×(-393.5) kJ

Add the above three thermochemical equations, and cross out C₂H₂(g), 2C(s), 2CO₂(g) and 2O₂(g) on the both sides. Then,
H₂O(l) → H₂(g) + (1/2)O₂(g) .... ΔH° = -227 + 1300 + 2×(-393.5) = +286 kJ


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