PhyChem - Thermodynamics

2012-10-02 1:15 am

At a specific set of conditions, 241.8kJ is given off when 1 mol of H2O(g) forms from its elements. Under the same conditions, 285.8kJ is given off when 1 mol of H2O(l) forms from its elements. Calculate the heat of vaporization of water at these conditions. (5%)

I don't know how to calculate this question, please help me.

回答 (1)

老爺子

2012-10-02 4:47 am

✔ 最佳答案

Given :
H2(g) + (1/2)O2(g) → H2O(g) ... ΔH = -241.8 kJ/mol
H2(g) + (1/2)O2(g) → H2O(l) ... ΔH = -285.8 kJ/mol

Reverse the second thermochemical equation. Then,
H2(g) + (1/2)O2(g) → H2O(g) ... ΔH = -241.8 kJ/mol
H2O(l) →H2(g) + (1/2)O2(g) ... ΔH = +285.8 kJ/mol

Add the two thermochemical equation together, and cancel H2(g) and(1/2)O2(g) on the both sides :
H2O(l) → H2O(g) ... ΔH= -241.8 + 285.8 = +44 kJ/mol

Hence, the heat of evaporation of water at these conditions = +44kJ/mol

參考: 老爺子

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