ThermochemistryHard
Question
From the following data at 25o C, which of the following statement(s) is/are correct?
½H2(g) + ½O2(g)→ OH(g): ΔHo = 42 kJ
H2(g) + ½O2(g) → H2O(g): ΔHo = −242 kJ
H2(g) → 2H(g): ΔHo = 436 kJ
O2(g) →2O(g): ΔHo = 495 kJ
Options
A.ΔrHo for the reaction H2O(g) → 2H(g) + O(g) is 925.5 kJ.
B.ΔrHo for the reaction OH(g) → H(g) + O(g) is 502 kJ.
C.Enthalpy of formation of H(g) is −218 kJ/mol.
D.Enthalpy of formation of OH(g) is 42 kJ/mol.
Solution
$(a)\Delta_{r}H = \left( 436 + \frac{1}{2} \times 495 \right) - ( - 242) = 925.5\text{ kJ}$
$(b)\Delta_{r}H = \left( \frac{1}{2} \times 436 + \frac{1}{2} \times 495 \right) - ( - 42) = 423.5\text{ kJ} $$${(c)\Delta_{r}H_{H(g)} = \frac{1}{2} \times 436 = 218\text{ kJ/mol} }{(d)\Delta_{f}H_{OH(g)} = 42\text{ kJ/mol}}$$
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