Hess’ Law Question, Calculating Enthalpy Change?
I have a question regarding Hess's Law and calculating enthalpy change.
I need to calculate the standard enthalpy change for the following reaction:
2 HCl (g) + F2 (g) → 2 HF (l) + Cl2 (g)
Given the following reactions:
1) 4 HCl (g) + O2 (g) → 2 H2O (l) + 2 Cl2 (g), ΔH = -202.4 kJ/mol 2) (1/2) H2 (g) + (1/2) F2 (g) → HF (l), ΔH = -600 kJ/mol 3) H2 (g) + (1/2) O2 (g) → H2O (l), ΔH = -285.8 kJ/mol
To approach this, I multiplied the first reaction by 1/2 and the second reaction by 2. This gives me the following equations:
2 HCl (g) + (1/2) O2 (g) → H2O (l) + Cl2 (g), ΔH = -101.2 kJ/mol H2 (g) + F2 (g) → 2 HF (l), ΔH = -1200 kJ/mol H2 (g) + (1/2) O2 (g) → H2O (l), ΔH = -285.8 kJ/mol
After calculating, I arrived at an answer of -1587 kJ/mol for the reaction, but it seems to be incorrect.
Could someone help me identify my mistake and guide me on how to correct it? Thank you!
3 Answers
Feb 21, 2025
you end up subtracting the last line of reactions because if you add that, your result ends up having H2, O2, and H2O
so your answer should be -1015.4 kJ/mol
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