Step 1 of a process has delta H = -286 kJ and step 2 has delta H = -393 kJ. By Hess's law, what is the overall delta H?
Answer and explanation
Correct answer: B. -679 kJ
- Step 1: Hess's law says the overall enthalpy change is the sum of the steps.
- Step 2: delta H = -286 + (-393) = -679 kJ.
Answer
-679 kJ.
Why not the others: '107 kJ' subtracts the second enthalpy change instead of adding it; '679 kJ' reverses the sign of the total; '1123 kJ' multiplies the enthalpy changes.
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