Step 1 of a process has delta H = -90 kJ and step 2 has delta H = -110 kJ. By Hess's law, what is the overall delta H?
Answer and explanation
Correct answer: C. -200 kJ
- Step 1: Hess's law says the overall enthalpy change is the sum of the steps.
- Step 2: delta H = -90 + (-110) = -200 kJ.
Answer
-200 kJ.
Why not the others: '20 kJ' subtracts the second enthalpy change instead of adding it; '200 kJ' reverses the sign of the total; '99 kJ' multiplies the enthalpy changes.
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