Hess Law

6/25/2018 7:13:27 PM
I have a question about the passage about Hess's Law. I thought Hess's Law was defined as the sum of the standard molar enthalpies for the products minus the sum of the standard molar enthalpies of the reactants.

In this question, the answer states, "Hess law states that the overall enthalpy change of a reaction is equal to the sum of the enthalpies of formation for each component. Because reactants are consumed rather than formed, the signs of their enthalpies must be changed."

I understand this, but shouldn't it be -55 = (2NaOH + 140) - [2(350) + 45]? I would appreciate if this could be explained.
edited by on 6/26/2018


6/27/2018 7:41:53 PM
Could you attach an image of question you are talking about?


6/29/2018 3:44:18 PM
vtfu708444 wrote:
I have a question about the passage about Hess's Law. I thought Hess's Law was defined as the sum of the standard molar enthalpies for the products minus the sum of the standard molar enthalpies of the reactants.

In this question, the answer states, "Hess law states that the overall enthalpy change of a reaction is equal to the sum of the enthalpies of formation for each component. Because reactants are consumed rather than formed, the signs of their enthalpies must be changed."

I understand this, but shouldn't it be -55 = (2NaOH + 140) - [2(350) + 45]? I would appreciate if this could be explained.
edited by on 6/26/2018


Hi there,
We saw your post here as well as your feedback on the question itself. The explanation has been updated to further explain how to get to the correct answer. Please take a look at the updated explanation. Thanks!


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