### 4D.23

Posted:

**Wed Feb 12, 2020 3:19 pm**Why do you need to subtract twice the enthalpy of formation of NO to get the total reaction enthalpy?

Created by Dr. Laurence Lavelle

https://lavelle.chem.ucla.edu/forum/

https://lavelle.chem.ucla.edu/forum/viewtopic.php?f=76&t=59308

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Posted: **Wed Feb 12, 2020 3:19 pm**

Why do you need to subtract twice the enthalpy of formation of NO to get the total reaction enthalpy?

Posted: **Wed Feb 12, 2020 4:00 pm**

Because there are two moles of NO gas. Standard enthalpies of formation are given per mole, so you need to multiply each one by the number of moles when using the equation given on the formula sheet.

Posted: **Sun Feb 16, 2020 10:28 pm**

We subtract twice the value because it is asking for the total reaction enthalpy and there are 2 mol of NO. If was asking for the enthalpy for the formation of 1 mol, then the initial value would be your answer.