## Enthalpy of Rxn

eduardomorales5
Posts: 77
Joined: Fri Aug 30, 2019 12:15 am

### Enthalpy of Rxn

If the enthalpy of a reaction is 300kJ/mol, and we have 0.05mol of th substance, do we multiply or divide by the moles of the substance to find the enthalpy of the reaction?

Haley Dveirin 1E
Posts: 101
Joined: Sat Jul 20, 2019 12:17 am

### Re: Enthalpy of Rxn

Multiply

Sofia Ban
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Joined: Fri Sep 28, 2018 12:25 am

### Re: Enthalpy of Rxn

You would multiply 300kJ/mol by the 0.05 mol since we are trying to get rid of the mol unit. Keep in mind we are trying to find the enthalpy of the reaction which the units are in joules.

preyasikumar_2L
Posts: 101
Joined: Fri Aug 09, 2019 12:17 am

### Re: Enthalpy of Rxn

You multiply 300kJ/mol by 0.05 mol to get the mol units to cancel out and get a result of 15 kJ for the enthalpy of reaction.

Posts: 125
Joined: Sat Aug 17, 2019 12:17 am

### Re: Enthalpy of Rxn

eduardomorales5 wrote:If the enthalpy of a reaction is 300kJ/mol, and we have 0.05mol of th substance, do we multiply or divide by the moles of the substance to find the enthalpy of the reaction?

Usually if I'm stuck on deciding whether not to multiply or divide I look at the units. Think about what units you want in the end and the units that you have now. Think about how you can manipulate the two to cancel, resulting in the units you want.

In your case, you would multiply.

Kate Swertfager
Posts: 50
Joined: Wed Sep 18, 2019 12:17 am

### Re: Enthalpy of Rxn

Multiply. Also always look at the units for help. You need moles to cancel

Emily Burghart 1k
Posts: 50
Joined: Wed Sep 18, 2019 12:17 am

### Re: Enthalpy of Rxn

$\frac{300 kJ}{mol} \cdot .05 mol= kJ$

As you can see here, you will want to multiply the values to cancel out the mol, so you are left with kJ. You are left with 15kJ.

Anokhi Patel 2B
Posts: 76
Joined: Fri Aug 09, 2019 12:17 am

### Re: Enthalpy of Rxn

you just multiply the enthalpy of the reaction by the moles to cancel out the reaction

Alexandra Bartolome 2H
Posts: 102
Joined: Sat Jul 20, 2019 12:17 am

### Re: Enthalpy of Rxn

You would multiply so that the moles cancel out and you are left with the units kJ.

Bryan Chen 1H
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Joined: Mon Jun 17, 2019 7:24 am

### Re: Enthalpy of Rxn

i personally dont think about multiplying or dividing, i look at the units of each (kJ, and kJ/mole), and i try to format it so the units cancel. i think its called dimensional analysis or something

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