Units  [ENDORSED]

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Cindy Ngo 1E
Posts: 14
Joined: Fri Jul 22, 2016 3:00 am

Units

Postby Cindy Ngo 1E » Wed Jan 18, 2017 10:21 am

How do you know when the units are kj or kj/mol?

Alyssa Ishimoto 1A
Posts: 10
Joined: Sat Jul 09, 2016 3:00 am

Re: Units

Postby Alyssa Ishimoto 1A » Wed Jan 18, 2017 10:28 am

You must always use kJ/mole for standard enthalpy of formation because it is the formation of 1 mole of a compound from its elements. But you can use KJ for reaction enthalpy.

Elias Ruben 1O
Posts: 47
Joined: Wed Sep 21, 2016 2:56 pm

Re: Units  [ENDORSED]

Postby Elias Ruben 1O » Wed Jan 18, 2017 10:30 am

Generally, the enthalpy you solve for in a problem will be in kJ. However, it can vary depending on the what the problem asks for. For example, if it asks you to find the standard enthalpy of formation, it will be in kJ/mol since standard enthalpy of formation is in kJ/mol by definition. Pay attention to the wording of the problem and you'll know what to do.

Manali Ghadiali 1E
Posts: 21
Joined: Sat Jul 09, 2016 3:00 am

Re: Units

Postby Manali Ghadiali 1E » Wed Jan 18, 2017 10:37 am

Usually, the chemical reaction is in kj because each reaction has a varying ratio and number of moles. The question can ask, however, what the change per mole is for either the product or reactant. In that case, divide the kj quantity accordingly to find kj/mol.

samuelkharpatin2b
Posts: 55
Joined: Wed Sep 21, 2016 2:57 pm

Re: Units

Postby samuelkharpatin2b » Wed Jan 18, 2017 6:38 pm

Most of the time when working with reaction enthalpy problems the units will be in kJ. However, if a question contains wording such as "enthalpy per mole" or something of that sort, the answer will be in kJ/mol. Answers are in kJ/mol when working with standard enthalpies of formation, always.

Gigi Ye 2K
Posts: 9
Joined: Wed Sep 21, 2016 2:55 pm

Re: Units

Postby Gigi Ye 2K » Thu Jan 19, 2017 10:40 am

The units would most likely be in kJ instead of kJ/mole. When multiplying the different enthalpies, the moles unit cancel out.


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