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Units of ΔS

Posted: Sat Feb 03, 2018 9:21 pm
by RyanTran2F
Why does the answer key sometimes solve for ΔS and say units is J/K but sometimes J/K mol? When do we add on the "per mole" and will we be marked down if we do not have it? Thanks :)

Re: Units of ΔS

Posted: Sat Feb 03, 2018 10:38 pm
by Gianna Apoderado 1B
From what I’ve seen, delta S is given in both J/K and J/K•mol-1 depending on the context of what you need it for! (Ive always assumed that the “per mole” is implied)

Re: Units of ΔS

Posted: Sun Feb 04, 2018 9:53 am
by Shawn Patel 1I
Hey,
If J/k mol is given for enthalpy, and there is no value of mol that needs to be accounted for, then the entropy would also be in J/k mol. In some cases, such as when calculating standard reaction entropy, and you are given the amount of moles per product or reactant, then the answer would likely come out as J/k.

Re: Units of ΔS

Posted: Sun Feb 04, 2018 11:36 am
by RyanTran2F
Shawn Patel 1I wrote:Hey,
If J/k mol is given for enthalpy, and there is no value of mol that needs to be accounted for, then the entropy would also be in J/k mol. In some cases, such as when calculating standard reaction entropy, and you are given the amount of moles per product or reactant, then the answer would likely come out as J/k.


Well that was what I thought but when the answer key calculates standard reaction entropy, the answer has a per mole. When it uses qrev/T then it is just J/K. Thanks :)