Temperature Units


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Mya Majewski 1L
Posts: 89
Joined: Fri Sep 25, 2015 3:00 am

Temperature Units

Postby Mya Majewski 1L » Thu Jan 10, 2019 5:57 pm

How do you know whether to use K=273 K (STP) or K=298 K when calculating PV=nRT?

Michael Torres 4I
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Re: Temperature Units

Postby Michael Torres 4I » Thu Jan 10, 2019 5:58 pm

I believe Lavelle mentioned in one of the modules that the temperature will be given to you. You will not have to assume which is correct.

Shubham Rai 2C
Posts: 64
Joined: Fri Sep 28, 2018 12:27 am

Re: Temperature Units

Postby Shubham Rai 2C » Thu Jan 10, 2019 6:01 pm

The temperature will be unique for each of the problems as reactions can take place at different temperatures and the Kc value is also affected by the temperature thus each reaction will have a unique value of K (Kelvin).

Mya Majewski 1L
Posts: 89
Joined: Fri Sep 25, 2015 3:00 am

Re: Temperature Units

Postby Mya Majewski 1L » Thu Jan 10, 2019 6:05 pm

Even though gases use STP at 273K it will primarily depend on the question? Or you just have to know if you're given gases to use 273K?

Michael Torres 4I
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Re: Temperature Units

Postby Michael Torres 4I » Thu Jan 10, 2019 6:20 pm

I think it depends on what the question gives you. For example, take a look at 5H.3 in the seventh edition. It specifically asks you to take into consideration the equilibrium constants for reactions occurring at 300K, despite the fact that all the products and reactants in the reactions are gases. When you look at the table it asks you to reference, you will see that it (Table 5G.2) gives you values for equilibrium constants for a variety of reactions that occur exclusively between gases. These reactions vary in their temperatures. Some occur at 300K, 500K, 1000K, or other temperature values.

As such, I think you should try to see which values for temperature the question is giving you rather than primarily relying on STP conditions. However, it very well could occur that a question may ask specifically for STP conditions, so my advice is basically to just be aware of the specific details the question provides before assuming the reaction takes place at STP.


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