Standard State

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Ethan Vuong 3G
Posts: 51
Joined: Fri Sep 29, 2017 7:07 am

Standard State

Postby Ethan Vuong 3G » Sat Feb 10, 2018 2:58 pm

How does whether it is standard state or not affect the change in enthalpy or entropy? What is its significance?

Luke Bricca 1H
Posts: 30
Joined: Fri Sep 29, 2017 7:06 am

Re: Standard State

Postby Luke Bricca 1H » Sat Feb 10, 2018 3:01 pm

Standard state refers to the standard temperature and pressure of a substance, and altering either affects both entropy and enthalpy if you look at the equations used to calculate both.

Maria Bajenov 1I
Posts: 28
Joined: Fri Sep 29, 2017 7:06 am

Re: Standard State

Postby Maria Bajenov 1I » Sat Feb 10, 2018 3:31 pm

If it is not in standard state, the values of deltaH differ because the temperature it is carried out at is not the temperature at which deltaH was measured. Therefore, the problem must be done in parts, separating the different temperatures and then combining all the values from each separate calculation for overall enthalpy. In the book. it gives the example of vaporizing water at 25 Celcius. First, heat the liquid to its normal boiling point at 100 Celcius, then allow it to vaporize, then cool the vapor back to 25 Celcius. Each stage occurs at a different temperature and must be separated.

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