Partial pressure vs pressure

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Jane Burgan 1C
Posts: 73
Joined: Fri Sep 28, 2018 12:15 am

Partial pressure vs pressure

Postby Jane Burgan 1C » Mon Jan 21, 2019 2:16 pm

Is there a difference when the question asks what happens to the equilibrium composition if the partial pressure of one reactant is increased versus if the overall pressure is increased?

Madeline Ho 1C
Posts: 37
Joined: Mon Apr 23, 2018 3:00 am

Re: Partial pressure vs pressure

Postby Madeline Ho 1C » Mon Jan 21, 2019 2:23 pm

With partial pressure, you treat the equilibrium composition the same as you would a change in concentration. If the partial pressure of something is increased on the products' side, for example, the reaction will shift towards the reactants. An overall increase in pressure usually is in response to a decrease in volume. The quick way to tell which way the reaction will shift is to look at the number of moles of gas on each side. The reaction will shift towards the side with fewer moles if volume decreases/pressure increases.

Jayasuriya Senthilvelan 4I
Posts: 31
Joined: Thu Jan 10, 2019 12:17 am

Re: Partial pressure vs pressure

Postby Jayasuriya Senthilvelan 4I » Mon Jan 21, 2019 2:31 pm

I agree with the above. Partial pressure changes can be treated the same as changes in the concentration of a specific reactant. However, changes in the overall pressure of the system (due to a change in the volume), is a little different. You have to determine the direction of the reaction that is favored by counting the number of moles on each side of the reaction.

Also, it is also important to note that if one changes the pressure of a system by including some inert gas, then there is no change in the reaction direction.

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