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Partial pressure vs pressure

Posted: Mon Jan 21, 2019 2:16 pm
by Jane Burgan 1C
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?

Re: Partial pressure vs pressure

Posted: Mon Jan 21, 2019 2:23 pm
by Madeline Ho 1C
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.

Re: Partial pressure vs pressure

Posted: Mon Jan 21, 2019 2:31 pm
by Jayasuriya Senthilvelan 4I
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.