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Changes in pressure

Posted: Sun Jan 12, 2020 3:32 pm
by JamieVu_2C
I know that the quick way to explain the changes in pressure is that if the volume decreases and there are more moles of gas on the left, then the reaction proceeds to the right and vice versa. But why is this the short way? If you know that the volume decreases, then you also know that there is still a larger concentration of the moles of gas in the container, so more products will be formed to lessen that pressure at equilibrium. Within the short way of explaining the change in pressure, isn't concentration already implied in the explanation?

Re: Changes in pressure

Posted: Sun Jan 12, 2020 4:20 pm
by 805394719
When we consider a change in pressure, we assume a constant concentration of the reactants even though the volume has changed. When you increase the pressure, the volume decreases, and so there will be the same amount of reactants as there were in the first place but the volume they occupy has decreased so if they will be contained within a narrower space and this will increase the pressure. When you decrease the pressure, the volume increases, so there will be the same amount of reactants in a bigger space so this will decrease their pressure. Thinking of volume for a change of pressure is easier because the effect of pressure is based on its implication of a change in volume which gives the reactants less space to escape and thus forces them together to react. The concentration remains the same throughout the changes until the system balances itself.

Re: Changes in pressure

Posted: Sun Jan 12, 2020 7:33 pm
by Jesse H 2L
JamieVu_2C wrote:I know that the quick way to explain the changes in pressure is that if the volume decreases and there are more moles of gas on the left, then the reaction proceeds to the right and vice versa. But why is this the short way? If you know that the volume decreases, then you also know that there is still a larger concentration of the moles of gas in the container, so more products will be formed to lessen that pressure at equilibrium. Within the short way of explaining the change in pressure, isn't concentration already implied in the explanation?



Also, we only recognize a change in pressure IF it is the direct result of a change in volume. Pumping a closed system full of an inert gas will not effect the equilibrium.

Re: Changes in pressure

Posted: Mon Jan 13, 2020 7:12 pm
by alicechien_4F
The way I learned the "easy" way in high school was that the gas wants to go into the area with more space so that it can expand. That is why the reaction will proceed towards the side with less moles, since there is more area for the gas.

Re: Changes in pressure

Posted: Tue Jan 14, 2020 9:14 am
by Joowon Seo 3A
If we change the volume so that the pressure increases, the concentration of the products and reactants changes, so more reactions happen to keep it at the equilibrium constant.