Quick way

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Selena Yu 1H
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Joined: Fri Aug 09, 2019 12:16 am

Quick way

Postby Selena Yu 1H » Sun Jan 12, 2020 1:30 pm

Why is the quick way to know whether or not the reaction shifts to the right or left for change in pressure not exactly correct according to Dr. Lavelle?

romina_4C
Posts: 100
Joined: Thu Jul 11, 2019 12:17 am

Re: Quick way

Postby romina_4C » Sun Jan 12, 2020 1:39 pm

If the volume decreases (pressure increases), the reaction will shift to the side with less moles of a gas. For example, if you had 3 moles of reactants and 2 moles of products and the pressure increased, the reaction would shift to the right since there are fewer moles of gas. If the volume increased (pressure decreased), the reaction would shift to the side with more moles of gas. As per the example above, if the pressure decreased, the reaction would shift to the left.

Wilson 2E
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Joined: Sat Aug 17, 2019 12:18 am

Re: Quick way

Postby Wilson 2E » Sun Jan 12, 2020 1:46 pm

The example Dr. Lavelle gave in class was if you added Helium to a reaction occurring within a sealed container. While the pressure of the reaction is increasing, it has no effect on the equilibrium because adding gas doesn't have any effect on the actual concentration of either the products or reactants. So while a change in pressure that changes volume as well (compression) would change the equilibrium, a change in only pressure does not.

DLee_1L
Posts: 103
Joined: Sat Aug 17, 2019 12:17 am

Re: Quick way

Postby DLee_1L » Fri Jan 17, 2020 9:46 am

Wilson 2E wrote:The example Dr. Lavelle gave in class was if you added Helium to a reaction occurring within a sealed container. While the pressure of the reaction is increasing, it has no effect on the equilibrium because adding gas doesn't have any effect on the actual concentration of either the products or reactants. So while a change in pressure that changes volume as well (compression) would change the equilibrium, a change in only pressure does not.

But does a change in pressure always result in a change in volume? PV=nrT? Or do you mean that the change in pressure must always occur due to a change in volume?

Shutong Hou_1F
Posts: 117
Joined: Sat Sep 14, 2019 12:17 am

Re: Quick way

Postby Shutong Hou_1F » Fri Jan 17, 2020 11:40 pm

DLee_1L wrote:
Wilson 2E wrote:The example Dr. Lavelle gave in class was if you added Helium to a reaction occurring within a sealed container. While the pressure of the reaction is increasing, it has no effect on the equilibrium because adding gas doesn't have any effect on the actual concentration of either the products or reactants. So while a change in pressure that changes volume as well (compression) would change the equilibrium, a change in only pressure does not.

But does a change in pressure always result in a change in volume? PV=nrT? Or do you mean that the change in pressure must always occur due to a change in volume?


A change in pressure always result in a change in volume, if temperature and number of molecules don't change. The underlying reason why changing volume/pressure could result in shift of a reaction is that the concentrations would change, whereas temperature doesn't change, so equilibrium constant doesn't change.

905373636
Posts: 62
Joined: Thu Aug 01, 2019 12:15 am

Re: Quick way

Postby 905373636 » Sat Jan 18, 2020 11:22 am

Shutong Hou_1F wrote:
DLee_1L wrote:
Wilson 2E wrote:The example Dr. Lavelle gave in class was if you added Helium to a reaction occurring within a sealed container. While the pressure of the reaction is increasing, it has no effect on the equilibrium because adding gas doesn't have any effect on the actual concentration of either the products or reactants. So while a change in pressure that changes volume as well (compression) would change the equilibrium, a change in only pressure does not.

But does a change in pressure always result in a change in volume? PV=nrT? Or do you mean that the change in pressure must always occur due to a change in volume?


A change in pressure always result in a change in volume, if temperature and number of molecules don't change. The underlying reason why changing volume/pressure could result in shift of a reaction is that the concentrations would change, whereas temperature doesn't change, so equilibrium constant doesn't change.


So, Volume here doesn't change as []s are rising in proportion to Pressure?

Sofia Barker 2C
Posts: 101
Joined: Wed Sep 18, 2019 12:21 am

Re: Quick way

Postby Sofia Barker 2C » Sun Jan 19, 2020 12:10 pm

Changing the pressure of a reaction by adding an inert gas has no effect on the concentrations of reactants or products, so the quick way of determining equilibrium shifts doesn't apply. You just need to make sure that the change in pressure causes a change in volume, because that is how concentrations change.

Robert Tran 1B
Posts: 118
Joined: Thu Jul 11, 2019 12:15 am

Re: Quick way

Postby Robert Tran 1B » Sun Jan 19, 2020 1:00 pm

When the pressure increases, the reaction will shift to the side that produces less moles of gas. Conversely, when the pressure decreases, the reaction will shift to the side that produces more moles of gas.


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