Quick way

[Selena Yu 1H]

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]

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]

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]

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]

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]

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]

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]

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.