Equilibrium shift by pressure

Michael Du 1E
Posts: 117
Joined: Sun Sep 22, 2019 12:16 am

Equilibrium shift by pressure

What are the rules for the equilibrium shift by the change of pressure? Will the change of pressure only affect the equilibrium if the pressure change is caused by a change in volume? I believe I heard from somewhere that there will not be a shift in the equilibrium if only pressure is changed. Thank you.

Ayushi2011
Posts: 101
Joined: Wed Feb 27, 2019 12:17 am

Re: Equilibrium shift by pressure

If the system is compressed, the reaction proceeds in the direction with the least moles of the gas, which can be either reactants or products.

kim 2I
Posts: 105
Joined: Thu Jul 25, 2019 12:17 am

Re: Equilibrium shift by pressure

When the volume decreases (increase in pressure), the reaction will shift to where there are less moles of gas.
When the volume increases (decrease in pressure), the reaction will shift to where there are more moles of gas.

Manav Govil 1B
Posts: 104
Joined: Sat Sep 07, 2019 12:19 am

Re: Equilibrium shift by pressure

The inverse is also true. If the pressure is decreased (more volume available in the system), the equilibrium will shift towards the side that has more moles.

Sanjana Borle 2K
Posts: 111
Joined: Fri Aug 09, 2019 12:15 am

Re: Equilibrium shift by pressure

The equilibrium constant does not change with pressure.

Manav Govil 1B
Posts: 104
Joined: Sat Sep 07, 2019 12:19 am

Re: Equilibrium shift by pressure

Equilibrium constant does not change (it only changes if temperature changes), but the equilibrium will shift in such a way that the equilibrium constant remains the same after calculation.

Orrin Zhong 4G
Posts: 51
Joined: Sat Jul 20, 2019 12:16 am

Re: Equilibrium shift by pressure

That is correct. The equilibrium shift only occurs when the volume is changed (assuming there are gases participating in the reaction), since the partial pressures of the reactants and products will change, modifying their values in the equilibrium calculations. However, if the total pressure is changed while the volume is held constant (such as when an inert gas is pumped into the system), the individual partial pressures of each species is not changed and therefore no equilibrium shift will occur.

Hope Hyland 2D
Posts: 50
Joined: Wed Feb 20, 2019 12:16 am

Re: Equilibrium shift by pressure

Yes, the equilibrium shift only occurs if the pressure changes due to changes in volume. For example, if a gas is compressed, or the volume is decreased, then the pressure increases and equilibrium shifts to the direction with less moles.

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