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### Changes in Pressure

Posted: Sat Jan 11, 2020 2:29 pm
During Dr.Lavelle's last lecture he mentioned that changes in pressure does not necessarily cause a forward or reverse reaction to be favored. Instead, he said that it all relies on changes in concentration not change in pressure. Can someone please explain this?

### Re: Changes in Pressure

Posted: Sat Jan 11, 2020 2:48 pm
I think he was talking about how if the pressure is increased for a particular reaction, it isn't an adequate explanation to say that it will cause a shift to the right because there are more moles of reactants than products. Instead, the correct explanation would be that an increase in pressure would mean a decrease in volume (due to PV=nRT), which means the initial concentration increases, and the reaction shifts right.

### Re: Changes in Pressure

Posted: Sat Jan 11, 2020 4:20 pm
I think it's the fact that it isn't just a change of pressure will change whether a reaction will be forward of in reverse, it's more of how has the pressure changed and if there are any other modified factors.

### Re: Changes in Pressure

Posted: Sat Jan 11, 2020 4:33 pm
It has to do with the equation C=n/V. This equation shows that if the volume is changed then the concentrations also change. For example, when the volume is halved and the pressure is doubled, the concentration of the reactants and products changes. This causes the reaction to no longer be at equilibrium, and will, therefore, have to favor either the reactants or the products in order to go back to equilibrium. Therefore, although the pressure and volume are changed, it is the change in concentrations that causes either the reactants or products to be favored as the system is no longer in equilibrium.