Shift Change Rules

[Gabriel Ordonez 2K]

Can someone list all the required shift change rule scenarios that Lavelle would want us to know?

[Venus_Hagan 2L]

Add products or remove reactants → toward reactants
Add reactants or remove products → toward products
if you inc pressure, then shifts toward fewer gas particles
if you dec pressure, then shift toward more gas particles
For exothermic reactions: inc temp → toward reactants
dec temp → toward products
For endothermic reactions: inc temp → toward products
dec temp → toward reactants
Q < K → toward products
Q > K → toward reactants
Q = K → at equilibrium

[Gabriel Ordonez 2K]

Thank you for the reply, this clarifies a lot for the shift changes. In terms of Q, this makes sense, how about for all the different Le Chatellier’s Principles.

[Amy Pham 1D]

Thank you for the reply, this clarifies a lot for the shift changes. In terms of Q, this makes sense, how about for all the different Le Chatellier’s Principles.

Le Chatelier's Principle effectively states that systems adjust so as to minimize the effect of any changes. Adhering to this simple rule will explain all the shifts that occur due to all the various changes to conditions as listed above. Adding or removing products/reactants would cause shifts to use up/create more substance according to the change, changing pressure (through volume) results in different concentrations and thus shifts to counteract this, and changing temperature changes the internal energy of a system and thus the rate of reactions either forwards or backwards.
Overall, just keep in mind the principle that systems shift to counteract changes!

[Brian Tangsombatvisit 1C]

Some extra things to remember: when heating an endothermic reaction, the K of the reaction permanently increases; conversely when heating an exothermic reaction, the K of the rxn permanently decreases. Also, when determining reaction shifts according to changes in pressure (and the rxn involves gases) make sure that the concentrations of the reactants and/or products are actually changing, since this is what shifts equilibrium. If you add in inert/noble gases into the sample, the pressure of the sample also increases, but equilibrium doesn't shift since the concentrations of the reactants and products didn't change. Their concentrations would change, however, as a result of compression or addition/removal.

[Kavya Immadisetty 2B]

You should know how an equilibrium shifts when concentrations of species are changed, temperature is changed, or when pressure is changed