Review Of Chemical Equilibrium Concepts

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When a reaction is at equilibrium, the CONCENTRATION of both reactants and products remains unchanged.
HOWEVER, at the molecular level when a reaction reaches equilibrium, reactants form products, and products form reactants at an EQUAL rate.
Under the same conditions, the same reaction at equilibrium will ALWAYS have the same product concentration to the reactant concentration ratio, which is equivalent to the equilibrium constant.

K= [P]\[R] IS THE EQUATION TO CALCULATE THE EQUILIBRIUM CONSTANT. ***Remember that the equilibrium constant is the constant that is equivalent to the ratio of product concentration to reactant concentration at equilibrium.***

If you calculate a LARGE K value, then you can deduce that there is a lot of product being made in the reaction. Generally, if K is larger than 1,000 (for our class)
If you calculate a SMALL K value, then you can expect that a small amount of product will be present at equilibrium, whereas there will be a large amount of reactant. Generally, K=0.001 or smaller (for our class).
You may be asking, what happens if K is between these two numbers? Well, in that case, you can tell if products or reactants are favored slightly by how close or far it is from either end of the spectrum, but overall, you can say that neither product nor reaction formation is highly favored!
ALSO! If K is exactly equal to one, this is very rare, but it means that the reactants and products have the same exact concentration at equilibrium. This is unlikely to happen however due to the varying structures and stability that molecules possess.

-When plugging into the equilibrium constant equation, it is important to remember that you must ensure that your reference equation is BALANCED so that you use the correct stoichiometric coefficients, which each product and reactant are then raised to within the ratio.
-You must also not include units!
-You must also ensure that you are plugging in the CONCENTRATION of products and reactants, so you must find their MOLARITY! Do not use moles in liu of molarity because unless the reaction takes place in one liter, you will get the wrong answer! Make sure you calculate Molarity= moles/liter before plugging into the equilibrium constant equation!
-If the FORWARD RXN equilibrium constant is equal to K, then the REVERSE RXN is equal to 1/K! The problem statement will make it clear whether the RXN is occurring in the forward or reverse RXN.
-DO NOT include liquids or solids in your calculation of the equilibrium constant! Only gases are relevant to the calculation. You may therefore find that you will express the K ratio as 1/ Reactants, as there may be no product in the gaseous form, and you may also have to express the ratio as P/1 because again, you may not have any reactants in the gaseous state in that specific RXN! This is because their molar concentrations remain relatively unchanged!

If a RXN is considered to be HOMOGENOUS, then all P and R are in the same phase at equilibrium
If a RXN is said to be HETEROGENOUS, then one or more products and/or reactants are in different phases at equilibrium.

For a gas, we use partial pressure! The equilibrium constant is just K subscript p, but the calculation is the same as the equilibrium constant discussed above!
You CAN CONVERT between partial pressure and molar concentration using the equation PV=nRT where P=pressure, V= volume, n= number of moles, T=temperature, and R= the gas constant for the gas (but you will be given R in the problem statement!)

[ella3]

Thank you this is such a good summary of what we've covered!

[Gabrielle Linden 1C]

This is so insanely helpful! Thank you so much!