Unit 3: Equilibrium by Mary Grace

Key Concepts

marygracebunch2 — 2017-01-04 14:18:07 UTC

Le Chatlier's Principle
Interpreting K
Comparing Q and K
Manipulating equilibrium expressions (coefficient rule, reciprocal rule, and multiple equilibria rule)
To find equilibrium concentrations given Kc or Kp, remember using ICE charts!
Rate laws (Learned these in Kinetics Unit, be able to draw upon previous knowledge)

Definitions

marygracebunch2 — 2017-01-04 14:18:23 UTC

Le Chatlier Principle: if a “stress” is added to a system already at equilibrium, the equilibrium will shift so as to relieve the “stress”
Q = rxn quotient :

Q measures the relative amounts of products and reactants present during a reaction at a particular point in time (not at equilibrium) As a rxn proceeds, Q increases; at Equilibrium Q no longer changes

Formulas

marygracebunch2 — 2017-01-04 14:18:42 UTC

-The equilibrium expression is used to find the equilibrium constant, K (Kc or Kp), using the equilibrium concentrations (or pressures) of each gas in the equation.
-The second equation is used to convert between Kp and Kc

Common Confusions

marygracebunch2 — 2017-01-04 14:18:58 UTC

-GASES and SOLUTIONS are used in calculating Kc and Kp – solids and liquids are ignored b/c their concentrations are constant.
-Equilibrium is reached in a chemical reaction when the rates of forward and reverse reactions become equal
-The equilibrium constant is not the same as the rate of reaction- a large constant doesn't mean the rate will be fast.
-When K value is significantly smaller (less than 5%) than the initial concentration, we can generally ignore x

Practice Problems

marygracebunch2 — 2017-01-04 14:19:08 UTC

Multiple Choice and Free Response Included

Equilibrium Video 1

rprusia3881 — 2017-01-04 14:36:33 UTC

In this video Paul Andersen explains how equilibrium is achieved in a reversible reaction.

Quizlet

marygracebunch2 — 2017-01-04 14:44:16 UTC

Use this Quizlet to test your basic knowledge on Equilibrium! https://quizlet.com/_2yg0gn

Le Chatlier's Principle

marygracebunch2 — 2017-01-04 15:21:03 UTC

Increase in reactants or decrease in products = shift right
Decrease in reactants or increase in products = shift left

Change in Pressure:
Adding inert gas = no effect
Increase in pressure = shift to side with fewer gas molecules
Decrease in pressure = shift to side with more gas molecules

Change in Temp:

If exothermic: If Endothermic:

Increase temp = shift to left Decrease temp = shift to left
Decrease temp = shift to right Increase temp = shift to right

Interpreting K

marygracebunch2 — 2017-01-04 15:21:23 UTC

When K >> 1: concentrations of products are much greater than concentrations of reactants so the rxn is product favored.
When K << 1: concentrations of reactants are much greater than concentrations of products so the rxn is reactant favored.
When K ~ 1: reactants and products are present in significant concentrations at equilibrium

Comparing Q and K

marygracebunch2 — 2017-01-04 15:21:33 UTC

Allows us to determine the direction of a reaction

If Q < K, the reaction will shift to make more products
If Q > K, the reaction will shift to make more reactants
If Q = K, the reaction is at equilibrium

Manipulating equilibrium expressions

marygracebunch2 — 2017-01-04 15:21:52 UTC

Coefficient Rule: multiplying coefficients through by some factor n, K is raised to that same power
Reciprocal Rule: reverse a reaction, take inverse of k
Multiple Equilibria Rule: reactions are added together to form a net reaction, K is the product of each individual equilibrium

Practice Problem Answers

marygracebunch2 — 2017-01-05 15:37:36 UTC

Multiple Choice Problems (answer key)

Equilibrium Video 2

cberg21 — 2017-01-08 17:19:34 UTC

Another helpful Crash Course video

Equilibrium Visual

cberg21 — 2017-01-08 17:25:09 UTC

Steps to using an ICE Chart

marygracebunch2 — 2017-01-08 20:58:15 UTC

1. Determine balanced chemical equation
2. Determine direction of equilibrium
3. Fill in "I" on the ICE Chart with initial concentrations
4. Determine relative change (C)
5. Determine concentration at Equilibrium (E)
6. Solve for x by plugging into expression
7. Substitute x back in to calculate equilibrium concentration as a value
8. Check answers!

Multiple Choice Answer key

shawd420 — 2017-01-09 05:21:30 UTC

Video explanations and Copy of Key
https://youtu.be/W83NaZ_TJAc