Chemical Equilibrium (Pt. 4)

The Properties of the Equilibrium Constant K

plus ExamplesBy Shawn P. Shields, Ph.D.

This work is licensed by Dr. Shawn P. Shields under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.

Recall: The Law of Mass Action

Consider the generalized reaction

Reactants A and B

Products C and D

coefficients

Recall: The Law of Mass Action

For the reaction

The relationship between the value of the equilibrium constant K and the concentrations of reactants and products is

𝐩𝐫𝐨𝐝𝐮𝐜𝐭𝐬𝐫𝐞𝐚𝐜𝐭𝐚𝐧𝐭𝐬

Property 1: Reversing the Reaction and the Value of K

For the reaction

Reverse the reaction:

or or K-1

Property 1: Reversing the Reaction and the Value of K

If we reverse a reaction, the new K for the reversed reaction is the inverse of the original value.

or K-1

Property 2: Adding Two Reactions and the Equilibrium Constant

If we add two or more reactions together to get a new reaction, multiply the equilibrium constants together.

Reaction 1: Reaction 2:

K1K2

Property 2: Adding Two Reactions and the Equilibrium Constant

If we add two or more reactions together to get a new reaction, multiply the equilibrium constants together.Reaction 1: Reaction 2:

The new equilibrium constant K3 = K1 K2

K1K2K3

Property 3: Multiplying Coefficients by a Factor and the Equilibrium Constant

If we multiply the coefficients in a reaction by a factor, the new equilibrium constant K is the original value raised to the power equal to that factor.

Original rxn:

Mult by factor of 4: K

K4

Property 3: Multiplying Coefficients by a Factor and the Equilibrium Constant

We do the same thing if the factor is a fraction… the new equilibrium constant K is still the original value raised to the power equal to that factor.

Original rxn:

Divide coeff by 4:

K

Example 1: Reversing the Reaction and the Value of K

For the reaction below at a certain temperature,

What is the value for K for the reaction below?

Example 1 Solution

Original Reaction:

What is the value for K for the reaction or K-1

Example 2: Adding Two Reactions and the Equilibrium Constant

Add the two reactions below to get a new reaction. Determine the value for the equilibrium constant for the new reaction.Reaction 1: Reaction 2:

K1= 5.1K2 = 0.15

Example 2 Solution

Add the two reactions below to get a new reaction. Determine the value for the equilibrium constant for the new reaction.Reaction 1: Reaction 2: 2

K1= 5.11K2 = 0.150

K3 = K1 K2 = 5.11 0.150 = 0.767

Example 3: Multiplying Coefficients by a Factor and the Equilibrium Constant

For the reaction below at a certain temperature,

What is the value for K for the reaction below?

Example 3: Multiplying Coefficients by a Factor and the Equilibrium Constant

The coefficients were multiplied by

Next up, ICE Tables and Equilibrium

Calculations (Pt 5)