Chem 1210 Unit 1

what is chemical equilibrium?

a state in a reversible chemical reaction where the forward and reverse reaction rates are equal

• no net change in the concentrations of reactants and product

when does a reaction reach equilibrium?

Depends on the equilibrium constant (K)

How long does it take to reach equilibrium?

Depends on the reaction rates

on a concentration time graph of a reactant and product, when is equilibrium reached?

equilibrium is reached when both reactant and product concentrations are stable, and do not change.

on a rate and time graph, when is equilibrium reached?

equilibrium is reached when both reactant and product rates merge to become the same value.

In chemistry, what does the equilibrium quotient Q mean?

Q is the ratio of product concentrations to reactant concentrations at any point during a reaction.

what does a q value help us determine when compared to K values?

It helps determine the direction a reaction will proceed to reach equilibrium

If Q is larger than K, which way will a reaction proceed in order to reach equilibrium?

Proceeds to the left

If Q is smaller than K, which way will a reaction proceed in order to reach equilibrium?

proceeds to the right

What does the equilibrium expression K mean?

The equilibrium constant K represents the ratio of product concentrations to reactant concentrations at equilibrium in a chemical reaction

• It indicates the extent of the reaction at equilibrium

• it will determine when a reaction will reach equilibrium

What are the 2 different types of equilibrium constant K values

Kc and Kp

Kc

relates different concentrations

Kp

relates partial pressures instead of []

• can be mixed and matched to have some be [] and some be partial pressures

Can relate Kp to Kc through the ideal gas law

K p=K c×(RT)Δn

What type of values (I.C.E) do we use in the K value?

only equilibrium values

When trying to solve for a third K value when given 2 k values, what 2 different methods can you use to solve for K3?

1. The property that the K equation 1 x K equation 2

2. make a net K equations by cancelling out the 2 givens

How can K tell us the composition of an equilibrium mixture (more reactants or products)

we can use K to tell us if there are more products or more reactants

• Q is used to tell us the direction of a reaction to establish an equilibrium

• the magnitude of K tells us what the equilibrium mixture itself is like

A small K (K<10-3) means the equilibrium mixture is mostly

reactants

A large k (k>103) means the equilibrium mixture is mostly

products

an intermediate K value (10-3<K<103) means the equilibrium mixture is

mostly equal

What are 3 ways to use K?

1. use K to determine the equilibrium mixture

2. to predict the direction of reaction

3. predict the equilibrium system’s response to stress

what is the le chatelier principle

Le Chatelier's Principle: It states that if a system at equilibrium is disturbed, the system will shift to counteract the disturbance and restore equilibrium.

what are some LCP changes

1. adding or removing substances

2. changing temp

3. changing pressure or volume

4. adding a catalyst or inert gas

what effect does adding a catayst have

will lower the Ea for the reverse and forward rxn

what effect will an inert gas have on Kc or Kp value

will not change K