Equilibrium R2.3

Irreversible reactions

Reactions that only go to completion, they only go forward. Eg. explosions, decaying, burning

Reversible reactions

Reactions that can go forward and reverse them. Eg. ammonia production, hydration of certain things etc.

What is chemical equilibrium/dynamic equilibrium

Equilibrium is reached when the rate of the forwards and reverse reactions are equal and occuring at the same time.

The reactants and products’ concentration to remain constant over time. It is dynamic because both forward and reverse reactions are occurring simultaneously.

What happens when equilibrium is disturbed

It can be disturbed by changes in temp, pressure, or concentration of the components, the system acts to oppose the change and rebalance the system. It has to re-establish the equilibrium

Change in concentration

If you increase the reactants concentration, the forward reaction is favored to produce the least amount of concentration (particles)
If you increase product concentration, the reverse reaction is favored to produce the least amount of concentration (particles)

Increase of Pressure

Increase in P will favor the side of the reaction with the least number of moles of gasses).

For example, if N2 + 3H2 → 2NH3
There are 4 moles of gas in reactants and 2 in products.
If the pressure increases, the system will favor the reaction that produces the least amount of moles. In this case, the forward reaction will be favored.
If the pressure decreases, the system will favor the reaction that produces the most amount of moles. In this case, the reverse reaction is favored

Increase of temperature

In exothermic reactions, the heat is released meaning the delta H is a product. When temperature is added to the system, the reverse reaction is favored because it will cool down the system. Opposite goes for when the temperature in the system decreases.

The equilibrium law

Calculates constant K, products/reactants
Square brackets = concentration at equilibrium

What happens when K»1

Products/reactants, so there is a greater concentration of products than reactants.

Product is favored , so equilibrium lies on the right.

A lot of product is formed and a lot of reactant is consumed

What happens when K«1

Products/reactants, so there is a greater concentration of reactants than products

Reactant is favored, so equilibrium lies on the left

Not a lot of reactant consumed so not a lot of product formed

K=1

There is an equal concentration of products and reactants

No product/reactant is favored, equilibrium lies in the middle

What occurs to K when there is a change in the equation/coefficients

Effect of concentration on Kc

If you add more concentration (eg. to the products), the system will act to use up this product, so the reverse reaction will be favored to produce more reactants. Thus, there is an increase in both products and reactants (even though the system tries to use up all the product, it cannot use up all, and there is more reactant being produced in the process). Because both are increased, the equilibrium is not affected (Kc is not affected).

Effect of temperature on Kc