Equilibrium

Equilibrium

The point in a reversible reaction where there is no change in the concentration of products and reactants (where rates of forward and reverse reaction are equal)

Le Chatelier’s Principle

For a system at dynamic equilibrium, if a change is made to the conditions, the position of the equilibrium will shift to counteract the change

Heat is a __ for exothermic reactions

Product

Heat is a ___ for endothermic reactions

Reactant

Heating an exothermic reaction shifts equilibrium

Left, towards the reactants

Cooling an exothermic reaction shifts equilibrium

Right, towards the products

Heating an endothermic reaction shifts equilibrium

Right, towards the products

Cooling an endothermic reaction shifts equilibrium

Left, towards the reactants

If pressure is increased (volume decreased)

Equilibrium shifts to the side with fewer gas molecules, because this reduces total pressure

If pressure is decreased (volume increased)

Equilibrium shifts to the side with more moles of gas, as this partially restores pressure

Adding a reactant

Shifts equilibrium right, towards products (to consume extra reactant)

Adding a product

Shifts equilibrium left, towards reactants (to consume extra products)

Diluting aqueous solutions

Shifts equilibrium to the side with greater number of aqueous particles

What is the only change that can be made to a system that changes Kc?

Temperature

Does catalyst addition impact equilibrium position

No - by lowering activation energy, it accelerates both forward and reverse reactions equally, allowing the system to reach equilibrium faster without changing Kc or the final concentrations of reactants and products

Open System

• Matter and Energy can enter or leave

• Reactants or products may escape

• Equilibrium cannot be maintained

• E.g. an uncovered beaker of water evaporating

Closed System

• Energy can enter or leave, but matter cannot

• All reactants and products remain inside

• Dynamic equilibrium can be established

• Eg. a sealed flask with NO2 gas

Physical Change

• No new substance is formed

• Usually reversible

• E.g. ice ← → water

Chemical Change

• New substances are produced

• Some are irreversible

• Some are reversible

• Irreversible, E.g. Burning wood

• Reversible, E.g. N2O4 (g) ← → 2NO2 (g)

Characteristics of series at equilibrium

• Forward reaction continues

• Reverse reaction continues

• Rates are equal

• Concentrations stay constant

• Colour, pressure and other observable properties remain constant

Endothermic reactions have ___ activation energy than exothermic reactions in equilibrium system

Greater