2.10 Equilibrium

Reversible reaction

A reversible reaction is a reaction which can go in both the forward and backward directions.

E.g changes in state ice

What is closed system

no substances and no energy exchanged with the surroundings.

Nitrogen + hydrogen equilibrium ammonia formula

N2(g) + 3H2(g) |=| 2NH3(g)

Dynamic equilibrium

in a dynamic equilibrium the amounts of each reactant and product remain constant and the rate of the forward reaction is equal to the rate of the reverse reaction

Homogeneous reaction

a reaction in which the reactants and products are in the same physical state.

CATALYST MUST BE SAME STATE TOO

Heterogenous reaction

reaction in which the reactants and products are in a different physical state.

Position of equilibrium on products

• equilibrium left, little product is formed.

•  equilibrium right, lots of product has formed.

Equation for equilibrium constant and units

Kc = [Products] over [reactants]

moldm-3

High Kc value indicates

> 1 position of equilibrium lies to the right-hand side.

<1 position of equilibrium lies to left

Le chateliers principle

if a change is made to the conditions of a system at equilibrium, then the position of the eguilibrium moves to oppose that change in conditions.

Adding catalyst to equilibrium

Does not impact position fo equilibrium as it speeds up rate of forward and reverse reactions equally

Increase Concentration of reactant on equilibrium

Reactant Forward reaction - faster (more particles more collision, more successful collisions) -

Equilibrium moved to right

Changing pressure

Increase pressure- equilibrium shifts to reduce it by moving to side with least number of gas molecules lower pressure

Changing temperature on equilibrium rules

Increase temp = favours endothermic

Decrease temp= favours Exothermic

Haber process formula

N2 (g) + 3H2 (g) {} 2NH3 (g) Delta H = -92kjmol-1 Exothermic

Temperature in haber process

Decrease temp - move position of equilibrium to right, to increase temp, gives high yield of ammonia

Why not use low temp in haber process

Low temp give very slow reaction so compromise temp of 450oC used give reasonable rate and yield

Pressure haber process

High pressure- equilibrium shifts right to decrease pressure (fewer gas molecules) , good yield of a,,o is

Why not very high pressure

Large amount of energy needed to compress gad and thick pipes required expensive, so compromise pressure of 200atm

Conditions for haber process

Temp : 450oC

Pressure: 200atm

Iron catalyst

Costs reduced in haber process

Recycling unused nitrogen and hydrogen.

Using the energy given off in the reaction to heat up the incoming gases

Contact process formula

Sulphuric acid produced

2SO2 (g) + O2(g) |=| 2SO3 (g) delta H -197

Temp on contact process

Increase temp - equilibrium right favour endothermic reaction - lower yield of product , compromise temp 450oC

Pressure on contact process

Increase pressure- equilibrium move right - fewer gas moles higher yield - compromise pressure of 2atm

Catalyst in contact process

vanadium (V) oxide as a heterogeneous catalvst allows equilibrium to be reached more quickly.

Conditions contact process

Temperature: 450°C

Pressure: 2 atm

Vanadium(V) oxide (V2O5) catalyst