Topic 10 Equilibrium

-Must be in a closed system -Forwards and backwards reaction are happening at the same time -Concentrations of the products and reactants remain constant

It favours the side with the fewest moles of gas

Equilibrium shifts away from the one increased

Equilibrium favours the endothermic reaction

The magnitude of Kc tells us the relative proportions of reactants and products in the equilibrium system

-A Kc value of 1 indicates that equilibrium is halfway between reactants and products -A Kc value >1 indicates that equilibrium is towards the products -A Kc value <1 indicates that equilibrium is towards the reactants

A homogenous equilibrium has everything present in the same phase

A heterogenous equilibrium has things present in more than one phase. The usual examples include reactions involving solids and gases, or solids and liquids.

La Chatelier’s principle states that a system at equilibrium moves in the direction that tends to minimise the disturbance. (Shifts in the direction that consumes energy).

The contact process is a method of producing concentrated sulphuric acid which is required for industrial use. ΔH=-96 kjmol^-1 -Exothermic -2 atm pressure.

-Step 1: Make sulfur dioxide S(g) + O2(g) –> 2SO2(g) -Step 2: Convert sulphur dioxide into sulfur trioxide (the reversible reaction at the heart of the reaction) 2SO2(g) + O2 ⇌ 2SO3(g) -Step 3: Convert sulfur trioxide into concentrated sulphuric acid H2SO4(l) + SO3(g) –> H2S2O7(l) H2S2O7(l) + H2O(l) –> 2H2SO4(l)

-Increasing the concentration of oxygen causes the position of equilibrium to shift towards the right -By increasing the proportion of oxygen you can increase the percentage of the sulfur dioxide converted.

-The forward reaction is exothermic, so increasing the temperature shifts the position of equilibrium to the left in the direction of the reactants. (Therefore, the higher the temperature, the lower the yeild of sulfur trioxide). -To get as much sulphur trioxide as possible in the equilibrium mixture, you need as low a temperature as possible -A compromise that allows a good speed of production and the right amount of sulfur trioxide is 400-450 degrees

-To get as much sulfur trioxide as possible, you need as high a pressure as possible (high pressures also increase the rate of reaction) -However at relatively low pressures there’s still a high conversion of sulfur dioxide into sulfur trioxide (99.5%), so increasing the pressure for a small improvement isn’t worth the expense.

-To shift equilibrium to right to increase yield of products. -Removal of products decreases rate of back reaction. -Time to reach equilibrium may be too long. -Unused reactants can be recycled.

N2 + 3H2 ⇌2NH3 -Forward reaction is exothermic. ΔH=-92 kjmol^-1 450°, 250 atm -Iron catalyst -Products are removed to increase effeciency.