topic 10: equilibrium I

occurs when forward and backward reactions are occurring at equal rates. the concentrations of reactants and products stays constant and the reaction is continuous

if an external condition is changed the equilibrium will shift to oppose the change (and try to reverse it)

if temperature is increased the equilibrium will shift to oppose this and move in the endothermic direction to try to reduce the temperature by absorbing heat

if temperature is decreased the equilibrium will shift to oppose this and move in the exothermic direction to try to increase the temperature by giving out heat

increasing pressure will cause the equilibrium to shift towards the side with fewer moles of gas to oppose the change and thereby reduce the pressure

Decreasing pressure will cause the equilibrium to shift towards the side with more moles of gas to oppose the change and thereby increase the pressure if the number of moles of gas is the same on both sides of the equation then changing pressure will have no effect on the position of equilibrium H2 + Cl2 —> 2HCl

I2 + 2OH- <—–> I- + IO- + H2O increasing the concentration OH ions causes the equilibrium to shift to oppose this and move in the forward direction to remove OH- ions. the position of equilibrium will shift towards the right, giving a higher yield of I- and IO-. ( the colour would change from brown to colourless) adding H+ ions reacts with the OH ions and reduces their concentration so the equilibrium shifts back to the left giving brown colour

a catalyst has no effect on the position of equilibrium, but it will speed up the rate at which the equilibrium is achieved it does not effect the position of equilibrium because it speeds up the rates of the forward and backward reactions by the same amount

T= 450oC, P= 200 – 1000 atm, catalyst = iron - low temp gives good yield but slow rate: compromise temp used - high pressure gives good yield and high rate: too high a pressure would lead to too high energy costs for pumps to produce the pressure

Stage 1: S(s) + O2(g) —> SO2(g) Stage 2: SO2 (g) + ½ O2 (g) <—> SO3 (g) H = -98 kJ mol-1 T= 450oC, P= 1 to 2 atm, catalyst = V2O5 - low temp gives good yield but slow rate: compromise moderate temp used - high pressure gives slightly better yield and high rate: too high a pressure would lead to too high energy costs for pumps to produce the pressure

CO(g) + 2H2(g) <—> CH3OH (g) H = -ve exo T= 400oC, P= 50 atm, catalyst = chromium and zinc oxides - low temp gives good yield but slow rate: compromise temp used - high pressure gives good yield and high rate: too high a pressure would lead to too high energy costs for pumps to produce the pressure

CH2=CH2(g) + H2O(g) <—> CH3CH2OH(l) H = -ve T= 300oC, P= 70 atm, catalyst = conc H3PO4 - low temp gives good yield but slow rate: compromise temp used - high pressure gives good yield and high rate: too high a pressure would lead to too high energy costs for pumps to produce the pressure - high pressure also leads to unwanted polymerisation of ethene to poly(ethene)

=[C]p[D]q/[A]m[B]n mA + nB <—> pC + qD

the greater the amount of products

Kc only changes with temperature it does not change if pressure or concentration is altered. a catalyst also has no effect on Kc