Topic 11 Equilibrium II

Write the units top and bottom to cancel. Invert the powers if there is more units under the line.

ICE method Initial moles Change in moles Equilibrium moles Use moles to calc concentration of reactants and products. Then put the concentrations into the KC equation. Then calc the units

Substitute values into the Kc equation. Rearrange to get the correct values alone. Square root to give final answer

The total pressure in a reaction is the sum of all the pressures of the individual gases (partial pressure) Example: SOCl2 <——> SO2 + Cl2 At equilibrium, the reaction vessel contains 263kPa of Cl2. The total pressure in the vessel is 714kPa. Calculate the partial pressure of SO2Cl2 We know the total pressure is the sum of all the partial pressures so Total pressure = pSO2Cl2 + pSO2 + pCl2 714 = pSO2Cl2 + pSO2 + 263 We know that Cl2 has a partial pressure of 263kPa. There is a 1:1 molar ratio with SO2. As this is a product too the partial pressure for SO2 is the same as Cl2. So let’s complete the equation further 714 = pSO2Cl2 + 263 + 263 714 - 526 = pSO2Cl2 188kPa

The partial pressure of gas is calculated using mole fractions. A mole fraction is the proportion of a gas in a gas mixture Mole fraction of a gas = Number of moles of gas / Total number of moles of gas in the mixture

Partial pressure = mole fraction of gas x total pressure in mixture Use the ICE table. Then calc mole fraction then x by total pressure

It is the equilibrium constant for an equilibrium reaction involving gases. We use partial pressures instead of concentrations. aA + bB <—–> cC + dD SMALLER LETTERS ARE POWERS Kp = (PC)(PD) / (PA)(PD)

Only includes gases

Temperature: Kp is only valid for one temperature Changing temperature will change equilibrium pressures, hence Kp will change too. If temp change causes equilibrium to shift right, Kp will increase If temp change causes equilibrium to shift left, Kp will decrease Pressure - The value of Kp is unaffected by any changes in Pressure Catalysts: Adding a catalyst has no effect on Kp A catalyst speeds up the forward and backward reaction equally A catalyst speeds up the rate at which equilibrium is established

Temperature: Temperature: Kc is only valid for one temperature Changing temperature will change equilibrium pressures, hence Kc will change too. If temp change causes equilibrium to shift right, Kc will increase If temp change causes equilibrium to shift left, Kc will decrease Concentration - The value of Kc is unaffected by any changes in concentration Catalysts: Adding a catalyst has no effect on Kc A catalyst speeds up the forward and backward reaction equally A catalyst speeds up the rate at which equilibrium is established