Topic A5 - Equilibria
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What is Le Chatelier’s Principle?
equilibrium shifts to counteract change imposed
What are the conditions that change that cause equilibrium to shift?
-adding/ removing one of the substances (change in reactant and product concentration) -changing the temperature -changing the pressure
Which way does the equilibrium shift if temperature increases?
shifts in direction of endothermic reaction (i.e. if forwards reaction is endothermic, equilibrium would shift right)
Which direction does equilibrium shift if you add more reactants?
shifts to the right - as the forwards reaction uses up extra reactants
What happens to the position of equilibrium if pressure increases?
equilibrium shifts to side with fewer moles of gas, as this brings down the pressure (i.e. fewer moles of gas on left, equilibrium shifts left)
What is the only condition that affects Kc?
temperature
What happens to Kc when temperature increases (forwards reaction = endothermic)?
-equilibrium shifts in direction of endothermic reaction (shifts RIGHT) -as endothermic reaction absorbs extra heat Therefore, Kc increases
What affect does changing concentrations and pressure have on Kc value?
no affect - Kc remains constant
What 2 conditions are required for a system to be in ‘dynamic equilibrium’?
• rate of forward reaction = rate of backward reaction • concentration of reactants and products do not change`
For a system to remain in equilibrium, the system must be…
closed - isolated from surroundings, temperature, pressure and concentrations of reactants and products are unaffected by outside influences
What is homogenous equilibrium?
contains equilibrium species that all have the same state or phase (e.g. all species are gases)
What states does Kc only include?
gas aqueous
What is a heterogenous equilibrium?
contains equilibrium species that have different states or phases
What is meant by the partial pressure of a gas?
the contribution that the gas makes towards the total pressure partial pressure = mole fraction x total pressure (sum of partial pressures = total pressure)
What are suitable units for Kp?
kPa, Pa, atm
Why do pressure and concentration changes not change Kc value?
• causes a change in position of equilibrium • ratio of reactants:products at equilibrium remains the same • as Kc is the ratio of the concentrations of products to reactants at equilibrium, Kc value does not change