Chemical equilibrium Flashcards
describe DYNAMIC equilibrium
- forward and reverse reactions proceed at the same rate
- concentration of reactants and products remain CONSTANT
- closed system
what’s Le Chatelier’s principle
states that if a system at equilibrium is disturbed, the position of equilibrium moves in the direction to minimise the change
effect of increasing conc on equilibrium
shifts in opposite direction to remove the reagent.
effect of decreasing conc on equilibrium
shifts in the same direction to replace what has been lost
what could cause a decrease in concentration of a species at equilibrium
- Evaporation
- Addition of water
- Neutralisation
how does evaporation decrease concentration of a species at equilibrium
- Open system
- Gas removed
- [gas] decreases
how does addition of water decrease concentration of a species at equilibrium
- Aqueous species diluted
- [aq] decreases
how does neutralisation decrease concentration of a species at equilibrium
- H+ ions added to a base, forming water
- [base] decreases
- OH-/base added to an acid, forming water
- [acid] decreases
effect of increasing temperature on equilibrium
position of equilibrium shifts in endothermic direction.
effect of decreasing temperature on equilibrium
position of equilibrium shifts in exothermic direction.
effect of increasing pressure on equilibrium
shifts in direction with the fewest number of moles of gas
effect of decreasing pressure on equilibrium
shifts in direction with the greatest number of moles of gas.
why are compromise conditions used in industry
- to ensure a reasonably high yield of product at a high rate
- for example if forward reaction is exothermic then temp can’t be too high as this would favour the reverse reaction
disadvantages of using high temp
- increases energy costs
- Reduces yield of exothermic reactions
advantages of using high temp
- Increases rate of reaction
- Increases yield of endothermic reactions
advantages of using low temp
- Increases yield of exothermic reactions
- Reduces energy costs
disadvantages of using low temp
- Decreases yield of endothermic reactions
- Decreases rate of reaction
advantages of high pressure
- Increases yield of forward reaction produces fewer moles of gas
- Increases rate of reaction
disadvantages of high pressure
- Decreases yield if forward reaction produces more moles of gas
- Safety risk / uses lots of energy / expensive
advantages of low pressure
- Increases yield if forward reaction produces more moles of gas
- Safer / cheaper / uses less energy
disadvantages of low pressure
- Decreases yield if forward reaction produces fewer moles of gas
- Decreases rate of reaction
advantages of catalysts
- Increases rate of reaction
- Lower temperatures can be used, lowers cost
disadvantages of catalysts
- No effect on yield
- Can be expensive (limited resources)
Kc expression for aA + bB ⇌ cC + dD
Kc = [C]c [D]d / [A]a [B]b
Kc = [products] / [reactants]
Kc is constant at constant….
temperature
If [product] expression is > [reactant] expression…
- Equilibrium position lies to the right.
- Forward reaction favoured.
- Kc > 1
If [product] expression < [reactant] expression…
- Equilibrium position lies to the left.
- Reverse reaction favoured.
- Kc < 1
what happens when the conc of a product doubles (numerator)
- Kc will double with it.
- Kc will restore itself by doubling the denominator ([reactants]).
how do you calculate equilibrium moles
- ICE
Initial moles
Change in moles
Equilibrium moles
