A5 equilibrium Flashcards
what are the two reversible reactions that come up a lot?
- dehydrating hydrated copper sulphate crystals.
- decomposition of ammonia chloride.
what is the equation and colour change for dehydrating hydrated copper sulphate crystals?
CuSO₄.5H₂O(s) >< CuSO₄(s) + 5H₂O(l)
blue > white
what is the equation for the decomposition of ammonia chloride?
NH₄Cl(s) >< NH₃(g) + HCl(g)
what is dynamic equilibrium?
the result of putting a reversible reaction into a sealed container.
what does the word dynamic refer to in dynamic equilibrium?
dynamic = forwards and backwards reactions are happening, but at same rate
what does the word equilibrium refer to in dynamic equilibrium?
concentrations of reactants and products remain constant
the amount of reactants and products at dynamic equilibrium is called the…
equilibrium position
position of equilibrium can shift further left or right if the conditions change:
- adding/removing one of the substances.
- changing the temperature.
- changing the pressure.
what is Le Chatelire’s principle?
EQUILIBRIUM SHIFTS (2nd to occur) to counteract CHANGE IMPOSED (1st to occur)
N₂O₄(g) >(endo)<(exo) 2NO₂(g)
what happens to the equilibrium if NO₂ is added?
- shifts to left.
- backwards reaction uses up extra NO₂(g).
N₂O₄(g) >(endo)<(exo) 2NO₂(g)
what happens to the equilibrium if the temperature is increased?
- shifts to right.
- forwards reaction is endothermic so absorbs extra heat.
N₂O₄(g) >(endo)<(exo) 2NO₂(g)
what happens to the equilibrium if the pressure is increased? (more gas = more pressure)
- shifts to left.
- fewer moles of gas on left, brings down pressure.
what is Kc?
the equilibrium constant
what is the equation for Kc?
Kc = [products] / [reactants]
balancing numbers = powers
[x] the concentration of x in mol dm-³
what do you ignore when working out Kc?
SOLIDS as their concentrations are constant
what is the only factor that affects Kc?
TEMPERATURE
PCl₅(g) >< PCl₃(g) + Cl₂(g)
ΔrH= +37kJ mol-¹
what affect would increasing the temperature have on Kc?
- equilibrium would shift to the right.
- forwards reaction is endothermic so absorbs extra heat.
> Kc increases.
PCl₅(g) >< PCl₃(g) + Cl₂(g)
ΔrH= +37kJ mol-¹
what affect does changing [] or pressure have on Kc?
- can shift the equilibrium.
> Kc remains constant.
what is Kp?
gas pressure
what is the equation of Kp?
Kp = p(products) / p(reactants)
what does Kp only include?
GAS
what does p stand for in the Kp equations?
the partial pressure of x, the proportion of the total pressure that is due to x alone.
for example:
in a box, 2 mol of N₂, 6 mol of H₂, 12 mol of NH₃
when working out pressure of N₂
if total pressure is 5 atm
p(N₂) = 2/20 x 5 atm
= 0.5 atm
N₂(g) + 3H₂(g) >< 2NH₃(g)
ΔH=-92kJ mol-¹
to maximise yield of NH₃ what should be done to temperature?
decrease temperature
- eqm shift to right as forward reaction is exothermic
= balance between yield & rate
// but not too much as rate would decrease
