equil, Kc Flashcards
def: dynamic
the forward and backward reactions proceed at equal rates
def: equilibrium
the concentration of the reactants and products are constant
def: le chatelier’s principle
the position of equilibrium will shift to oppose change made to the system
how is dynamic equilibrium reached?
at the start of the reaction, forward reaction is fast and backward reaction is slow;
after start, backward reaction speeds up as the forward reaction slows;
the rate of the forward reaction becomes the same as the rate of the backward reaction.
what is the equilibrium position when there are more products than reactants?
equilibrium position is on the right
what is the equilibrium position when there are more reactants than products?
equilibrium position is on the left
pressure only affects reactions involving…
gases
(the more moles = the greater the pressure)
an increase in pressure will always move the equilibrium to the side with the ….. moles
fewest
a decrease in pressure will always move the equilibrium to the side with the … moles
most
if there is an equal number of moles, a change in pressure leads to ….
no effect
a decrease in volume of container , leads to an …. in pressure
increase
an increase in volume of container, leads to a …. in pressure
decrease
def: catalyst and how does it work
a substance that speeds up the rate of reaction without being used up;
provided an alternative reaction pathway with a lower activation energy
when a catalyst is added to a reversible reaction:
rate of both forward and backwards reaction increase equally by the same amount;
there is no change to the position of the equilibrium;
dynamic equilibrium is reached faster
an increase in temperature favours the …. direction
endothermic
a decrease in temperature favours the … direction
exothermic
when can dynamic equilibrium occur?
only occurs if the reversible reaction is carried out in a sealed container so no product can escape - closed system
what does a reversible arrow mean
a reversible reaction
if the concentration of a reactant is increased:
the equilibrium will shift to the right, to oppose the addition of [reactant],
so yield of [product] increases
if the concentration of a product is increased:
the equilibrium will shift to the left, to oppose the addition of [product]
so yield of [reactants] increase
if the concentration of a product is decreased:
the equilibrium will shift to the right,
to oppose the decrease in [products],
so yield of [product] increases
if the concentration of a reactant is decreased:
the equilibrium will shift to the left,
to oppose the decrease in [reactants],
so yield of [reactant] increases
exothermic reactions
releases heat energy,
temperature of surroundings increase,
enthalpy change is negative (minus delta H)
endothermic reactions
absorb heat energy,
temperature of surroundings decrease,
enthalpy change is positive (plus delta H)
why are catalysts added to reversible reactions?
to reduce the time taken to reach dynamic equilibrium
def: compromise conditions
choosing conditions which produce maximum yield of product,
in shortest amount of time,
for least cost
why are compromise conditions neccessary?
higher pressure would be too expensive
450 degrees C gives a good yield in a fast time
catalyst doesn’t affect position of equilibrium, but reduces cost of reaction as less fossil fuel burned to generate heat energy
Kc
[products] over [reactants]
[ ] = concentration (moldm-3)
c means concentration
molar ratio = [ ] times to power of ?
ICEE
If Kc / Kp is exactly 1:
conc of products is equal to conc of reactants,
equillibirum is in middle
If Kc / Kp is greater than 1:
more products than reactants at equilibrium,
equillibirum shifted to the right
If Kc / Kp less than 1
more reactants than products at equilibrium,
equillibirum shifted to the left
def: homogenious reaction
system where all the reactants and products are in the same phase
Kp
(pp products) over (pp reactants)
p means pressure (kPa)
gas phase equilibria reactions
ICEMP
what is a partial pressure?
the contribution one gas makes,
also the sample of gas it could create if in a container on its own
equation of partial pressure of A:
mole fraction of A x total pressure
equation for mole fraction of A
no. of moles of A in equil mixture / total no. of moles of all gases at equil
(all molar fractions within a mixture should always add up to 1)
which condition only can affect Kp of Kc value?
temperature
what happens to the value of Kp if temperature increases?
value of Kp decreases
what happens to the value of Kp if temperature decreases?
value of Kp increases
