A5 Equilibrium Flashcards
Using Le Chatalier’s principle, explain the effect of increasing temperature.
Forwards reaction is exothermic or endothermic. So increasing temperature favours the forwards or backwards reaction. Equilibrium concentration of XXX increases.
Define dynamic equilibria.
Exists only in a closed system. The rate of the forward reaction is equal to the rate of the reverse reaction. The concentrations of reactants and products do not change.
Using Le Chatalier’s principle, explain the effect of increasing pressure.
Fewer gas moles on the left or right. Increasing pressure shifts equilibrium to the left or right hand side. Equilibrium concentration of XXX increases.
Using Le Chatalier’s principle, explain the effect of increasing concentration.
More reactant particles in mixture per unit volume. Equilibrium shifts to the right hand side.
Using Le Chatalier’s principle, explain the effect of a catalyst.
doesn’t change position of equilibrium
speeds up rate of forward and reverse reaction equally
will increase the rate at which an equilibrium is established
In equilibria industry, what are the advantages/disadvantages of temperature?
High temperature = quicker rate. High temperature is expensive.
In equilibria industry, what are the advantages/disadvantages of pressure?
High pressure = quicker rate. High pressure = expensive. High pressure = dangerous.
Why is it difficult to know the effect on equilibria if it is affected by both temperature and pressure?
Difficult to predict relative contributions of two opposing factors.
Why is nitrogen accessible in industry?
Occurs naturally in the air.
Explain the effect of changing temperature on the position of Kc.
If temperature change causes equilibria to shift to the right hand side, Kc value increases. If temperature change causes equilibria to shift to the left hand side, Kc value decreases. Kc value is not affected by pressure or catalysts.
Stages required for Kp with brief explanation of each one if applicable.
Initial moles. Change in moles (use molar ratio, and opposite sides of the equation are positive and negative). Equilibrium moles. Concentration (Conc=mol/vol).
What should always be ignored in Kc calculations?
Solids.
Stages for calculating Kp with a brief explanation of each one if applicable.
Initial moles. Change in moles (use molar ratio and opposite sides of equation have opposite signs). Equilibrium moles. Mole fraction (E moles over total moles). Partial pressure (multiply by volume).
What reactants and products should only be used in Kp calculations?
Gases only.
Explain the effect of increasing pressure (causing right hand shift) on the Kp equation.
Equilibrium shifts right, as right hand side has fewer moles. Increased pressure results in denominator of Kp expression increasing more than numerator. Numerator expression must increase to restore Kp.
Explain how increasing temperature affects the value of Kp.
If temperature change causes equilibria to shift to right hand side, Kp value increases. If temperature change causes equilibria to shift to left hand side, Kp value decreases. Kp value is not affected by pressure or catalysts.
features of dynamic equilibrium
rate of forward reaction= rate backwards reaction
conc dont change
closed system
closed system
is isolated from surroundings so temp, pressure and conc of reactants and products are unaffected by outside influences
increasing conc of of A and B
decreases conc of C and D
for a reaction to remain in equlbium
must be closed system
effect of conc - more reactant
shifts left
to reduce the effect of decreases in reactant
conc decrease
effect of conc if more products formed
position of equilbrium shifts to the right
increases conc
to reduce the effect of increase in conc of a reactant
change In temp
shifts to endothermic +ve side
decrease in temp
to exothermic -ve side
if forward exothermic
increase temp
- left and more reactants made
decreases temp
- right
more products made
if forward endo
increase temp
- right
more products made
decrease temp
- left
more reactants made
effect of pressure change
more gaseous molecules on one side
move moles
increase pressure
shifts to fewer moles
increase pressure
shifts to fewer moles
KC
Products/ reactants
conc
mol dm -3
pressure key words
position of equibrium shifts to right
reduces number of gaseous moles to minimise the increase in pressure
Kc units
mol dm -3
homogenous
contains equilbrium species that all have the same state
e.g. all gas
heterogenous
contains equblrium species that have different states
if equation for calculation Kc have mixed state symbols
ignore solid or liquid
so all gas in equation
Calculating Kc
ICE table
Kp
partial pressure
equibrium involving gases
mole fraction equation
number of moles A / total in gas mixture
sum of mole fraction in gas
equal 1
partial pressure equation
mole fraction A x total pressure
Kp
round brackets
equlburm shift in Kp
temp
forward endo
Kp increases
temp increases
increase yield of products
right
PP products Increases
PP reactant Decreases
eqiulbrum shift
catalyst Kp
unaffected
same as KC
temp effect on Kp if forward exo
Kp decreases with increase temp
decrease equilbrium yield of products
shifts left
Kc is small means
equilibrium to left
explain whether a catalytic converter acts as a homogenous or heterogeneous catalyst
heterogeneous
catalyss- solid - usually metal
reactants and products are gases
heterogenous
reactants and products have same state
Kp units
atm-1
