3.2.3 Chemical Equilibrium Flashcards
Conditions for Dynamic Equilibrium
- Closed system
- rate of forwards reaction is equal to the rate of reverse reaction
- concentrations of forwards and reverse reactions stay constant over time (don’t change
Le Chatelier’s Principle
equilibrium shifts to oppose any changes to the system’s conditions (only for homogeneous equilibria)
Homogeneous Equilibria
all products and reactants in the same phase
Le Chatelier’s and Concentration
increase concentration of reactants, equilibrium shifts to right to oppose the change, more products made
increase concentration of products, equilibrium moves left to oppose change, more reactants made.
Le Chatelier’s and Pressure
increasing the pressure will cause equilibrium to move to the side with less gaseous molecules to reduce pressure (vice-versa)
Le Chatelier’s and Temperature
increase the temp the equilibrium moves favour more endothermic reaction
decrease the temp. the equilibrium moves to favour more exothermic reaction
Le Chatelier’s and a Catalyst
a catalyst doesn’t affect equilibrium position, it speeds up the rate of reaction for both forward and reverse reaction equally.
speeds up rate at which equilibrium is reached
Le Chatelier’s Principle making ethanol
ethene(g) + H2O(g)< -> ethanol (g) (-46kjmol-1)
pressure= 60 atm
temp= 300 C
catalyst= phosphoric acid
Making Ethanol Compromises
low temps would mean a higher yield of ethanol but low temps mean a slower rate of reaction (300C is a compromise between yield and rate)
high pressures would mean a higher rate and higher yield, high pressures need expensive, thick vessels and are dangerous. (compromise between yield/rate and cost)
Kc
Equilibrium Constant
Kc calculation
product conc/ reactants conc
Interpreting Kc values
if Kc > 1 = equilibrium shifted more to products
Kc < 1 = equilibrium shifted more to reactants
Changing Kc values
Only temperature can affect Kc values
temp change causes eq to more right = Kc increases
temp change causes eq to move left = Kc decreases
Investigating Equilibrium- changing conc
Fe3+(aq) + 3SCN+(aq) Fe(SCN)3 (aq)
yellow colourless blood red
Investigating Equilibrium- changing temp
2NO2 (g) N2O4 (g) (forwards exo, backwards endo)
brown colourless
(place in warm and cool water baths)
