3.2.3 Chemical Equilibrium Flashcards Preview

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Flashcards in 3.2.3 Chemical Equilibrium Deck (15)
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1

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

2

Le Chatelier's Principle

equilibrium shifts to oppose any changes to the system's conditions (only for homogeneous equilibria)

3

Homogeneous Equilibria

all products and reactants in the same phase

4

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.

5

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)

6

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

7

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

8

Le Chatelier's Principle making ethanol

ethene(g) + H2O(g)< -> ethanol (g) (-46kjmol-1)
pressure= 60 atm
temp= 300 C
catalyst= phosphoric acid

9

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)

10

Kc

Equilibrium Constant

11

Kc calculation

product conc/ reactants conc

12

Interpreting Kc values

if Kc > 1 = equilibrium shifted more to products
Kc < 1 = equilibrium shifted more to reactants

13

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

14

Investigating Equilibrium- changing conc

Fe3+(aq) + 3SCN+(aq) Fe(SCN)3 (aq)
yellow colourless blood red

15

Investigating Equilibrium- changing temp

2NO2 (g) N2O4 (g) (forwards exo, backwards endo)
brown colourless
(place in warm and cool water baths)