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Flashcards in chemical equilibrium Deck (83)
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1

chemical equilibrium

a state of dynamic balance where rate of forward reaction equals rate of the reverse reaction

2

Le Chatelier's Principle

-if a stress is applied to a system at equilibrium
-system readjusts to oppose stress applied

3

Le Chatelier's Principle and gases

Le Châtelier's Principle predicts that in an all-gaseous reaction, an increase in pressure will favour the reaction which takes place with a reduction in volume

4

Equilibrium constant

formula in hardback

5

Kc

[ ] means concentration in moles per litre

-if greater than 1, products are favoured. The larger the value of Kc, the greater is the extent to which equilibrium is pushed towards products
-if less than 1, reactants are favoured. Low value of Kc - only small fraction of reactants converted to products

6

Le Chatelier and industry

ammonia and haber process
sulfuric acid and contact process

7

ammonia and haber process

predict max yield at high pressure / low temperature

reality = 200 atm and 500°C

8

sulfuric acid and contact process

predict max yield at high pressure / low temperature

reality = one atm and 450°C

9

large Kc

equilibrium far to right

lots of product produced

10

Small Kc

equilibrium far to left

v little product formed

11

2Mg + O₂ --> 2MgO

-2 Mg atoms react with one O₂ molecule to form 2 molecules of magnesium oxide
-v hard to turn MgO back to magnesium and oxygen
-reaction "goes to completion"

12

N₂ + 3H₂ --> 2NH₃

-not all reactions go to completion
-some reactions are 'reversible'
-some of ammonia formed decomposes and becomes nitrogen and hydrogen again
-reaction takes place both in forward and backward reactions

13

chemical equilibrium

a balance where the rate of the forward reaction is equal to the rate of the backwards reaction

14

dynamic equilibrium

equilibrium is constantly 'moving'

15

stress

stress is a change in reaction conditions
-concentration of reactants/products
-temperature
-pressure
-catalyst

if we change conditions of reaction at equilibrium, reaction readjusts itself to relieve stress

16

pressure

-if there are same no. of molecules on both sides of reaction, change in pressure will have no effect on equilibrium
-pressure only has effect on gaseous reactions

17

temperature

-forward reaction is exothermic ~(produced heat)
-when temp of reaction is changed, reaction shifts itself to relieve stress

18

concentration

-changing conc of one of the reactants shifts reaction to right (forwards) to relieve stress
-changing conc of product shifts reaction to left (backwards) to relieve stress

19

stresses that can be applied

pressure increased/decreased
temperature increased/decreased
concentration of 'x' increased/decreased

20

system's response - pressure increased

equilibrium shifts to the side with the lower total number of molecules

21

system's response - pressure decreased

equilibrium shifts to the side with the higher total number of molecules

22

system's response - temperature increased

endothermic reaction is favoured

23

system's response - temperature decreased

exothermic reaction is favoured

24

system's response - concentration of 'X' is increased

reaction that removes 'X' is favoured

25

system's response - concentration of 'X' is decreased

reaction that forms 'X' is favoured

26

haber process

N₂ + 3H₂ 2NH₃
-iron catalyst
-forward reaction is exothermic
-made at IFI plant in Cobh, Cork

27

haber process - pressure

-4 molecules on left, 2 on right
-increase pressure will favour production of ammonia
-keeping pressure high is expensive
-200 atmospheres - most cost effective + safe

28

haber process - temperature

-forward reaction in exothermic
-lowering temp will favour production of ammonia
-too slow at v low temps
-500°C temperature

29

N₂ + 3H₂ 2NH₃
chemical equilibrium

-at beginning, conc of ammonia is 0
-as reaction proceeds, conc of N₂ + H₂ decreases, conc of NH₃ increases
-when rate of production of NH₃ equals its rate of decomposition, reaction has reached equilibrium

30

stoichiometry - empirical formula

gives the simplest whole number ratio of the numbers of the different atoms present in the molecule