dynamic equilibrium

Question 1

what is dynamic equilibrium

Answer 1

• when a reversible reaction is left in a sealed container, the forwards and backwards reactions will eventually ‘balance out’
• from that point onwards, the mixture of reactants and products in the container is referred to as being in dynamic equilibrium:
  -> dynamic: the forwards and backwards reactions are still happening, just at the the same rate
  -> equilibrium: the concentrations of reactants and products remain unchanged

Question 2

eg. for the decomposition of N2O4

Answer 2

• if you leave N2O4 in a box, some of it breaks apart forming (2)NO2
• but then the NO2 that was just made could recombine to form N2O4 again
• after a while, the breaking apart and recombining end up happening at the same rate
• so the overall concentrations of N2O4 and NO2 end up staying the same
• same argument applies if you start will all NO2 instead of N2O4, or even a mixture of both

Question 3

what is the equilibrium position

Answer 3

the resulting balance of products and reactants in an equilibrium mixture

Question 4

what is it called when there are more products than reactants in the mixture

Answer 4

called ‘on the right’ because the products are on the right hand side of the equation

Question 5

what is it called when there are more reactants than products in the mixture

Answer 5

‘on the left’ because the reactants are on the left hand side of the equation

Question 6

how can you tell where an equilibrium is

Answer 6

by observing or measuring one of the substances

Question 7

what variables can cause the position of an equilibrium to be shifted

Answer 7

• amounts of reactants or products
• gas pressure
• temperature

Question 8

what does Le Chaterlier’s Principle state

Answer 8

the equilibrium shifts to counteract any change imposed on it

Question 9

which direction does th equilibrium shift when a substance is added

Answer 9

in whichever direction uses it up

Question 10

which direction does th equilibrium shift when a substance is removed

Answer 10

whichever direction creates it

Question 11

which direction does th equilibrium shift when gas pressure is increased

Answer 11

to whichever side has fewest moles of gas

Question 12

which direction does th equilibrium shift when gas pressure is decreased

Answer 12

whichever side has most moles of gas

Question 13

which direction does th equilibrium shift when temperature is increased

Answer 13

in whichever direction is endothermic

Question 14

which direction does th equilibrium shift when temperature is decreased

Answer 14

in whichever direction is exothermic

Question 15

what is the easiest way to change the concentration of a substance

Answer 15

to add or remove some of it from the mixture:
- if you add something, the equilibrium will shift to remove the extra you just added
- if you remove something, the equilibrium will shift to create more of it

Question 16

gas pressure changes:

Answer 16

gases exert pressure on the sides of the container, and more gas means higher pressure
- if you increase gas pressure, the equilibrium will shift to lower it down
- if you decrease gas pressure, the equilibrium will shift to bring it back up

Question 17

in what situations does a change in gas pressure have no effect

Answer 17

when there are no moles of gas on either side or the are equal moles of gas on both sides

Question 18

how does the equilibrium affect temperature

Answer 18

by absorbing or releasing heat energy:
- if you increase temperature, the equilibrium will shift to cool it back down
- if you decrease temperature, the equilibrium will shift to heat it back up

enthalpy change tells you whether the forwards reaction is endothermic (+) or exothermic (-)
-> backwards reaction is opposite of forwards reaction

Question 19

catalysts:

Answer 19

• catalysts increase the rates of both forwards and backwards reactions, they balance
• that means adding a catalyst has no effect on the position of an equilibrium