1.6 Equilibria

Question 1

what does the term dynamic mean?

Answer 1

• both forward and backward reactions are occurring simultaneously

Question 2

give two features of dynamic equilibrium

Answer 2

• forward and backward reactions occuring at equal rates
• the concentration of reactants and products stay constant

Question 3

what does le chateliers principle state?

Answer 3

• it an external condition is changed the equilbrium will shift to oppose the change

Question 4

what happens if the temperature is increased?

Answer 4

• the equilbrium will shift to oppose this and move in the endothermic direction to try to reduce the temperature by absorbing heat

Question 5

what happens if the temperature is decreased?

Answer 5

• the equilibrium will shift to oppose this and move in the exothermic direction to increase the temperature by giving out heat

Question 6

exam question : what will happen to the yield of ammonia if the temperature is increased

N2 + 3H2 >< 2NH3 delta H = -ve

Answer 6

• if the temperature is increased equilbrium will shift to the endothermic side, backwards as forward reaction is exothermic to dry and decrease the temp
• yield of ammonia becomes lower

Question 7

what happens to the equilibrium if you increase the pressure

Answer 7

• increasing pressure will cause equilbrium to shift to side with fewer moles of gas
• to oppose the change and thereby reduce the pressure

Question 8

what happens to the equilbrium if you decrease the pressure?

Answer 8

• decereasing pressure will cause equilbrium to shift towards the side with more moles of gas
• to oppose the change and thereby increase the pressure

Question 9

what happens if the number of moles of gas is the same on both sides?

Answer 9

• changing pressure will have no effect on position of equilbrium

Question 10

why does pressure tend to get increased?

Answer 10

• can give a higher yield of product
• produce a faster rate

Question 11

what happpens if you increase the concentration of a substance?

Answer 11

• equilibrium will shift to opposie this change and move towards the side not containing the substance
• so colour can change

Question 12

what effect does a catalyst have on the equilbrium

Answer 12

• no effect on position of equilibrium
• speeds up the rate at which equilibrium is reached

Question 13

why is a low temp and high pressure used in Haber process?

N2 + 3H2 > 2NH3 - ve

Answer 13

• low temp gives a good yield but slow rate, so a compromise temp is used
• high pressure gives good yield and high rate, too high pressure is expensive

Question 14

why are catalysts used economically?

Answer 14

• they speed up rate, allowing a lower temp to be used, so lower energy costs

Question 15

what does the term carbon neutral mean?

Answer 15

• an activity that has no net annual carbon emissions to the atmopshere

Question 16

what is the general equation for Kc?

mA + nB > pC + qD

Answer 16

Kc = [C]^p [D]^q / [A]^m [B]^n

Question 17

how do units work in Kc?

Answer 17

• replace each conc with moldm^-3
• cancel out units when required and find overall unit

Question 18

how can Kc change?

Answer 18

• ONLY WITH TEMPERATURE

Question 19

if Kc is small what do we say?

Answer 19

• the equilibrium favours the reactants