TOPIC 10: Equilibria 1

Question 1

Reversible reactions

Answer 1

Forward
- initially reactants used up quickly then slow as their concentration drops
Backward
- initially reactants are reformed slowly then speed as concentration of products increase
Dynamic equilibrium
Rates are equal so concentration remains constant (graph plateaus)
CLOSED SYSTEM

Question 2

Le Chatelier’s principle

Answer 2

If a reaction at equilibrium is subjected to a change in pressure, temperature or concentration, the position of equilibrium will move to counteract the change.

(Homogeneous equilibria, all same state)

Question 3

Increase concentration of reactant or product, equilibrium will…

Answer 3

Shift, to reduce the concentration, to the right or left so more products or reactants are formed

Question 4

Increase pressure, equilibrium will…

Answer 4

Shift, to reduce the pressure, to the side with the fewest number of gas particles (moles)

Question 5

Increase temperature, equilibrium will…

Answer 5

Shift, to reduce the temperature, in the endothermic direction (H+ve)

Question 6

Catalysts

Answer 6

No effect on position of equilibrium

Speed up rate equally so rate at which equilibrium reached

No effect on yield

Question 7

Making ethanol:

C2H4 + H2O -><- C2H5OH
H : -ve

Answer 7

Pressure: 60 atm high to increase rate and yield but cost compromise
Temperature: 300C compromise between yield and rate

Exothermic and fewer moles

Question 8

Kc The equilibrium constant

Answer 8

(homogeneous, all same state)
Molar values in front of species are powers in expression

([X]^a x [Z]^b)/([Y]^c x [R]^d

(if heterogeneous, different states)
not include solids and pure liquids

Question 9

Effect in Kc value

Answer 9

Temperature: changing, if shift to right increase Kc

Concentration: unaffected

Catalyst: non