6. Equilibrium

Question 1

the equilibrium law states

and the equilibrium constant is

Answer 1

for equilibrium aA +bB cC + dD
Kc= [C]c [D]d / [A]a [B]b
Kc= [products] / reactants

Question 2

a homoogeneous equilibrium is

Answer 2

an equilibrium in which all the species making up the reactants and products are in the same physical state

Question 3

a hetrogeneous equilibrium is

Answer 3

an equilibrium in which species making up the reactants and products are in different physical states

Question 4

an equilibrium is when

Answer 4

the rate of the forward and reverse reaction are equal

Question 5

Kc remains constant once an equilibrium is established unless

Answer 5

the temperature of reaction changes
e.g
A + B C + S △H=-100kJmol-1 (forward reaction exothermic, give out heat. reverse reaction endothermic, take in heat)
temperature increase reverse endothemic reaction favoured. reactants increase Kc decreases
temperature decrease forward exothermic reaction favoured. products increase Kc increase

Question 6

units of kc

Answer 6

e.g [A]2 / [B]
(moldm-3)2 / moldm-3 = moldm-3
(only one moldm-3 left on top others cancel out)

Question 7

determining concentrations at equilibrium

titration and drawbacks

Answer 7

titrating one of the reactants/products against substance with known concentration enables us to find out how much of reactant/product present
amount of substances must be carefuly determined
drawbacks
reactant/product has to be removed from reaction mixture- alters position of equilibrium.
other substances might be present that can affect results of titration

Question 8

determining concentration at equilibrium

colorimeter

Answer 8

can monitor the concentration of reactant/product throughout.
(coloured substances alter amount of light that can pass through. more intense colour = higher conc substance absorbs more light)

Question 9

mole conc volume triangle

Answer 9

mol

conc | volume (in dm3)

Question 10

Kc for hetrogeneous equilibria

Answer 10

molar concentrations for solids and liquids do not change because their volume remains constant
for Kc
conc of solid substance not included in expression
conc of pure liquid not included in expression

Question 11

Kc large number means

Answer 11

higher conc of products than reactants

equilibrium to the right

Question 12

Kc low number means

Answer 12

higher conc of reactants than products

equilibrium to the left