ES 4

Question 1

what are the characteristics of dynamic equilibrium

Answer 1

-established in a closed system where nothing is added or taken away
-the rate of forward reaction is the same as the rate of reverse reaction
concentrations of reactants and products remain the constant

Question 2

what happens inside a dynamic equilibrium of bromine

Answer 2

-molecules of bromine gas and liquid are constantly moving and colliding
-gas molecules collide with the molecule on the surface of the liquid so enter liquid phase
-near the surface of the liquid some molecules escape into the gaseous phase
-reversible reaction occurs

Question 3

what is Le Chatelier’s principle

Answer 3

when a system in dynamic equilibrium is subject to change the position of equilibrium will shift to minimise the change

Question 4

what three factors alter the position of equilibrium

Answer 4

-concentration of the reactants or products
-pressure in reactions involving gases
-temperature

Question 5

what is the effect of temperature on equilibrium

Answer 5

the effects of temperature on equilibrium depends on the enthalpy sign of a reaction
forward reaction is exothermic, reverse reaction is endothermic
equilibrium will shift in a direction that counteracts the change applied:
- increase in temperature will favour an endothermic reaction (temp decrease)
- decrease in temperature will favour an exothermic reaction ( temp increase)

Question 6

what is the effect of concentration on equilibrium

Answer 6

increasing the concentration of a REACTANT will cause equilibrium to move in the direction which decreases the increased reactant concentration
(position of equilibrium will move to the right hand side of an equation forming more products in a reaction)

increasing the concentration of a PRODUCT will cause equilibrium to move in the direction that decreases the increased product concentration
(position of equilibrium moves to the left hand side of an equation forming more reactants in a reaction)

Question 7

how do you write the equilibrium constant Kc expression
(where are products, reactants and powers)

Answer 7

products are on the top line
reactants are on the bottom line
the power you raise the concentration of a substance to is the same as the number in front of the balanced equation
e.g.
aA + bB ==== cC +dD (at constant temp)

expression for Kc = [C]c [D]d
[A]a [B]b

Question 8

what are the relation of position of equilibrium to size of Kc

Answer 8

Kc > 1 there are more products than reactants at equilibrium
Kc&raquo_space; 1 (greater than 10 to the power of 10) means the reaction seems to have gone to completion
Kc < 1 there are more reactants than products
Kc &laquo_space;1 (less than 10 to the power of minus 10) means the reaction seems to have never of occurred