Reverse reactions and equilibrium Term 1

Question 1

Define reverse reactions.

Answer 1

When products, once formed, can react again to form new reactants.

Question 2

Examples of principle of reversibility

Answer 2

phase changes, dissolution of gases, precipitation and dissolution of ionic solids

Question 3

Define an open system.

Answer 3

Matter and energy can be exchanged with the surroundings

Question 4

Define a closed system

Answer 4

Energy can be exchanged with surroundings but matter can not

Question 5

Define an irreversible reaction

Answer 5

When products cannot be converted back to reactants

Question 6

What is the principle of reversibility

Answer 6

An elementary reaction can occur in both forward and reverse directions

Question 7

Examples of reverse reactions

Answer 7

evaporation and condens., saturated sugar solution, reaction of haemoglobin

Question 8

Describe reaction between haemoglobin and oxygen

Answer 8

reversible reaction

Question 9

Describe evaporation and condensation reaction

Answer 9

reversible reaction

Question 10

Describe saturated sugar reaction to form a solution

Answer 10

reversible reaction

Question 11

Define dynamic equilibrium

Answer 11

A continual exchange

Question 12

What must occur during equilibrium?
(x4)

Answer 12

-closed system
-rate of fwd and reverse reaction are =
-constant composition
-Kc value dependent on temperature

Question 13

Difference between extent of reaction and rate of reaction

Answer 13

extent indicates how much product is formed at eqm where as rate is a measure of the change in concentration of the reactants and products with time

Question 14

Equation for Kc

Answer 14

eqm constant
aA+bB—-><— cC+dD
k= [C]^c x [D]^d / [A]^a x [B]^b

Question 14

Equation for Kc. Qc?

Answer 14

eqm constant
aA+bB—-><— cC+dD
k= [C]^c x [D]^d / [A]^a x [B]^b
same reaction can be used to find reaction quotant when reaction not at eqm

Question 15

What is meant when reactant is favoured in relation to Kc value

Answer 15

value will be less than 1

Question 16

What is LeChateliers principle

Answer 16

when a change is applied to a system in dynamic eqm the composition of the eqm mixture will alter in such a way as to counteract that change

Question 17

What occurs to Kc when inert gas added

Answer 17

no change

Question 18

What factors effect eqm and how

Answer 18

Concentration of reacs and prods
-Kc stays same
-eqm shifts
Pressure
-Kc stays same
-increase in pressure pushes reaction to side with less gas particles
Temperature
-Kc alters
-greater effect to endothermic

Question 19

Define eqm yield

Answer 19

the amount of products present at eqm

Question 20

Example of explaining equilibrium when subject to concentration increase
N2O4—>2NO2

Answer 20

1. Forwards rate increases due to an increase in concentration of N204. The particles per unit volume increases therefore increasing the frequency of collisions per unit time.
2. The concentration of NO2 has remained the same meaning a backwards reaction rate doesn’t change therefore there is a net forward reaction
3. The concentration of N204 will decrease as consumed therefore the forwards rate decreases as there is less particles per unit volume. The concentration of 2NO2 will increase as N2O4 consumed so the rate of bwd reaction will increase
4. Until rates are equal and eqm occurs

Question 21

Example of explaining equilibrium when subject to pressure increase
2NO2—>N2O4

Answer 21

1. Increase in pressure will cause an increase in gas particle sper unit volume. This will equal more collisions per unit time, therefore increasing the rate of successful collision. This means both rates of reaction increase for both reactions.
2. Because 2NO2 has more gas molecules, the forwards reaction will be effect more by the increase in pressure, rate of forward reaction will increase more=net fwd reaction
3. As 2NO2 used up, fwds rate will decrease. As more N2O4 is produced the rate of reverse reaction will increase
4. Until eqm is reached

Question 22

Example of explaining equilibrium when subject to temperature decrease (exothermic reaction in this case)
2NO2—>N2O4

Answer 22

1. decrease in temperature=decrease in average kinetic energy of particles. This will decrease the frequency of successful collisions therefore decreasing both rates
2. The endothermic reaction will decrease more, therefore the rate of bwd reaction will decrease more=net forward reaction
3. As NO2 is consumed, fwd rate decreases, as N2O4 produced, bwd rate will increase
   4.Until eqm is reached

Question 23

How does decrease in volume effect equilibrium

Answer 23

1. Pressure is inversely proportional to the volume of a container. Therefore, decrease volume will increase the pressure
2. This will cause an increase in gas particles per unit volume equalling more collisions per unit time, therefore increasing the rate of successful collision. This means both rates of reaction increase for both reactions.
3. The substance with more gas molecules, will be effected more by the increase in pressure, (in this case the reactant) so rate of forward reaction will increase more=net fwd reaction
4. As recatant is used up, fwds rate will decrease. As more product is produced the rate of reverse reaction will increase
5. Until eqm is reached

Question 24

How does a catalyst effect reaction rate and equilibrium

Answer 24

1. Works by providing alternative reaction pathway requiring less activation energy. The addition of a catalyst will lower the activation energy of both the fwd and bwd reactions.
2. Due to this, there will be more successful collision per unit time, therefore increasing the rate of the the fwd and bwds reaction equally.
3. There will be no change to the relative concentration of the products and reactants due to the equal rate so the position of equilibrium will not change.

4.Therefore the value of equilibrium constant will not change.