Topic 7.1: Equilibrium

Question 1

Definition of Dynamic Equilibrium

Answer 1

State in which the rate of the forward reaction equals the rate of the backward reaction

Question 2

Characteristics of equilibrium

Answer 2

a) Dynamic
b) Attained in a closed system
c) Constant concentration of reactants and products
d) No change in macroscopic properties
e) Achieved from either direction

Question 3

Characteristics of equilibrium (Explanation)

a) Dynamic

Answer 3

The reaction has stopped but both forward and backward reactions are still occurring at the same rate.

Question 4

Characteristics equilibrium (Explanation)
b) Attained in a closed system

Answer 4

A closed system prevents exchange of matter with the surroundings, so it is achieved where both reactants and products can react and recombine.

Question 5

Characteristics equilibrium (Explanation)
c) Constant concentrations of reactants and products

Answer 5

They are being produced and destroyed at an equal rate.

Question 6

Characteristics equilibrium (Explanation)
d) No change in macroscopic properties

Answer 6

Color and density do not change as these depend on the concentrations.

Question 7

Characteristics equilibrium (Explanation)
e) Achieved from either direction

Answer 7

The reaction can be started with all reactants, all products or a mixture.

Question 8

Example of physical equilibrium

Answer 8

a) In a closed system, Br2 (l) is in a dynamic equilibrium with its vapor.
b) There will always be both liquid and gas bromine in the flask.
c) Vaporization and condensation are both happening simultaneously in the flask.
d) Liquid bromine is in dynamic equilibrium with bromine vapour.

Question 9

Example of chemical equilibrium

Answer 9

a) In a closed system, the rate of disassociation of HI is fastest at the start.
b) The reverse reaction, which initially has a zero-rate due to the lack of products, starts slowly and increases in rate as the concentrations of products increases.
c) The rate of disassociation of HI has become equal to the rate of the reverse reaction of association between H2(g) + I2 (g), so the concentrations remain constant.

Question 10

Representation of Equilibrium Reaction

Answer 10

aA + bB ⇄ cC+ dD

Question 11

Definition of the Equilibrium Constant

Answer 11

Ratio of concentrations of products over reactants for a reaction that is at equilibrium

Question 12

Representation of Equilibrium Constant (Kc)

Answer 12

([C]^c {D]^d) / ([B]^b {A]^a)

Question 13

What does the magnitude of Kc represent?

Answer 13

The extent of a reaction at equilibrium (Relative amounts of products or reactants)

Question 14

If Kc&raquo_space; 1, then equilbirium favors…

Answer 14

Products

Question 15

If Kc &laquo_space;1, then equilbirium favors…

Answer 15

Reactants

Question 16

What would happen to the value of Kc for a particular reaction at a particular temperature if an environmental factor is modified?

Answer 16

Remains constant. THe system adjusts to keep the concentrations at equilibrium

Question 17

What does the Chatelier’s principle state?

Answer 17

If a dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium shifts to counteract the change to re-establish an equilibrium:

Question 18

What happens to the position of equilibrium if the pressure increases in a system?

Answer 18

It shifts the equilibrium to the side with fewer moles of gas

Question 19

What happens to the position of equilibrium if the pressure decreases in a system?

Answer 19

It shifts the equilibrium to the side with more moles of gas

Question 20

What happens to the position of equilibrium if a substance is added to a system at equilibrium?

Answer 20

The system reacts to consume some of the substance.

Question 21

What happens to the position of equilibrium if a substance is removed from a system?

Answer 21

The system reacts to produce more of substance.

Question 22

What happens to the position of equilibrium if a catalyst is added to a system?

Answer 22

No effect

Question 23

What happens to the position of equilibrium if temperature is increased in a system?

Answer 23

The position of equilibrium shifts in the endothermic direction

Question 24

What happens to the position of equilibrium if temperature is decreased in a system?

Answer 24

The position of equilibrium shifts in the exothermic direction.

Question 25

Which environmental factor changes the value of Kc?

Answer 25

Temperature

Question 26

How does temperature change the value of Kc for an exothermic reaction?

Answer 26

Kc decreases as the temperature is increased.

Question 27

How does the temperature change the value of Kc for an endothermic reaction?

Answer 27

Kc increases as the temperature is increased.

Question 28

Manipulation of Kc

a) Inverse reaction
b) Multiple of a reaction
c) Adding two reactions

Answer 28

a) 1 / K
b) K^n
c) (K1) (K2)

Question 29

What does the reaction quotient measure?

Answer 29

Relative amounts of products and reactants present during a reaciton at a particular point in time.

Question 30

Purpose of comparing Kc with Q

Answer 30

Determine the direction of the reaction

Question 31

If Kc = Q, then…

Answer 31

The reaction is at equilibrium

Question 32

If Kc > Q, then…

Answer 32

Q will increase and produce more products.

Question 33

If Kc < Q, then…

Answer 33

Q will decrease and therefore create more reactants.

Question 34

Chemical equation of Haber process

Answer 34

N2(g) + 3H2(g) ⇄ 2NH3(g)

Question 35

Information of Haber process (3)

Answer 35

(a) All reactants and products are gases
(b) The forward reaction is exothermic so releases heat.
(c) Fe works as a catalyst