equilibrium

Question 1

open system

Answer 1

both matter and energy can be exchanged between systems and surroundings

Question 2

closed system

Answer 2

only energy can be exchanged between systems and surroundings

Question 3

physical changes

Answer 3

change in state; between intermolecular bonds (h-bonds, dipole-dipole, dispersion); reversible

Question 4

chemical change

Answer 4

new substances are formed; intramolecular bonds (metallic, ionic, covalent); some are reversible

Question 5

equilibrium characteristics

Answer 5

1. rate of a forward reaction = rate of a backward reaction
2. equilibrium is ‘dynamic’ in nature, there are no visible/observable changes while changes are constantly taking place at atomic/molecule level

Question 6

equilibrium characteristics

Answer 6

1. rate of a forward reaction = rate of a backward reaction
2. equilibrium is ‘dynamic’ in nature, there are no visible/observable changes while changes are constantly taking place at atomic/molecule level

Question 7

which is greater: Ea of forward reaction or Ea of backward reaction?

Answer 7

Ea of backward reaction; it consumes more energy

Question 8

le chatelier’s principle

Answer 8

if stress/disturbance is applied to system at equilibrium, the system shifts to forward or backward side in order to reestablish the equilibrium

Question 9

examples of disturbances to equilibrium

Answer 9

1. change in conc. of product or reactants
2. change in pressure
3. change in temperature
4. catalyst

Question 10

homogenous equilibrium

Answer 10

reactants and products are all in same state

Question 11

equilibrium law - the equilibrium constant

Answer 11

Kc = [products]^coefficient/[reactants]^coefficient

Question 12

what occurs when a system undergoes a change in concentration?

Answer 12

increase in concentration of reactants shifts the equilibrium to right/forward direction, concentration of reactants decreases and vice versa

Question 13

what occurs when a system undergoes a change in pressure?

Answer 13

increase in pressure shifts the reaction to side with less number of moles and vice versa

Question 14

what do spikes indicate on an equilibrium graph?

Answer 14

change in concentration

Question 15

what do curves indicate on equilibrium graphs?

Answer 15

change in temperature

Question 16

what happens to the equilibrium when a change in temperature occurs? does it remain the same?

Answer 16

establishes a new equilibrium due to faster or slower moving particles

Question 17

what does the symbol with a circle with line straight through the middle represent?

Answer 17

plimsoll; standard state symbol

Question 18

Kc = 1

Answer 18

[P] = [R] ; equilibrium

Question 19

Kc > 1

Answer 19

[P] > [R] ; lies to the left

Question 20

Kc < 1

Answer 20

[P] < [R] ; lies to the right

Question 21

forward reaction

Answer 21

the reaction between reactants to form products

Question 22

reverse reaction

Answer 22

products react to form the reactants

Question 23

enthalpy

Answer 23

the energy stored within chemical substances; chemical energy or heat content

Question 24

activation energy

Answer 24

minimum amount of energy required in a collision for a reaction to occur

Question 25

pH

Answer 25

measure of H+ ion concentration in a solution and therefore a measure of the acidity or alkalinity of a solution.

Question 26

homogenous equilibria

Answer 26

all species are present in the same phase i.e. gas phase or solution reactions

Question 27

heterogenous equilibria

Answer 27

species exist in more than one phase i.e. reactions involving solid and gases or solids and liquids

Question 28

reaction reaches the state of dynamic equilibrium when:

Answer 28

- the reaction is incomplete – it does not consist of only products - bonds are being broken and re-formed constantly; particles never stop moving - the rates of the forward and reverse reactions are equal

Question 29

dynamic equilibrium

Answer 29

the state a reaction reaches when the rates of the forward and reverse reactions are equal

Question 30

concentration

Answer 30

the amount of solute dissolved in a substance

Question 31

temperature

Answer 31

a measure of the average kinetic energy of the particles within a system

Question 32

Le Chatelier’s principle

Answer 32

if an equilibrium system is subjected to a change, the system will adjust itself to partially oppose the effect of the change.

Question 33

pressure

Answer 33

the force exerted per unit area, by one substance upon another substance

Question 34

volume

Answer 34

a measure of the space occupied by a substance

Question 35

inert gas

Answer 35

a gas that has extremely low reactivity with other substances; noble gases

Question 36

catalysts

Answer 36

a substance that increases the rate of reaction by lowering the activational energy without itself being consumed in the reaction

Question 37

complete the sentence: when the reactant concentration is increased...

Answer 37

the system partially opposes the change by moving to the product side to decrease the reactant concentration resulting in a net forward reaction.

Question 38

complete the sentence: when the product concentration is increased...

Answer 38

the system partially opposes the change by moving to the reactant side to decrease the product concentration resulting in a net backward reaction

Question 39

complete the sentence: when the reactant concentration is decreased...

Answer 39

the system partially opposes the change by moving to the reactant side to increase the reactant concentration resulting in a net backward reaction.

Question 40

complete the sentence: when the product concentration is decreased...

Answer 40

the system partially opposes the change by moving to the product side to increase the product concentration resulting in a net forward reaction.

Question 41

why does the concentration remain unchanged in some cases when the pressure is increased?

Answer 41

This is because the same number of reactant and product molecules exist within the same volume of space regardless of the increase in pressure caused by the inert gas

Question 42

do catalysts disturb the equilibrium? why?

Answer 42

no; it only lowers the Ea of the system; enables it to reach equilibrium faster

Question 43

equilibrium law

Answer 43

law that states that the concentration of products to their power of their coefficients, divided by the concentration of reactants to the power of their coefficients is equal to the equilibrium constant (Kc)

Question 44

reaction quotient

Answer 44

Qc; ratio of reactants to products in a reaction when it is not at equilibrium