equilibrium

Question 1

3 Requirements of collision theory

Answer 1

• Reactants must collide
• Reactants must collide with enough energy to meet the required activation energy
• Reactants must collide with a favourable orientation

Question 2

What are catalysts

Answer 2

Substances that speed up chemical reactions without being consumed by the reaction themselves

Question 3

What is temperature

Answer 3

A measure of the average kinetic energy of the particles in a substance

Question 4

What is pressure

Answer 4

Pressure is a measure of the force that particles in a substance apply to the walls of their container

Question 5

What is concentration

Answer 5

Concentration is a measure of number of particles of a substance per unit volume - refers to aqueous solutions

Question 6

What is Surface Area

Answer 6

Measure of the area of exposed surface of a substance

Question 7

3 Key Characteristics of Equilibrium

Answer 7

• A constancy in macroscopic properties: colour, pressure, temp
• The forward and reverse reaction rates being equal and ongoing - (system is said to be in dynamic equilibrium)
• Tend to have a low activation energy for both the forward and reserve reaction

Question 8

Equilibrium occurs in a closed system. What is a closed system?

Answer 8

where energy can enter or leave and matter cannot

Question 9

What is vapour pressure

Answer 9

described as partial pressure (concentration) of vapour that forms over a liquid in a closed system at a certain temperature

Question 10

What happens when the temperature of a vapour pressure system is raised

Answer 10

• An increase in temperature, More liquid particles have sufficient kinetic energy to leave the liquid phase thus the rate of vaporization increases
• Soon after (as there are more gaseous particles present), the rate of condensation increases until the rate of condensation equals the rate of vaporisation and a new equilibrium is achieved
• At this new equilibrium the volume of liquid will be less and vapour pressure will be higher

Question 11

What happens when the temperature of a vapour pressure system is lowered

Answer 11

• Decreasing temperature, decreases the amount of gas particles that have sufficient kinetic energy to stay in a gaseous state thus, rate of condensation increases
• Soon after, (as there are more liquid particles present) the rate of vaporisation increases until the rate of vaporisation equals the rate of condensation and a new equilibrium is achieved
• At this new equilibrium the volume of liquid will be higher and vapour pressure will be less

Question 12

What happens when the temperature of a solution system is raised

Answer 12

• If temp increased, more solid particles will have sufficient energy to dissolve into the solution and the rate of dissolution increases
• Soon after, (as there are more liquid particles present), the rate of crystallization increases until the rate of crystallization equals the rate of dissolution and a new equilibrium is established
• At this new equilibrium, the amount of solid would be less and the concentration of the solution will be greater

Question 13

What happens when the temperature of a solution system is decreased

Answer 13

• If temp is decreased, this decreases the amount of solution particles that have sufficient kinetic energy to stay in a liquid state thus, rate of crystallisation increases
• Soon after (as there are more solid particles present), the rate of dissolution increases until the rate of crystallization equals the rate of dissolution and a new equilibrium is established
• At this new equilibrium, the amount of solid would be more and the concentration of the solution will be less

Question 14

Which species are included in Kc constant

Answer 14

Only aqueous and gaseous species are included in the equilibrium constant expression

Question 15

Why are solids and liquids not included in the equilibrium constant expression

Answer 15

• This is because the concentrations of solids and liquids are said to be constant from one reaction to the next
• Concentration is said to be related to density and molar mass of which both remain constant

Question 16

What do large Kc values suggest?

Answer 16

Large values suggest that the products have a greater concentration than the reactants - the equilibrium favours the products/lies more so to the right

Question 17

What do small Kc values suggest

Answer 17

Small values suggest that the reactants have a greater concentration than the products - the equilibrium favours the reactants/lies more so to the left

Question 18

What do Kc constants around 1 suggest

Answer 18

concentrations of reactants and products are similar

Question 19

The Kc values for the ionisation of two weak acids are given below. Which is the stronger acid and why?

CH3COOH(aq) + H2O(l) ⇌ CH3COO–(aq) + H3O+(aq)
Kc = 1.82 ×10-5

HCN(aq) + H2O(l) ⇌ CN–(aq) + H3O+(aq)
Kc = 6.23 ×10-10.

Answer 19

• CH3COOH, as it has the higher Kc value which indicates more products present at equilibrium
• As acid strength is based on [H3O+] (concentration of hydrogen ions) in solution, resulting in CH3COOH being the stronger acid

Question 20

What is the Le Chateliers Principle

Answer 20

“If a system at equilibrium is subjected to a change in conditions, the system will re-establish equilibrium in such a way as to partially counteract the imposed change”

Question 21

What does Le Chateliers principle allow us to do

Answer 21

allows us to predict (not explain) the effect changes on a system at equilibrium will have

Question 22

Explain 5 steps of Ocean Equilibria

Answer 22

Ocean acts as a sink for some atmospheric carbon dioxide through the equilibrium:

CO₂(g) ⇌ CO₂(aq)

Some of the dissolved CO₂ can react with water to produce carbonic acid

CO₂ + H₂O ⇌ H₂CO₃

As carbonic acid is a weak acid, it partially ionises to produce hydrogen (or hydronium) ions according to the equilibrium

H₂CO₃ + H₂O ⇌ HCO3- + H₃O+

Furthermore, the hydrogen carbonate ion can partially ionise to produce more hydronium ion according to the equilibrium

HCO3- + H₂O ⇌ CO₃2- + H₃O+

The hydronium ion produced can decrease the pH of the ocean which can increase the dissolving of solid calcium carbonate, found in shells and skeletons of calcifying organisms

CaCO₃ + 2H₃O+ ⇌ Ca2+ + CO₂ + 3H₂O

Question 23

Explain the 2 things which can happen with the free carbonate ions

Answer 23

Free carbonate ions in ocean water that calcifying species use to produce their shells or skeletons can be taken up by excess hydronium ions in water

CO₃2- + H₃O+ ⇌ HCO3- + H₂O

Free carbonate ions can also be used up by the excess CO₂ present in the ocean

CO₃2- + H₂O + CO₂ ⇌ 2HCO3-