Chapter 2 Chemical Equilibrium ✓

Question 1

What makes a reaction reversible?

Answer 1

Its LOW activation energy

Question 2

What makes a reaction non-reversible?

Answer 2

its HIGH activation energy

Question 3

In which processes (physical or chemical) would you commonly see reversible reactions and give examples?

Answer 3

In physical processes such as, evaporation, condensation, dissolving, crystallising etc.

Question 4

What is a closed system?

Answer 4

A closed system is where energy can enter or leave the system but not matter. A contained with a lid is an example.

Question 5

What is an open system?

Answer 5

An open system is where both energy and matter can enter and leave the system. An unsealed flask is an example.

Question 6

In what system (open or closed) is needed for a reversible reaction to reach equilibrium and why

Answer 6

A closed system because a closed system does not allow matter to enter or leave the system which allow equilibrium to be reached.

Question 7

What happens during evaporation in an open system?

Answer 7

The vapour diffuses into the surroundings, leaving the system, which results in the flask becoming dry.

Question 8

What happens during evaporation in a closed system?

Answer 8

The vapour is produced but cannot leave. It condenses and returns to the liquid phase within the flask

Question 9

Why is evaporation and condensation in a closed system a reversible reaction?

Answer 9

Because water evaporates, then condenses, and the cycle continues.

Question 10

What is dynamic equilibrium?

Answer 10

It is when the forward and reverse reactions occur at the same rate, leading to no observable change in the system.

Question 11

What is equilibrium vapour pressure?

Answer 11

It is the constant pressure exerted by a vapour in equilibrium with its liquid phase.

Question 12

What happens when a reversible reaction is in a closed system?

Answer 12

It reaches equilibrium, where forward and reverse reactions balance each other

Question 13

What happens to the concentration of reactants and products at equilibrium?

Answer 13

They remain constant, but the relative concentrations of reactants and products differ between systems.

Question 14

Do all systems have the same equilibrium composition?

Answer 14

No, some systems favour a high concentration of products, while others favour reactants.

Question 15

What is the equilibrium constant (Kc)?

Answer 15

A numerical value representing the concentration of all species in a system at equilibrium.

Question 16

Write down the general formula for the equilibrium constant expression

Answer 16

page 14

Question 17

What do the coefficients in a balanced chemical equation represent?

Answer 17

The number of atoms or molecules involved in the reaction.

Question 18

Which states of matter are included in the equilibrium constant expression?

Answer 18

Only gases (g) and aqueous (aq) species. Solids and liquids are excluded.

Question 19

What is the only factor that will affect Kc?

Answer 19

Temperature

Question 20

What does a large Kc value indicate?

Answer 20

The equilibrium favours products.

Question 21

What does a small Kc value indicate?

Answer 21

The equilibrium favours reactants.

Question 22

What does a Kc value close to 1 indicate?

Answer 22

Both reactants and products are present in significant amounts at equilibrium.

Question 23

When can Kc be calculated?

Answer 23

When equilibrium has been reached

Question 24

What is the reaction quotient (Qc)?

Answer 24

It measures the relative concentrations of reactants and products at any moment, not just at equilibrium.

Question 25

Does Qc have a constant value?

Answer 25

No, unlike Kc, Qc varies because it is measured at different points before equilibrium is reached.

Question 26

What does Qc tell us about a system?

Answer 26

It indicates whether a reaction will proceed forward or backward to reach equilibrium.

Question 27

What does it mean if Qc = Kc?

Answer 27

The system is at equilibrium.

Question 28

What does it mean if Qc < Kc?

Answer 28

There are more reactants than products, so the reaction will shift forward to reach equilibrium.

Question 29

What does it mean if Qc > Kc?

Answer 29

There are more products than reactants, so the reaction will shift backward to reach equilibrium.

Question 30

What are the three main imposed changes that affect equilibrium?

Answer 30

-Changing the concentration of a species -Changing the total pressure (in a gaseous system) -Changing the temperature

Question 31

What does Le Chatelier’s Principle predict?

Answer 31

It predicts how an equilibrium system will respond to imposed changes but does not explain why.

Question 32

What is Le Chatelier’s Principle?

Answer 32

If a system at equilibrium experiences a change in conditions, it will adjust to establish a new equilibrium that partially counteracts the imposed change

Question 33

What does “partially counteracts” mean in Le Chatelier’s Principle?

Answer 33

The system responds to an imposed change by shifting equilibrium to reduce its effect, but not completely reverse it.

Question 34

What happens if more reactants are added to a system at equilibrium?

Answer 34

The equilibrium will shift toward the products to partially counteract the increase in reactants.

Question 35

What two concepts can be used to explain equilibrium shifts?

Answer 35

Reaction rate and collision theory.

Question 36

which side will it favour if you increase the pressure of a system at equilibrium?

Answer 36

It will favour the side of the equilibrium reaction with the fewer moles of gas

Question 37

What happens if the temperature of an equilibrium system is raised?

Answer 37

It will favour the endothermic process because the system absorbs the added heat to counteract the change

Question 37

Which side will it favour if you increase the pressure of a system at equilibrium?

Answer 37

It will favour the side of the equilibrium with the greatest moles of gas

Question 38

What happens if the temperature of an equilibrium system is lowered?

Answer 38

It will favour the exothermic process because the system will release heat to counteract the change

Question 39

What does it mean when a reaction is "favoured"?

Answer 39

It means the equilibrium shifts in that direction, increasing the concentration of species on that side and producing more of those substances

Question 40

In the equilibrium reaction: N2 (g) + 3H2 (g) ⇌ 2NH3 (g) ΔH= -92kJ/mol What happens when the temperature is increased?

Answer 40

The system will favour the reverse (endothermic) reaction to absorb the added heat. So more N2 and H2 are produced and less NH3 is formed.

Question 41

In the equilibrium reaction: N2 (g) + 3H2 (g) ⇌ 2NH3 (g) ΔH= -92kJ/mol What happens when the temperature is decreased?

Answer 41

The system will favour the forward (exothermic) reaction to release heat. So, more NH3 is produced and less N2 and H2.

Question 42

What does a catalyst to in a equilibrium reaction?

Answer 42

It will increase the rate of both the forward and reverse reaction

Question 43

What is a greenhouse gas?

Answer 43

Gases in the Earth’s atmosphere that traps heat.

Question 44

What is climate change?

Answer 44

The long-term alteration of global climate patterns, mainly caused by increased greenhouse gas emissions from human activities such as burning fossil fuels.

Question 45

Most marine organisms are what blooded?

Answer 45

Cold-blooded (ectothermic) which means that their internal body temperature is the same as their environment

Question 46

What is coral bleaching?

Answer 46

When corals expel the symbiotic algae in their tissues due to stress (usually from heat), causing them to turn white and become more vulnerable to death.

Question 47

What does anthropogenic mean?

Answer 47

Environmental change caused or influenced by people, either directly or indirectly

Question 48

What is ment by the ocean being a carbon sink?

Answer 48

The ocean absorbs atmospheric gases like CO₂, N₂, and O₂, helping to moderate changes in atmospheric concentrations, especially anthropogenic CO₂.

Question 49

What happens when atmospheric CO₂ increases?

Answer 49

More CO₂ dissolves in the ocean, shifting equilibrium to form more carbonic acid (H₂CO₃), which then dissociates into H⁺ and HCO₃⁻ ions.

Question 50

How does increased CO₂ affect ocean pH?

Answer 50

It causes ocean acidification by increasing H⁺ ion concentration, lowering the ocean's pH.

Question 51

Write the chemical equilibrium series that describes CO₂ dissolving in the ocean.

Answer 51

CO₂(g) ⇌ CO₂(aq) CO₂(aq) + H₂O(l) ⇌ H₂CO₃(aq) H₂CO₃(aq) ⇌ H⁺(aq) + HCO₃⁻(aq) HCO₃⁻(aq) ⇌ H⁺(aq) + CO₃²⁻(aq)

Question 52

What impact does ocean acidification have on calcifying species?

Answer 52

It reduces carbonate ion (CO₃²⁻) concentration, making it harder for organisms like corals and shellfish to form calcium carbonate (CaCO₃) skeletons and shells.

Question 53

How does equilibrium shift when CO₂ concentration increases?

Answer 53

The system favours the forward reaction, increasing H₂CO₃ and H⁺ concentrations, lowering pH.

Question 54

Why does coral bleaching occur with warmer water and lower pH?

Answer 54

Higher temperatures and acidified water stress corals, causing them to expel symbiotic algae and lose colour and nutrients, leading to coral death.

Question 55

How do ocean floor sediments help reduce ocean acidification, and why is their effect limited?

Answer 55

Sediments contain calcium carbonate, which can dissolve to release carbonate ions that neutralise excess H⁺ and reduce acidity. However, this process is very slow and cannot keep up with the rapid increase in acidification caused by rising atmospheric CO₂.

Question 56

Why does a higher [H⁺] concentration reduce [CO₃²⁻] in ocean water?

Answer 56

Extra H⁺ reacts with carbonate ions (CO₃²⁻) to form more hydrogen carbonate (HCO₃⁻), reducing the availability of CO₃²⁻ for organisms that need it to make shells and skeletons.

Question 57

How does Le Chatelier’s Principle explain the effect of increased atmospheric CO₂ on ocean equilibrium?

Answer 57

Adding CO₂ shifts the equilibrium to the right to reduce the stress, forming more H₂CO₃, H⁺, and HCO₃⁻, which increases acidity and lowers [CO₃²⁻].

Question 58

What long-term danger does ocean acidification pose to marine life?

Answer 58

It can weaken or dissolve calcium carbonate structures in marine organisms, reducing their survival, and disrupting entire marine food chains and ecosystems.

Question 59

What causes coral bleaching, and how is it linked to atmospheric CO₂?

Answer 59

Coral bleaching happens when corals are stressed by warmer temperatures and lower pH, causing them to expel their symbiotic algae. Both rising CO₂ and global warming contribute to this stress.

Question 60

Why is the increase in [H⁺] greater than the increase in [HCO₃⁻] when CO₂ dissolves in seawater?

Answer 60

Because H⁺ concentration is initially extremely low, even a small production of H⁺ causes a large relative (factor) increase, whereas HCO₃⁻ is already more concentrated.

Question 61

How does the equilibrium system respond when H⁺ is added from extra CO₂?

Answer 61

The system partially shifts left (reverse reaction) to reduce [H⁺], but the shift is not enough to prevent overall acidification.

Question 62

What are calcifying species?

Answer 62

Organisms that use calcium carbonate to build their hard parts, such as shells and skeletons

Question 63

Why do calcifying species rely on a constant pH and carbonate ions concentration?

Answer 63

Because they need carbonate (CO₃²⁻) and calcium (Ca²⁺) ions to form calcium carbonate (CaCO₃) for their shells and skeletons. A constant pH keeps carbonate levels high. If pH drops, carbonate ions decrease, making shell-building harder, more energy-demanding, and increasing the risk of shell dissolution.