Mod 5 EQUILIBRIUM AND ACID REACTIONS: Static and dynamic equilibrium

Question 1

True or false: Reversible reactions always reaches completion.

Answer 1

False. The reaction never reaches completion because the products can be re-formed into reactants

Question 2

Describe the process in reversible reactions.

Answer 2

Forward reaction (reactants → products) happens at a fast rate at the beginning but eventually decreases and backward reaction (products → reactants) happens at a slow rate at the beginning but eventually increases (eventually their rates will reach equilibrium)

Question 3

Describe the difference between static equilibrium and dynamic equilibrium

Answer 3

Static equilibrium only allows for reactants to convert to products, with the reactants being completely used up during the reaction, reaching completion.

Dynamic equilibrium allows for the reaction to occur vice versa when enough energy is present to stimulate particles colliding.

Question 4

Identify open, closed, and isolated systems

Answer 4

Open system - both matter and energy leave the system

Closed system - matter is conserved, but energy can still be exchanged with the environment

Isolated system - insulated, both matter and energy are preserved

Question 5

Write the equation for Gibbs Free Energy, identifying what each variable means (include units)

Answer 5

△G = △H - T△S
G - gibbs free energy (measured in J/kJ)
H - enthalpy (measured in J/kJ)
T - temperature (measured in Kelvin)
S - entropy (measured in J/K, joules per kelvin)

Question 6

Identify what is Gibbs Free Energy

Answer 6

Gibbs free energy is the associated with a chemical reaction that can be used to do work.

Question 7

What are the conditions for a chemical reaction to be considered _ _ _ - _ _ _ _ _ _ _ _ _ _ _, _ _ _ _ _ _ _ _ _ _ _, or at _ _ _ _ _ _ _ _ _ _ _, based on the value of the Gibbs free energy change (ΔG) respectibely?

△G > 0, _ _ _ - _ _ _ _ _ _ _ _ _ _ _ (endergonic, work energy is _ _ _ _ _ _ _ _)

△G < 0, _ _ _ _ _ _ _ _ _ _ _ (exergonic, work energy is _ _ _ _ _ _ _ _)

△G = 0, at _ _ _ _ _ _ _ _ _ _ _

Answer 7

△G > 0, [non-spontaneous] (work energy is released)

△G < 0, [spontaneous] (exergonic, work energy is absorbed)

△G = 0, at [equilibrium]

Question 8

Would this reaction occur?
Scenario:

• Forward reaction is exothermic, with negative ∆S
  → driven by favourable enthalpy change (because exothermic means enthalpy change is negative)
• Reverse reaction is therefore endothermic(the opposite of the forward reaction), positive ∆S

Answer 8

Yes, as it is driven by favourable entropy change (because we like when things are messy and disordered)

Question 9

Would this reaction occur?
Scenario:

• Forward reaction is endothermic, positive ∆S

→ Driven by favourable entropy

• Reverse reaction is exothermic, negative ∆S

Answer 9

Yes, as it is driven by favourable enthalpy

Question 10

How would this be thought of as:
(△H = -ve) is an energetically favourable reaction

Answer 10

Think of it as all reactions want to release energy rather than absorb it

Question 11

How would this be thought as:
(△S = +ve) is an entropically favourable reaction

Answer 11

Think of it as you favour messy room over clean room because to clean your room you need to put energy into it

Question 12

Would this reaction occur?
Scenario:

• Forward reaction is exothermic, positive ∆S
  → Drive by both favourable enthalpy and entropy
• Reverse reaction is therefore endothermic, negative ∆S

Answer 12

Reaction will not occur as there is nothing that drives it

Question 13

What are the characteristics of irreversible, non-equilibrium reactions? (Hint: change in enthalpy and entropy)

Answer 13

Irreversible, non-equilibrium reactions have a forward reaction that favors both a change in enthalpy and entropy (∆H < 0 and ∆S > 0). Consequently, their reversion reaction is always non-spontaneous due to both an unfavorable change in enthalpy and entropy (∆H > 0 and ∆S < 0). The Gibbs free energy of these reactions is negative at all temperatures, indicating that they are always spontaneous; thus, the reverse reaction is always nonspontaneous

Question 14

Fill in the blanks:
In an open system, combustion reactions are always _ _ _ _ _ _ _ _ _ _ _ _ because carbon dioxide and water leave the system.

In a closed system, combustion reactions are _ _ _ _ _ _ _ _ _ _ _ _ because carbon dioxide and water do not _ _ _ _ _ due to the reaction having a _ _ _ _ _ _ _ _ change in ∆G at all temperatures

Answer 14

irreversible, irreversible, react, positive

Question 15

Why is it crucial to convert entropy from joules per kelvin per mole (J/K/mol) to kilojoules per kelvin per mole (kJ/K/mol) for accurate calculations?

Answer 15

Converting entropy units from joules to kilojoules ensures consistency in units throughout the calculation process, preventing errors and maintaining accuracy.

Question 16

Fill in the blank:
Photosynthesis requires a lot of light energy (∆H > 0), there is also a _ _ _ _ _ _ _ _ in entropy because the final product produced is a large solid _ _ _ _ _ _ _ molecule (∆S < 0). For this reason, the reaction is _ _ _ - _ _ _ _ _ _ _ _ _ _ _. Theoretically, it wouldn’t occur but a biological _ _ _ _ _ _ _ _ (enzyme that is chlorophyll) initiates this reaction. The _ _ _ _ _ _ _ reaction of photosynthesis does not take place because the activation energy is too _ _ _ _ in the absence of a suitable catalyst. It only occurs in an _ _ _ _ system which means that matter leaves the system and isn’t retrieved back (e.g O2 leaves the system through stomata, pores in leaves).

Answer 16

decrease, glucose, nonspontaneous, catalyst, reverse, high, open

Question 17

State the three rules of collision theory

Answer 17

The particles must:
1. Collide
2. Collide with sufficient kinetic energy (minimum is activation energy)
3. Collide with correct orientation

Question 18

Identify and describe the factors that affect collision rate

Answer 18

Concentration:
- An increased concentration means increased likelihood of successful collisions, increasing reaction rate.
- Decreased concentration means fewer particles that collides, meaning the likelihood of successful collisions happening is small, decreasing reaction rate

Pressure:
- Increased pressure = decreased volume (inversely proportionate to each other).
Meaning that the atoms have higher potential to collide, increasing reaction rate.
- Decreased pressure = increased volume
Less possibility of colliding as particles have more potential positions they could occupy, decreasing reaction rate

Temperature
- Increased temperature increases kinetic energy of particles which speeds the collision rate, increasing reaction rate
- Decreased temperature decreases kinetic energy that slows down particle collision, decreasing reaction rate

Question 19

Define catalyst

Answer 19

A substance that speeds up the reaction rate by lowering activation energy.

Question 20

True or false: Catalysts do not shift the position of equilibrium

Answer 20

True, because catalysts only speeds up the rate of a forward and reverse reaction to the same extent. This does not alternate the position of equilibrium whatsoever