LECTURE 2 (Thermodynamics)

Question 1

What is an indication that a chemical reaction has taken place?

Answer 1

New properties become visible

Question 1

What does the Law of conservation of mass state?

Answer 1

Matter is neither created nor destroyed in chemical reactions

Question 2

What happens in Combination reactions?

Answer 2

Two or more elements or compounds bond to form one product

Question 3

What happens in Decomposition reactions?

Answer 3

A reactant splits into two or more simpler products

Question 4

What happens in Replacement reactions?

Answer 4

Elements in a compound are replaced by other elements

Question 5

What happens in Combustion reactions?

Answer 5

A carbon-containing compound burns in oxygen from the air to produce carbon dioxide (CO2), water (H2O) and energy in the form of heat or a flame

Question 6

What happens in Oxidation-Reduction reactions?

Answer 6

Electrons are transferred from one substance to another. If one substance loses electrons, another substance must gain electrons. Oxidation is defines as the loss of electrons, Reduction is the gain of electrons.

Question 7

Describe a Reducing agent

Answer 7

• Loses one or more electrons
• Causes reduction
• Undergoes oxidation
• Becomes more positive (or less -ve)

Question 8

Describe a Oxidising agent

Answer 8

• Gains one or more electrons
• Causes oxidation
• Undergoes reduction
• Becomes more negative (less +ve)

Question 9

What is Kinetic energy?

Answer 9

Energy of motion

Question 10

What is Potential energy?

Answer 10

Stored energy

Question 11

What is the difference between an Endothermic and Exothermic reaction?

Answer 11

Endothermic = Absorbs heat (∆H is positive)

Exothermic = Releases heat (∆H is negative)

Question 12

What is the Heat of reaction (Enthalpy change)?

Answer 12

Energy of bonds formed in products minus energy of bonds broken in reactants

[The difference between the energy absorbed in breaking bonds and the energy released in forming bonds]

Question 13

What is a spontaneous process?

Answer 13

A process that once started proceeds on its own without any external influence

[Events that lead to lower energy tend to occur spontaneously]

Question 14

What is Entropy?

Answer 14

A measure of the amount of molecular disorder in a system

Question 15

What value determines spontaneity?

Answer 15

The value of free-energy ∆G change

Question 16

How do you calculate free energy ∆G change?

Answer 16

∆G = ∆H - T∆S

∆G = Free-energy change
∆H = Enthalpy change
T = temperature
∆S = Entropy change

Question 17

How can you tell a reaction is spontaneous or non-spontaneous?

Answer 17

SPONTANEOUS:
- ∆G is negative
- Free energy is released
- Process is exergonic

NON-SPONTANEOUS:
- ∆G is positive
- Free energy is added
- Process is endergonic

Question 18

What is the difference between exergonic and endergonic?

Answer 18

EXERGONIC = the products are at a lower energy level than the reactants

ENDERGONIC = products are higher than reactants

Question 19

What is important to remember about ∆G?

Answer 19

Just because a chemical reaction has a favourable free-energy change does not mean it occurs rapidly -> Value of ∆G tells us only if it can occur not how fast it will take place or details about the molecular changes

Question 20

What does increase in temperature do?

Answer 20

Increase in temp -> Increase in frequency of collisions -> Increase in forcefulness of collisions -> Increase in reaction rate

Question 21

What is a catalyst?

Answer 21

A substance that accelerates a chemical reaction but is itself unchanged in the process

Question 22

What happens in equilibrium?

Answer 22

Forward and reverse reactions have stopped