Module 3, Section 2

Question 1

What are the characteristics of an exothermic reaction?

Answer 1

Gives out energy, bond formation. Delta H is negative

Question 2

What are the characteristics of an endothermic reaction?

Answer 2

Absorbs energy, bond breaking. Delta H is positive

Question 3

Define standard enthalpy of formation.

Answer 3

The enthalpy change when 1 mole of a substance is formed from it’s elements in their standard states and under standard conditions.

Question 4

Define standard enthalpy change of combustion.

Answer 4

Enthalpy change when 1 mole of a compound is completely burnt in oxygen, under standard conditions

Question 5

What is the calculation used when given enthalpies of formation?

Answer 5

Products - Reactants

Question 6

What is the calculation used when given enthalpies of combustion?

Answer 6

Reactants - Products

Question 7

Why would delta H be positive?

Answer 7

More energy required when breaking bonds than energy released when forming bonds.

Question 8

Define activation energy.

Answer 8

Minimum amount of kinetic energy particles need to react

Question 9

What is the role of a catalyst?

Answer 9

Increases rate of reaction by providing an alternative reaction pathway with a lower activation energy, so more particles have at least the activation energy.

Question 10

What does a heterogenous catalyst do?

Answer 10

Different physical state to reactants. Reaction happens on surface of catalyst, so an increase in surface area of catalyst, means an increase in the number of molecules reacting at the same time, increasing rate of reaction.

Question 11

What does a homogenous catalyst do?

Answer 11

Same physical state as reactants. Forms intermediate species, catalyst combines with reactant to make intermediate, which reacts to form products and reform catalyst.

Question 12

What does le Chatelier’s principle state?

Answer 12

If there’s a change in concentration, pressure or temperature, equilibrium moves to help counteract change

Question 13

What happens to equilibrium with an increase in temperature?

Answer 13

Equilibrium shifts in endothermic direction to absorb heat

Question 14

What happens to equilibrium with a decrease in temperature?

Answer 14

Equilibrium shifts in the exothermic direction to release heat

Question 15

What does a larger value of Kc mean?

Answer 15

Further equilibrium lies to right, more products.

Question 16

What does a smaller value of Kc mean?

Answer 16

Further equilibrium lies to left, more reactants.