Unit 5

Question 1

What is an exothermic reaction?

Answer 1

Transfers thermal energy to the surroundings leading to an increase in the temperature of the surroundings

Question 2

What is an endothermic reaction?

Answer 2

Takes in thermal energy from the surroundings leading to a decrease in the temperature of the surroundings

Question 3

What is the transfer of thermal energy during a reaction called?

Answer 3

Enthalphy change /\H. It is negative for endothermic reactions - and positive for endothermic reactions

Question 4

What is activation energy?

Answer 4

The minimum energy that colliding particles must have to react

Question 5

Bond breaking is a _______ process?

Answer 5

Bond breaking is an endothermic process. The enthalpy change is positive, due to thermal energy being taken IN (absorbed)

Question 6

Bond making is a _________ process?

Answer 6

Bond making is an exothermic process. The enthalpy change will be negative, due to energy being released

Question 7

What is the differences between physical change and chemical changes?

Answer 7

Physical changes involve changes in states of matter, while chemical changes produce new substances - involve atomic-level reactions

Question 8

What is collision theory?

Answer 8

The number of particles per unit volume collide with each other and react only when reactant particles collide with sufficient energy to react. If they have insufficient energy they just bounce off each other

Question 9

5 Factors affecting rate of reaction:

Answer 9

1. Concentration
2. Pressure
3. Changing the surface area of solides
4. Temperature
5. Catalyst

Question 10

What does a catalyst do?

Answer 10

Increases the rate of reaction, and is unchanged at the end of the reaction. It decreases the activation energy of a reaction

Question 11

Practical methods for investigating the rate of reaction:

Answer 11

1. Change in mass of a reactant/product
2. Formation of gas

Question 12

How are reversible chemical reactions shown?

Answer 12

⇌ with this symbol

Question 13

A reversible reaction in a closed system is at equilibrium when:

Answer 13

1. the rate of the forward reaction is equal to the rate of the reverse reaction
2. the concentrations of reactants and products are no longer changing