Chapter 5 - Chemical energetics

Question 1

What is an exothermic reaction?

Answer 1

Exothermic reactions transfers thermal energy to the surroundings leading to an increase in temperature of the surroundings.

Question 2

What is an endothermic reaction?

Answer 2

Endothermic reactions takes in thermal energy from the surroundings leading to a decrease in the temperature of the surroundings.

Question 3

What is a reaction pathway diagram?

Answer 3

Reaction pathway diagrams are graphical representations of the relative energies of the reactants and products in chemical reactions. Progress is shown the on the x axis, energy is shown on the y axis. The difference in height between the energy of reactants and products is the overall energy change of a reaction.

Question 4

What is enthalpy change?

Answer 4

Enthalpy change is the transfer of thermal energy during a reaction, ΔH. It is negative for exothermic reactions and positive for endothermic reactions.
Enthalpy change = energy taken in – energy given out. If this number is negative, it is exothermic because more energy is going out but if this number is positive, it is endothermic because more energy is going in.
Bond breaking is an endothermic process and bond making is an exothermic process.

Question 5

What is activation energy?

Answer 5

Activation energy is the minimum amount of energy required for a successful collision

Question 6

Exothermic diagram showing activation energy and a negative enthalpy change

Answer 6

Question 7

Endothermic diagram showing activation energy and a negative enthalpy change

Answer 7