Chemical Energy

Question 1

How do catalysts affect the reaction rate?

Answer 1

Adding a catalyst will lower the activation energy - therefore more particles will reach it.

Question 2

What is enthalpy?

Answer 2

A measure of the chemical energy in a substance (measured in kJ)

Question 3

Describe the term exothermic:

Answer 3

• releases heat energy to the surroundings
• It may require excess heat to be removed to prevent extreme temperature rises or dangerous conditions.

Question 4

Describe the term endothermic:

Answer 4

• takes in heat energy from the surroundings.
• There may be costs involved in supplying heat at the start of the reaction and also in maintaining the reaction rate.

Question 5

What does enthalpy of combustion mean?

Answer 5

It is the energy change when one mole of the substance burns completely in oxygen.

Question 6

What does Hess’s law state?

Answer 6

That the enthalpy change for a reaction depends on the initial and final states of the reaction and is independent of the route the reaction occurs.

Question 7

What is a molar bond enthalpy?

Answer 7

Molar bond enthalpy is the energy required to break one mole of bonds in a diatomic molecule.

Question 8

What is a mean molar bond enthalpy?

Answer 8

Mean molar bond enthalpy is the energy required to break one mole of bonds that occur in compounds (not diatomic).