Energy changes revision (2.4)

Question 1

DESCRIBE endothermic reactions + when they occur.

Answer 1

• Endothermic reactions absorb energy in the form of heat from their surroundings.
• Energy is absorbed when bonds are broken.

Question 2

DESCRIBE exothermic reactions + when they occur.

Answer 2

• Exothermic reactions release energy in the form of heat, light or sound into the surroundings of the system.
• Energy is released whenbonds are formed.

Question 3

Define enthalpy.

Answer 3

Enthalpy is the heat content (energy) in a chemical system (symbol H).

Question 4

What is (triangle)rH?

Answer 4

It is the enthalpy change for a reaction.

Question 5

What does Ea stand for?

Answer 5

The activation energy of a reaction.

Question 6

What do you need to label in an energy diagram?

Answer 6

1. The type of reaction
2. The reaction progress (x axis)
3. The potential energy (y axis)
4. The reactants
5. The products
6. The activation energy
7. The change in energy.

Question 7

What does the change in energy look like in an exothermic reaction?

Answer 7

The products will have less energy than the reactants, resulting in a negative energy change.

Question 8

What does the change in energy look like in an endothermic reaction?

Answer 8

The products will have more energy than the reactants, resulting in a positive energy change.

Question 9

What are energy diagrams?

Answer 9

Energy diagrams show the change in enthalpy for a specific reaction.

Question 10

How do you calculate the change in enthalpy?

Answer 10

(triangle)rH = Hproducts - Hreactants