Enthalpy

Question 1

What is chemical energy?

Answer 1

A form of potential energy that lies within chemical bonds.

Question 2

What are chemical bonds?

Answer 2

The forces of attraction that bind atoms together in compounds.

Question 3

What is enthalpy (H)?

Answer 3

The heat content that is stored in a chemical system.

Question 4

Describe the law of conservation of energy.

Answer 4

The amount of energy that leaves a chemical system is exactly the same as the amount that goes to the surroundings.
- heat loss = heat gain (temp. Inc.)
- heat gain = heat loss (temp. Dec.)

Question 5

What is enthalpy change?

Answer 5

The heat exchange with the surroundings during a chemical reaction, at constant pressure.

Enthalpy (products) - enthalpy (reactants).

Question 6

What makes a reaction exothermic?

Answer 6

• Enthalpy (products) < Enthalpy (reactants)
• heat loss to the surroundings
• enthalpy change is negative
• temp of surroundings increases

Question 7

What makes a reaction endothermic?

Answer 7

• Enthalpy (products) > enthalpy (reactants)
• heat gain from the surroundings
• enthalpy change is positive
• temp of surroundings decreases

Question 8

Name 2 exothermic reactions.

Answer 8

1. Oxidation of fuels
2. Respiration

Question 9

Name 2 endothermic reactions.

Answer 9

1. Thermal decomposition
2. Photosynthesis