Enthalpy changes

Question 1

What does the law of conversation of energy state and how does it relate to a chemical reaction?

Answer 1

• Energy cannot be created or destroyed.
• Energy is transferred between the system and its surroundings.
  - System is the chemicals - reactions and chemicals.
  - Surroundings are the apparatus, laboratory, everything that’s not the chemical system.
• Universe = system + surroundings

Question 2

What is the meaning of enthalpy?

Answer 2

• Measure of the heat energy in a chemical system.
• The energy stored between bonds.
• Enthalpy cannot be measured, however enthalpy changes can be.

Question 3

How would you explain what activation energy is?

Answer 3

• Ea
• The minimum input of energy required to break bonds and form new ones in a reaction.

or

• Minimum amount of energy required for a reaction to take place.

Question 4

Why are there standard conditions?

Answer 4

• Chemists use this when doing physical measurements such as
  1. Pressure
  2. Temperature
  3. Enthalpy change