Energetics

Question 1

what is an exothermic reaction?

Answer 1

heat energy is released to make bonds, which increases the temperature of the surroundings (and the reaction mixture)

Question 2

what is and endothermic reaction?

Answer 2

heat energy is needed to break bonds, which decreases the temperature of the surroundings (and the reaction mixture) as the system takes in heat

Question 3

describe a calorimetry experiment for combustion

Answer 3

• combustion is a simple calorimetry experiment to measure the heat released from a burning fuel
• a calorimeter is used to compare the amount of heat energy released by the combustion of different fuels
  1. measure cold water into a calorimeter (a metal or glass container)
  2. record the starting temperature of the water
  3. heat the water using the flame from the burning fuel
  4. record the final temperature of the water
  5. to make your calorimetry reliable, you should repeat the experiment and take an average of temperature rise
  the fuel that produces the largest temperature rise release the most energy per gram of fuel

Question 4

what does ΔH mean?

Answer 4

the symbol that represents the energy or enthalpy change

Question 5

what will ΔH be for an exothermic reaction?

Answer 5

a negative value as it loses heat

Question 6

what will ΔH be for an endothermic reaction?

Answer 6

a positive value as it gains heat

Question 7

what is the bond energy?

Answer 7

the energy required to break a bond is know as the bond energy. It is usually measured in kilojoules per mole of bond (kK/mol)

Question 8

what reaction breaks bonds?

Answer 8

breaking bonds takes in energy (endothermic)

Question 9

what reaction makes bonds?

Answer 9

creating bonds gives out energy (exothermic)

Question 10

what is combustion?

Answer 10

the process of burning something

Question 11

what is calorimetry?

Answer 11

to measure the amount of heat