Chemical energetics

Question 1

Meaning of exothermic and endothermic reactions

Answer 1

• Exothermic: heat is released into the surroundings, transfer of energy to the surroundings. Ex: ​combustion,​ ​many​ ​oxidation reactions​ ​and​ ​neutralisation,​ ​hand​ ​warmers.
• Endothermic: Energy taken in from surroundings, heat taken in. Ex: thermal​​ decomposition, r​eaction​​ of citric​ ​acid​ ​and​ ​sodium​ ​hydrogen carbonate.

Question 2

Bond breaking as an endothermic process and bond forming as an exothermic process

Answer 2

buses ​​take​​ many ​r​outes​’ (​break ​​bonds -​​ take ​​in ​​energy,​​make​​ bonds- release​ ​energy). Thus bond breaking is endothermic and bond forming is exothermic process

Question 3

Energy level diagrams showing

Answer 3

…

Question 4

Calculate the energy of a reaction using bond energies

Answer 4

Enthalphy change:

ΔH = Energy required to break bond - Energy required to form the bond.

Question 5

Activation Energy

Answer 5

Minimum amount of energy required for the reaction to take place.

Question 6

Release of heat energy by burning fuels

Answer 6

Burning​ ​fuels​ ​(i.e.​ ​combustion)​ ​releases​ ​heat​ ​energy
o Reacting​ ​fuels​ ​with​ ​oxygen​ ​/​ ​oxidation​ ​of​ ​fuels

Question 7

use of hydrogen as a fuel

Answer 7

Hydrogen​ ​can​ ​be​ ​used​ ​as​ ​a​ ​fuel​ ​(can​ ​be​ ​burnt​ ​to​ ​produce​ ​energy)

Question 8

The use of hydrogen as a fuel reacting with oxygen to generate electricity in a fuel cell.

Answer 8

Use​ ​of​ ​hydrogen​ ​as​ ​a​ ​fuel:

• Oxidised​ ​(reacted​ ​with​ ​oxygen)​ ​within​ ​the​ ​fuel​ ​cell​ ​to​ ​produce​ ​a​ ​potential difference
• Overall​ ​reaction​ ​in​ ​a​ ​hydrogen​ ​fuel​ ​cell​ ​involves​ ​the oxidation​ ​of​ ​hydrogen to​ ​produce​ ​water
• Fuel​ ​cell​ ​involves​ ​the​ ​reaction​ ​of​ ​a​ ​fuel​ ​(in​ ​this​ ​case:​ ​hydrogen)​ ​with oxygen to produce electricity

Question 9

radioactive isotopes, such as 235U, as a

source of energy

Answer 9

● Radioactive​ ​isotopes​ ​can​ ​be​ ​used​ ​as​ ​a​ ​source​ ​of​ ​energy
● Nuclear​ ​power​ ​stations​ ​use​ ​fission​ ​of​ ​e.g.​ ​uranium​ ​to​ ​generate​ ​heat