Energy Changes

Question 1

Exothermic reaction examples

Answer 1

• Combustion
• Oxidation
• Neutralisation

(Sodium hydroxide solution into hydrochloric acid, thermometer goes up.)

Question 2

Endothermic reaction examples

Answer 2

• Thermal decompostition
• Reaction of ethanoic acid and sodium carbonate

(Sodium carbonate powder into ethanoic acid, thermometer goes down.)

Question 3

(Bonds) During a chemical reaction:

Answer 3

• Bonds in the reactants are broken
• New bonds are made in the products
• A reaction is exothermic if more heat energy is needed to make the bonds than break them
• A reaction is endothermic if more heat energy is needed to break the bonds than make them

Question 4

Bond Energy

Answer 4

• A bond energy is the amount of energy required to break one mole of a particular covalent bond.
• To figure out the bond energy, add the reactants (energy in) and producst (energy out) seperately. Then subtract the ‘in’ from ‘out’.
• If the number is negative, the reaction is exothermic.