Energy changes

Question 1

what is the definition of an exothermic reaction

Answer 1

an exothermic reaction is a reaction which transfers energy to the surroundings / a reaction in which the reactants store more energy than the products

Question 2

are neutralisation reactions exothermic or endothermic

Answer 2

neutralisation reactions are exothermic

Question 3

give one example of an everyday use of an exothermic reaction and one example of an everyday use of an endothermic reaction

Answer 3

exothermic:
- self heating cans
- hand warmers
endothermic:
sport injury packs

Question 4

suggest, in terms of the storage and transfer of energy, why melting is an endothermic process

Answer 4

melting is endothermic because a substance in the liquid state stores more energy than the same substance in the solid state, so energy is taken in during the reaction

Question 5

give two ways to insulate a reaction mixture when measuring a temperature change

Answer 5

• mix the reagents in a polystyrene cup
• surround the reaction vessel with cotton wool
• put a lid on the reaction vessel

Question 6

if you calculate the overall change in bond energy for an exothermic reaction, would you expect it to be positive or negative

Answer 6

negative
in an exothermic reaction more energy is given out forming the bonds in the products than is taken in breaking the bonds in the reactants

Question 7

a student says “if the products of a reaction contain more bonds than the reactants, the products must have a higher total bond energy”
explain why this statement is not true

Answer 7

the total bond energy does not just depend on the number of bonds. different bonds have different bond energies depending on the strength of the bond, so a small number of strong bonds could have a greater energy than a large number of weak bonds