4.5.1 Energy changes (must know) PAPER 1

Question 1

What is conservation of energy

Answer 1

Energy is conserved in chemical reactions. The amount of energy in the universe at the end of a chemical reaction is the same as before the reaction takes place. If a reaction transfers energy to the surroundings the product molecules must have less energy than the reactants, by the amount transferred.

Question 2

What is an exothermic reaction

Answer 2

An exothermic reaction is one that transfers energy to the surroundings so the temperature of the surroundings increases.

Question 3

What is an endothermic reaction

Answer 3

An endothermic reaction is one that takes in energy from the

surroundings so the temperature of the surroundings decreases.

Question 4

Examples of exothermic reactions

Answer 4

Exothermic reactions include combustion, many oxidation reactions
and neutralisation.

Everyday uses of exothermic reactions include self-heating cans
and hand warmers

Question 5

Examples of endothermic reactions

Answer 5

Endothermic reactions include thermal decompositions and the reaction of citric acid and sodium hydrogencarbonate.
Some sports injury packs are based on endothermic reactions.

Question 6

What is activation energy

Answer 6

The minimum amount of energy that particles must have to react

Question 7

Draw diagram for exothermic reaction

Answer 7

google answer

Question 8

Draw diagram for endothermic reaction

Answer 8

google answer

Question 9

What do bond energies calculate

Answer 9

The energy needed to break bonds and the energy released when bonds are formed can be calculated from bond energies.

The difference between the sum of the energy needed to break bonds in the reactants and the sum of the energy released when bonds in the products are formed is the overall energy change of the reaction.

Question 10

Where is most energy released from in exothermic reactions (bond energy)

Answer 10

In an exothermic reaction, the energy released from forming new bonds is greater than the energy needed to break existing bonds.

Question 11

Where is most energy released from in endothermic reactions (bond energy)

Answer 11

In an endothermic reaction, the energy needed to break existing bonds is greater than the energy released from forming new bonds

Question 12

Formula to work out overall energy change in bond energy calculations

Answer 12

Energy change = energy of bond breaking - energy of bond making