C5 - Energy Changes

Question 1

Energy in chemical reactions (3)

Answer 1

• Energy is conserved
• 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

Exothermic reaction (2)

Answer 2

• Is one that transfers energy to the surroundings so the temperature of the surroundings increases
• Exothermic reactions include: combustion, many oxidation reactions and neutralisation

Question 3

Everyday uses of exothermic reactions (2)

Answer 3

• Self-heating cans

* Hand warmers

Question 4

Endothermic reactions (2)

Answer 4

• Is one that takes in energy from the surroundings so the temperature of the surroundings decreases
• Endothermic reactions include: Thermal decomposition and the reaction of citric acid and sodium hydrogencarbonate also some sports injury packs are based on endothermic reactions

Question 5

Required practical - investigate the variables that affect temperature changes in reacting solutions (2)

Answer 5

• Put a polystyrene cup into a beaker of cotton wool to give more insulation and put a lid on the cup to reduce energy lost by evaporation
• Take the temperature of the reagents, mixing them in the cup and then measuring the temperature of the solution at the end

Question 6

How do chemical reactions occur

Answer 6

Can only occur when reacting particles collide with each other and with sufficient energy

Question 7

Activation energy

Answer 7

Is the minimum amount of energy that particles must have to react

Question 8

Reaction profiles

Answer 8

Can be used to show the relative energies of reactants and products, the activation energy and the overall energy change of a reaction

Question 9

Reaction profile for endothermic reactions

Answer 9

Check chegg

Question 10

Reaction profile for exothermic reactions

Answer 10

Check chegg

Question 11

What happens during a chemical reaction (2)

Answer 11

• Energy must be supplied to break bonds in the reactants

* Energy is released when bonds in the products are formed

Question 12

What is the overall change of reaction

Answer 12

Is the difference between the sum of energy needed to break bonds in the reactants and the sum of the energy released when bonds in the products are formed

Question 13

Energy change in exothermic reactions

Answer 13

The energy released from forming new bonds is greater than the energy needed to break existing bonds

Question 14

Energy change in endothermic reactions

Answer 14

The energy needed to break existing bonds is greater than the energy released from forming new bonds

Question 15

How to calculate the energy transferred in chemical reactions using bond energies supplied?

Answer 15

All of the energy needed to break bonds in the reactants - the energy released when new bonds are formed in the products