C5 - Exothermic and Endothermic Reactions

Question 1

Law of conservation of Energy

Answer 1

Energy cannot be created or destroyed, only transferred

Question 2

Exothermic

Answer 2

A reaction which transfers energy to the surroundings (can be shown through rise of temperature)

Question 3

Examples of exothermic reactions

Answer 3

Combustion, neutralisation, oxidation

Question 4

Endothermic

Answer 4

A reaction which takes in energy from surroundings (shown by fall in temperature)

Question 5

Examples of endothermic reactions

Answer 5

Thermal decomposition

Question 6

How can you measure the amount of energy released by a chemical reaction?

Answer 6

By taking the temperature of the regents, mixing them in a polystyrene cup and measuring the temperature pf the solution at the end of the reaction

Question 7

What is the biggest problem when using temperature to measure the energy released in a reaction?

Answer 7

A lot of heat is lost to the surroundings

Question 8

How can you reduce the heat loss to the surroundings?

Answer 8

Using a polystyrene cup and placing it in a beaker of cotton wool to five more insulation, and putting a lid on the cup to reduce energy lost by evaporation (this method works for neutralisation)

Question 9

What other variables could you measure apart from the energy change?

Answer 9

The mass or concentration of the reactants used

Question 10

Exothermic reaction graph

Answer 10

• Products are at a lower energy than the reactants, the difference in height represents the overall energy change in the reaction per mole
• Activation energy is the initial rise in energy (which represents the energy needed to start the reaction)
• The activation energy is the minimum amount of energy the reactants need to collide with each other and react. The greater the activation energy, the more energy needed to start the reaction

Question 11

Endothermic reaction graph

Answer 11

• Products are at a higher energy than the reactants

- Difference in height represents the overall energy change during the reaction per mole

Question 12

What happens to the bonds in a chemical reaction?

Answer 12

• Old bonds are broken and new bonds are formed
• Endothermic reaction to break existing bonds
• Exothermic reaction is released when new bonds are formed
• Energy required to break bonds is greater than the energy released by forming them

Question 13

Every chemical bond has a particular … … associated with it

Answer 13

Bond energy (which varies slightly depending on the compound the bond occurs in)

Question 14

How to calculate the overall energy change for a reaction change?

Answer 14

Overall energy change is the sum of the energies needed to break bonds in the reactants minus the energy released when the new bonds are formed in the products