Energy Changes

Question 1

Activation energy

Answer 1

the minimum amount of energy required for a reaction to take place

Question 2

Exothermic reaction

Answer 2

A reaction where heat is given out to the surroundings, resulting in a temperature increase

Question 3

Endothermic reaction

Answer 3

A reaction where heat is taken in. This causes the temperature of the surroundings to decrease

Question 4

Examples of exothermic reactions (5)

Answer 4

• combustion: reaction of a fuel with oxygen releasing heat energy and at least one oxide
• oxidation: formation of hydrated iron (iii) oxide (rust)
• Neutralisation
• Displacement
• Rusting

Question 5

Examples of endothermic reactions (4)

Answer 5

• Thermal decomposition (Break down of a substance using heat)
• Photosynthesis (Green plants use sunlight to convert carbon dioxide and water into glucose and oxygen)
• Electrolysis
• Dehydration of hydrated salts

Question 6

Bond making=

Answer 6

Exothermic

Question 7

Bond breaking =

Answer 7

Endothermic

Question 8

What type of energy change value does an exothermic reaction have?

Answer 8

Negative, because energy is lost from the reaction

Question 9

What type of energy change value does an endothermic reaction have?

Answer 9

• Positive, because energy has been added to the reaction

Question 10

The overall energy change can be calculated…

Answer 10

From the difference between the energy put in to break the bonds in the reactants and the energy released when new bonds are formed in the products

Question 11

Energy change equation

Answer 11

Energy change = (energy taken in to break bonds in reactants) - (energy released when new bonds are formed in the products)

Question 12

Bond energy

Answer 12

The amount of energy required to break one mole of a specific covalent bond. The higher the bond energy the stronger the bond

Question 13

Conclusion from working out a reaction has negative energy change

Answer 13

The reaction is exothermic as the energy change is negative
This means that more energy is released in making new bonds in the product, HCl, than is taken in to break bonds in the reactants H2 and Cl2

Question 14

Reaction profile definition

Answer 14

A reaction profile for a chemical reaction shows how the energy of the chemicals changes as the reaction proceeds

Question 15

Describe the exothermic reaction profile (3)

Answer 15

• In an exothermic reaction, chemical energy in the reactants is converted into heat energy, which is released
• This means that the chemical energy going from reactants to products has decreased
• Reactants have more energy than the products

Question 16

Describe an endothermic reaction profile (3)

Answer 16

• In an endothermic reaction, heat energy taken in from the surroundings is converted into chemical energy in the products
• This means that the chemical energy going from reactants to products has increased
• The reactants have less energy than the products

Question 17

What is the activation energy on a reaction profile ?

Answer 17

The energy difference between the energy of the reactants and the top of the pathway is the activation energy

Question 18

Catalyst effect on reaction profiles

Answer 18

A catalyst works by providing an alternative reaction pathway of lower activation energy as it lowers the activation energy

Question 19

What do all chemicals possess?

Answer 19

Internal energy in their bonds

Question 20

What does a higher bond energy value mean in bond energies?

Answer 20

A higher bond energy value means a stronger covalent bond