Enthalpy Change In Endothermic And Exothermic Reactions

Question 1

What is an exothermic reaction

Answer 1

One that releases energy to its surroundings, meaning the energy released on bond formation in the products is greater than that absorbed through breaking bonds in the reactants

Question 2

What is an endothermic reaction

Answer 2

One that takes in energy from its surroundings meaning the energy needed to be absorbed to break bonds in the reactants is greater than the energy transferred to the surroundings as bonds are made in the products

Question 3

Does breaking bonds take in or release energy

Answer 3

Takes in energy

Question 4

Is breaking bonds exothermic or endothermic

Answer 4

Endothermic

Question 5

Does making bonds release or take in energy

Answer 5

Releases energy

Question 6

Is making bonds exothermic or endothermic

Answer 6

Exothermic

Question 7

Examples of exothermic reactions

Answer 7

Combustion and neutralisation

Question 8

Example of endothermic reaction

Answer 8

Photosynthesis

Question 9

What is enthalpy change and it’s unit

Answer 9

The thermal energy change at a stated temperature and pressure, units are kJmol-1

Question 10

What are standard conditions

Answer 10

101kPa and 298K

Question 11

What is the enthalpy change in exothermic reaction

Answer 11

Negative value as energy is lost to the surroundings

Question 12

What is the enthalpy change in endothermic reactions

Answer 12

Always a positive value as energy is gained by the system from the surroundings

Question 13

How to work out enthalpy change

Answer 13

Bond enthalpies of reactants - bond enthalpies of products

Question 14

Why are bond enthalpies averages

Answer 14

Because every single bond in a compound has a slightly different bond enthalpy, differ with the environment