Energy changes

Question 1

What is an exothermic reaction

Answer 1

when the chemicals in the reaction release energy into the surroundings so the temperature increases

Question 2

Give an example of an exothermic reaction

Answer 2

a combustion reaction such as methane burning in air

Question 3

What is an endothermic reaction?

Answer 3

when the chemicals take thermal energy from the surroundings so the temperature decreases

Question 4

Give an example of an endothermic reaction

Answer 4

a decomposition reaction such as metal carbonates decomposing into metal oxides and carbon dioxide

Question 5

How can you tell whether something is exothermic or endothermic from a reaction profile?

Answer 5

If the energy level of the reactants is above the products it is exothermic - has given out energy
If the energy level of the reactants is below the products it is endothermic - has taken in energy

Question 6

What is bond energy?

Answer 6

the amount of energy needed to break a bond
OR
the amount of energy released when bonds are made

Question 7

Describe an exothermic reaction in terms of bond energy

Answer 7

More energy is released making new bonds than is needed to break bonds

Question 8

Describe an endothermic reaction in terms of bond energy

Answer 8

More energy is released breaking bonds than is needed to make new bonds

Question 9

How can you work out if a reaction is endo or exothermic given the bond energies

Answer 9

1. Add together the bond energies of the reactants and subtract them from the products
   BE CAREFUL TO CHECK THE NUMBER OF MOLES OF EACH!
2. If the bonds broken in the reactants is higher than those made in the products it is endothermic,
3. If the bonds broken in the reactants is lower than those made in the products it is exothermic,