C5: Energy Changes

Question 1

What change in temperature is associated with an exothermic reaction?

Answer 1

a temperature rise; they transfer thermal energy to the surroundings

Question 2

What change in temperature is associated with an endothermic reaction?

Answer 2

a temperature fall; heat energy is transferred from the surroundings to the chemicals

Question 3

What is the activation energy of a reaction?

Answer 3

the minimum amount of energy that the particles must have for a reaction to take place

Question 4

How can the energy changes in a reaction be shown?

Answer 4

an energy level diagram or a reaction profile

Question 5

In terms of energy, what happens in an exothermic reaction?

Answer 5

-energy is given out to the surroundings
-the products have less energy than the reactants

Question 6

In terms of energy, what happens in an endothermic reaction?

Answer 6

-energy is being taken from the surroundings
-the products have more energy than the reactants

Question 7

What is a catalyst?

Answer 7

they reduce the activation energy needed for a reaction; this increases the rate of reaction

Question 8

What sort of a reaction is breaking a chemical bond?

Answer 8

an endothermic reaction; it requires energy

Question 9

What sort of a reaction is forming a chemical bond?

Answer 9

an exothermic reaction; it releases energy

Question 10

If more energy is required to break bonds than is released when forming new ones, what sort of a reaction is it?

Answer 10

endothermic

Question 11

If more energy is released when forming new ones than is required when breaking them, what sort of reaction is it?

Answer 11

exothermic

Question 12

What is a cell?

Answer 12

contains chemicals that react together to release electricity

Question 13

How can a simple cell be made?

Answer 13

by placing two different metals into a beaker containing an electrolyte

Question 14

How are batteries made?

Answer 14

when two or more cells are connected together

Question 15

What is the voltage released by a cell dependent on?

Answer 15

type of electrode and electrolyte used

Question 16

Why do non-rechargeable batteries stop producing electricity?

Answer 16

one of the reactants has been used up

Question 17

What is a fuel cell?

Answer 17

a very efficient way of producing electrical energy in which a fuel is oxidised electrochemically to produce a potential difference or voltage

Question 18

What do most fuel cells use as a fuel?

Answer 18

hydrogen

Question 19

What happens inside a hydrogen fuel cell?

Answer 19

-hydrogen and oxygen are supplied to the fuel cell
-the fuel is oxidised to produce a potential difference
-overall, the hydrogen is oxidised to form water

Question 20

What are some advantages of fuel cells?

Answer 20

-hydrogen fuel cells produce water which is non-polluting
-they are lightweight and small
-they have no moving parts so are very unlikely to break down