Energy Changes

Question 1

What is an exothermic reaction?

Answer 1

A reaction that causes a rise in temperature to surroundings- it releases energy

Question 2

What is an endothermic reaction?

Answer 2

A reaction that causes a decrease in temperature in the surroundings-it takes in energy

Question 3

What is activation energy?

Answer 3

The minimum amount of energy that particles must have to take place

Question 4

How can we measure the amount of energy produced in a chemical reaction in solution?

Answer 4

By mixing the reactants in an insulated container. This enables heat that would be lost to surrounding to be measured.

Question 5

Bond breaking

Answer 5

Endothermic

Energy must be supplied to break existing bonds

Question 6

What happens in a chemical reaction?

Answer 6

Atoms are rearranged as old bonds are broken and new bonds are formed

Question 7

Bond forming

Answer 7

Exothermic

Energy is released when new binds are formed

Question 8

How can we measure the amount of energy produced in a chemical reaction in solution?

Answer 8

By mixing the reactants in an insulated container. This enables heat that would be lost to surrounding to be measured.

Question 9

How do cells release energy?

Answer 9

The chemical reactions between the electrodes and the electrolyte set up a charge difference between the electrodes
If the electrodes are then connected by a wire, the charge is able to flow and electricity is produced

Question 10

How Can a Simple cell be made?

Answer 10

By placing two different metals into a beaker containing an electrolyte

Question 11

Electrolyte

Answer 11

Liquid that contains ions which react with the electrodes

Question 12

Anode

Answer 12

Negative

Question 13

Cathode

Answer 13

Positive

Question 14

Name 2 everyday uses of exothermic reactions

Answer 14

> some hand warmers use the exothermic oxidation of iron in air
some self heating cans of hot chocolate or coffee rely on exothermic reactions between the chemicals in their bases

Question 15

Give an everyday use of endothermic reactions:

Answer 15

Sports injury pack

Question 16

What are reaction profiles?

Answer 16

diagrams that show the relative energies of reactants and products in a reaction and how the energy changes over the course of the reaction

Question 17

What can you use to accurately calculate the overall energy change of a reaction?

Answer 17

Bond energies

Question 18

Why are the two electrodes in an electrochemical cell usually metals?

Answer 18

They need to conduct electricity

Question 19

Why will the type of electrodes used in an electrochemical cell affect the voltage of the cell?

Answer 19

different electrodes react differently with the same electrolyte which is what produced the charge difference, or voltage, of the cell

Question 20

How is a battery formed?

Answer 20

connecting two or more cells together in series - the voltages of each cell are combined

Question 21

Non rechargeable batteries

Answer 21

batteries which contain cells which use irreversible reactions - once one of the reactants is completely used up, the battery doesn’t produce any more charge

Question 22

Rechargeable batteries

Answer 22

batteries where the reaction in the cells can be reversed by connecting it to an external electric current

Question 23

What is a fuel cell?

Answer 23

an electrical cell that is provided with fuel and oxygen and uses the energy from the reaction between them to efficiently produce electrical energy

Question 24

How is a pd set up in a fuel cell?

Answer 24

when the fuel enters the cell it oxidises and sets up a pd

Question 25

Give one important example of a fuel cell:

Answer 25

Hydrogen-oxygen fuel cell

Question 26

What does a hydrogen-oxygen fuel cell do?

Answer 26

combines hydrogen and oxygen to produce clean water and release energy

Question 27

What is the electrolyte and electrodes in a hydrogen-oxygen fuel cell?

Answer 27

electrolyte - potassium hydroxide solution

electrodes - porous carbon with a catalyst

Question 28

Where do the gases in a hydrogen-oxygen fuel cell go?

Answer 28

hydrogen goes into the anode compartment

oxygen goes into the cathode compartment

Question 29

What happens to hydrogen at the negative electrode?

Answer 29

it oxidises - it loses electrons to produce H+ ions

H2 –> 2H+ + 2e-

Question 30

What happens to the H+ ions in the electrolyte in a hydrogen-oxygen fuel cell?

Answer 30

They move towards the cathode

Question 31

What happens to oxygen at the cathode?

Answer 31

reduction - oxygen gains electrons and reacts with H+ ions from the electrolyte to make water
O2 + 4H+ + 4e- –> 2H2O

Question 32

What do hydrogen-oxygen fuel cells produce?

Answer 32

Water and heat

Question 33

What are half equations?

Answer 33

equations which show how electrons are transferred during reactions

Question 34

4 advantages of hydrogen-oxygen fuel cells in cars over batteries

Answer 34

> fuel cells’ only by-products are water and heat batteries don’t produce many pollutants either but are more polluting to dispose of due to the highly toxic metal compounds they are made from

> batteries are rechargeable but the number of times they can be recharged is still limited

> batteries are more expensive to make than fuel cells

> batteries store less energy and would need to be charged more often