energy changes

Question 1

what is an exothermic reaction

Answer 1

when energy is transferred to the surroundings in a chemical reaction

Question 2

give examples of exothermic reactions

Answer 2

• combustion
• oxidation
• neutralisation

Question 3

what is an endothermic reaction

Answer 3

chemical reactions that take heat energy from the surroundings

Question 4

give an example of an endothermic reaction

Answer 4

• thermal decomposition

Question 5

what is activation energy

Answer 5

the minimum amount of energy the reactant particles need in order to collide with each other and react

Question 6

what is bond energy

Answer 6

the amount of energy required to break one mole of a particular covalent bond

Question 7

is bond breaking endothermic or exothermic

Answer 7

endothermic

Question 8

is bond forming exothermic or endothermic

Answer 8

exothermic

Question 9

how do you calculate the total energy of the overall reaction

Answer 9

energy required to break bonds - energy released by forming bonds

Question 10

what is a fuel cell

Answer 10

a type of electrochemical cell

- converts energy between chemical and electrical

Question 11

what is the most common type of fuel cell

Answer 11

hydrogen-oxygen fuel cell

Question 12

what is the set up of a fuel cell

Answer 12

• an electrolyte in the centre
• electrodes on either side which are connected by a wire
• anode and cathode compartment on opposite sides

Question 13

what is the positive electrode in a fuel cell

Answer 13

cathode

Question 14

what is the negative electrode in a fuel cell

Answer 14

anode

Question 15

what are electrodes made out of in a fuel cell

Answer 15

porous carbon that contain a catalyst

Question 16

what happens to the hydrogen in a fuel cell

Answer 16

it is oxidised at the anode to form H+ ions

Question 17

what happens at the cathode in a fuel cell

Answer 17

the positive hydrogen ions react with the oxygen to produce water

Question 18

how do fuel cells generate electricity

Answer 18

hydrogen loses electrons which sets up a potential difference across the cell

Question 19

what are the advantages of hydrogen-oxygen fuel cells

Answer 19

• only require hydrogen and oxygen
• don’t produce any carbon dioxide
• last longer than batteries
• less polluting to dispose of

Question 20

what are the disadvantages of hydrogen-oxygen fuel cells

Answer 20

• hydrogen is a gas which makes it harder to store
• explosive when mixed with air
• storage is dangerous
• making the hydrogen fuel requires energy