energy changes c5

Question 1

example of exothermic reaction

Answer 1

wood burning

Question 2

what happens in an exothermic reaction

Answer 2

transfer energy into the surroundings

Question 3

what is important about the energy profile of exothermic reactions

Answer 3

the reactants have more energy than the products

Question 4

how do you find the energy transferred to surroundings in the energy profile of exothermic reactions

Answer 4

the difference between the energy of reactants and the energy of products

Question 5

what are 2 uses of exothermic reactions

Answer 5

hand warmers
self heating cans eg. for food or drink

Question 6

what happens in an endothermic reaction

Answer 6

take in energy from surroundings

Question 7

example of endothermic reaction

Answer 7

thermal decomposition

Question 8

what is important about the energy profile of endothermic reactions

Answer 8

the products have more energy than the reactants

Question 9

where is the activation energy on an energy profile

Answer 9

from the reactants to the peak of the curve

Question 10

what does the energy value of a chemical bond tell us

Answer 10

the amount of energy needed to break that bond

Question 11

how do we work out the energy needed to break chemical bond

Answer 11

add each part of energy needed up then take it away from the amount needed to form the new bonds

Question 12

what type of reaction is breaking bonds

Answer 12

endothermic

Question 13

what type of reaction is making bonds

Answer 13

exothermic

Question 14

what is an electrolyte

Answer 14

a solution that can conduct electricity

Question 15

key points about cells

Answer 15

• can only produce electricity for a short amount of time - eventually chemicals will run out and cell will stop working
• only work if we use metals with different conductivities

Question 16

if the reactivity of metals is greater what happens to the cell

Answer 16

the potential difference is greater

Question 17

difference between a battery and a cell

Answer 17

a battery is two or more cells connected in series to produce a greater voltage

Question 18

why can rechargeable batteries recharge

Answer 18

we can reverse the reaction when an electrical current is applied

Question 19

how do cells work

Answer 19

use a chemical reaction to produce electricity

Question 20

what is the half equation for the negative electrode in a fuel cell

Answer 20

2H(2) –> 4H(+) + 4e-

Question 21

what is the half equation for the positive electrode in a fuel cell

Answer 21

O2 + 4H(+) + 4e –> 2H(2)O

Question 22

what is the equations for a fuel cell

Answer 22

2H(2) + O(2) –> 2H(2)O

Question 23

what are the advantages of a hydrogen fuel cell

Answer 23

• produce electricity for as long as you provide hydrogen
• don’t get less efficient
• source of drinking water

Question 24

problems with hydrogen fuel cells

Answer 24

• hydrogen is an explosive gas
• produce relatively low potential difference so several needed together