C7 - Energy Changes

Question 1

Exothermic

Answer 1

-transfers energy to surroundings
-increase temp of surroundings
-more energy in reactants than in products

Question 2

Exothermic eg

Answer 2

-combustion
-neutralisation

Question 3

Endothermic

Answer 3

–take in energy from surroundings
-drop in temp of surroundings
-more energy in products than in reactants

Question 4

Endothermic eg

Answer 4

thermal decomposition

Question 5

Hand warmers - disposable

Answer 5

-exothermic
-oxidation of iron

Question 6

Hand warmers - reusable

Answer 6

-place pack into boiling water to re dissolve crystals

Question 7

Self heating can

Answer 7

-calcium oxide + water —> calcium hydroxide
-exothermic

Question 8

Cold packs

Answer 8

-endothermic
-ammonium nitrate + water
-pack is compressed + seal is broken
-reaction occurs
-non reusable

Question 9

activation energy

Answer 9

minimum energy needed for colliding particles of reactants to have enough energy to cause a reaction

Question 10

Less energy of particle collisions causes

Answer 10

-bounce off each other
-do not react

Question 11

Exothermic reaction profile

Answer 11

-high reactants at the start
-low products at the end

Question 12

Endothermic reaction profiles

Answer 12

-low reactants at the start
-high products at the end

Question 13

Breaking bonds

Answer 13

-endothermic
-energy is needed to overcome bonds from surroundings

Question 14

Making bonds

Answer 14

-exothermic
-energy is transferred to surroundings

Question 15

Exothermic bond energy calculations

Answer 15

-more energy needed to break bonds in reactants

Question 16

Endothermic bond energy calculations

Answer 16

-more energy needed to form bonds in products

Question 17

bond energy

Answer 17

energy needed to break the bond between 2 atoms

Question 18

bond energy units

Answer 18

kJ/mol

Question 19

overall energy change for exothermic

Answer 19

-negative value

Question 20

overall energy change for endothermic

Answer 20

• positive value

Question 21

simple electrical cells

Answer 21

-2 metals dipped in salt solution
-connected by wire

Question 22

simple electrical cells - electrons

Answer 22

more reactive metal donates electrons to the less reactive metal

Question 23

the greater the difference in reactivity between the 2 metals

Answer 23

the higher the voltage produced by the cell is

Question 24

current

Answer 24

flow of electrons

Question 25

re chargeable batteries process

Answer 25

-battery connected to power supply -reverses reactions that occurs at each electrode -regenerates original reactants

Question 26

hydrogen powered vehicles

Answer 26

hydrogen burns well

Question 27

pros of h2

Answer 27

-not needed to be electrically recharged -no pollutants -range of sizes for range of use

Question 28

cons of using h2 fuel

Answer 28

-highly flammable -produced by using fossil fuels -difficult to store

Question 29

making hydrogen cons

Answer 29

- via electrolysis -requires electricity from fossil fuels -produces co2 -uses finite resources

Question 30

fuel cells

Answer 30

-oxidises h2 -fed w H2 + O2 to make water -energy supplies vehicle -but constant supply of H2 is needed

Question 31

Reaction at cathode process

Answer 31

-H2 to cathode as fuel -diffuses through graphite electrodes -sources electrons to an external circuit -

Question 32

Reaction at anode

Answer 32

-o2 to anode -diffuses through graphite electrodes -reacts to form OH ions -accepts ions from external cicuit -