C7

Question 1

Exothermic and endothermic reactions in terms of bonds?

Answer 1

Breaking bonds aBsorbs energy, forRming bonds Releases energy

Question 2

What is Activation energy?

Answer 2

minimum energy required for a reaction to take place

Question 3

What kind of reactions are neutralisation reactions?

Answer 3

exothermic

Question 4

RQ. What equipment do you need to investigate temperature changes?

Answer 4

poly(styrene) cup and thermometer

Question 5

RQ. Method for investigating temperature changes? safety?
improvements?

Answer 5

• Record initial temperatures of reactants
• mix reactants in cup
• record max/minimum temperatures reached
• Safety = goggles
• improvements= lid for cup, stirring to get even distribution of heat

Question 6

Uses of exothermic reactions? (2)

Answer 6

Chemical hand warmers, self-heating cans

Question 7

3 main endothermic reactions?

Answer 7

Photosynthesis, hydrogen carbonate + acid (sherbet), dissolving ammonium nitrate in water

Question 8

Equation for reaction in self-heating cans?

Answer 8

calcium oxide + water > calcium hydroxide

Question 9

Uses of endothermic reactions?

Answer 9

Chemical cold packs

Question 10

How do chemical cold packs work?

Answer 10

They contain ammonium nitrate and water, when ammonium nitrate dissolves, it absorbs energy from surroundings

Question 11

What is Bond energy?

Answer 11

Energy needed to break a bond between 2 atoms

Question 12

What units are bond energies measured in?

Answer 12

kJ/mol

Question 13

You can use bond energies to work out…

Answer 13

the energy change for most reactions

Question 14

When new bonds are formed between atoms….

Answer 14

energy is released

Question 15

Energy must be supplied to…

Answer 15

break chemical bonds

Question 16

What is an exothermic reaction?

Answer 16

One that gives out energy to the surroundings

Question 17

What is an endothermic reaction?

Answer 17

One that takes in energy from the surroundings

Question 18

In terms of energy, what happens when bonds are broken?

Answer 18

Energy is required (endothermic)

Question 19

In terms of energy, what happens when bonds are formed?

Answer 19

Energy is released (exothermic)

Question 20

How do you remember whether energy is released or required when bonds are being rearranged?

Answer 20

Bendy Mexicans:

B(endo)ROKEN
M(exo)ADE

Question 21

What does it mean if the energy of the products is lower than the reactants?

Answer 21

Energy has been released and the reaction is exothermic

Question 22

What does it mean if the energy of the products is higher than the reactants?

Answer 22

Energy has been taken in and the reaction is endothermic

Question 23

How does a catalyst increase the rate of reaction?

Answer 23

By lowering the activation energy

Question 24

READ ONLY:

How do you work out total energy change?

Answer 24

• total for breaking bonds: no. of bonds x breaking bond energy
• total for making bonds: no. of bonds x making bond energy
• total energy change: breaking bonds - making bonds

Question 25

What does it mean if you get a positive number when working out energy change?

Answer 25

The reaction is endothermic

Question 26

What does it mean if you get a negative number when working out energy change?

Answer 26

The reaction is exothermic

Question 27

In terms of energy change, what do exothermic and endothermic reactions always have?

Answer 27

• endothermic always have positive energy changes * exothermic always have negative

Question 28

How can a simple cell be made?

Answer 28

By connecting two different metals in contact with an electrolyte

Question 29

What do batteries consist of to provide a greater voltage?

Answer 29

Two or more cells connected

Question 30

What chemicals are cells made from?

Answer 30

• carbon rod with metal cathode • manganese oxide • ammonium chloride • zinc casting anode

Question 31

What is the electrolyte in a cell made of?

Answer 31

Ammonium chloride

Question 32

What is the anode made of in a cell?

Answer 32

Zinc casting

Question 33

What does the voltage produced by a cell depend on?

Answer 33

The type of metals making up the cathode and anode and electrolyte

Question 34

What happens when two metals are dipped in salt solution and joined by a wire?

Answer 34

The more reactive metal will donate electrons to the less reactive metal to form an electrical cell

Question 35

Which metal will lose their electrons in a simple electrical cell?

Answer 35

The more reactive metal

Question 36

What happens when there is a greater difference between reactivity of metals in a cell?

Answer 36

There will be a higher voltage produced

Question 37

Are alkaline batteries rechargeable?

Answer 37

No

Question 38

What happens when one of the reactants has been used up in non-rechargeable batteries?

Answer 38

The chemical reactions stop

Question 39

What happens to the chemical reactions in rechargeable batteries?

Answer 39

They are reversed using an external electrical current

Question 40

How do hydrogen fuel cells work?

Answer 40

• oxygen is supplied to the positive electrode and diffuses through the graphite to react to form hydroxide ions - accepting electrons from the external circuit • hydrogen is supplied to the negative electrode and diffuses through the graphite electrode and reacts with hydroxide ions to form water • overall charge left in fuel cell

Question 41

What hydrogen fuel cells offer an alternative to?

Answer 41

Fossil fuels and rechargeable cells and batteries

Question 42

Advantages of hydrogen fuel cells?

Answer 42

• don't need to be electrically recharged • no pollutants produced • can be a range of sizes for different uses • do not get less efficient as they run • can be a source of drinking water

Question 43

Disadvantages of hydrogen fuel cells?

Answer 43

• hydrogen is flammable and difficult to store • hydrogen is sometimes produced for the cell by non renewable sources • produce a relatively low voltage so several are needed together

Question 44

What are fuel cells useful as an energy source for aircraft?

Answer 44

• provide water • efficient • no moving parts • lightweight

Question 45

Half equation for the hydrogen supplied to a hydrogen fuel cell? (anode)

Answer 45

H2 -> 2H+ + 2e-

Question 46

Half equation for the oxygen supplied to a hydrogen fuel cell?

Answer 46

02 + 4H2+ 4e- > 2H20

Question 47

Equation for the two electrode reactions in a hydrogen fuel cell?

Answer 47

2H2 + 02 →> 2H20