Science - Chemistry - Energy Changes - C5

Question 1

if the products of a reaction store more energy than the original reactants, where was the energy transferred from ?

Answer 1

the surroundings

Question 2

if the products of a reaction stores less energy than the original reactants, where was the excess energy transferred to ?

Answer 2

the surroundings

Question 3

how is energy usually transferred between the reactants and the surroundings during a chemical reaction ?

Answer 3

by heating

Question 4

if energy is transferred to the surroundings, what will happen to the temperature of the surroundings ?

Answer 4

it will increase

Question 5

if energy is transferred from the surroundings, what will happen to the temperature of the surroundings ?

Answer 5

it will decrease

Question 6

why doesn’t the amount of energy in the reactants and surroundings change ?

Answer 6

the conservation of energy - energy can’t be created nor destroyed, only transferred

Question 7

what is an exothermic reaction ?

Answer 7

a reaction where energy is transferred from the reaction to the surroundings

Question 8

how is an exothermic reaction shown ?

Answer 8

by a temperature increase in the reactions

Question 9

give an example of an exothermic reaction

Answer 9

combustion - burning fuels

Question 10

what is an everyday use of an exothermic reaction ?

Answer 10

• hand warmers use exothermic reactions

Question 11

what is an endothermic reaction ?

Answer 11

a reaction where energy is taken in from the surroundings during a reaction

Question 12

how is an endothermic reaction shown ?

Answer 12

a decrease in temperature in the surroundings

Question 13

what is an example of an endothermic reaction ?

Answer 13

photosynthesis

Question 14

which type of reaction is more common - endothermic or exothermic ?

Answer 14

exothermic

Question 15

what is an everyday use of an endothermic reaction ?

Answer 15

a sports injury pack is a cold pack used to reduce swelling, they take in heat and the pack becomes cold

Question 16

how can you compare how energy transfer changes ?

Answer 16

by measuring the temperature change of a reaction under different conditions

Question 17

what is the amount of energy transferred during a reaction proportional to ?

Answer 17

the temperature change of that reaction

Question 18

describe the experiment on how to measure energy transfer of reactions ?

Answer 18

• take the temperature of the reactants, mixing everything together in a polystyrene cup
• measure the temperature
• seal the cup as much as possible, put cotton around the cup to insulate it and stop energy being lost to the surroundings
• measure the temperature at the end of the reaction

Question 19

what is the hardest thing when doing the experiment to measure energy transfer of reactions ?

Answer 19

the amount of energy that’s lost to the surroundings during the experiment

Question 20

why does a polystyrene cup help with the experiment energy transfer of reactions ?

Answer 20

it helps to insulate the reaction mixture more than a glass beaker

Question 21

what does the energy transfer of reactions experiment method work for ?

Answer 21

reactions of solids with liquids
reactions where you mix 2 solutions

Question 22

how can you vary the energy transfer of reactions experiment ?

Answer 22

• you can investigate the effect of changing the amount of reactant has on the energy transferred, so you can repeat the experiment with a different mass/ concentration

Question 23

if the reaction is exothermic, the bigger the

Answer 23

temperature of the solution will increase

Question 24

the more energy is released, the

Answer 24

bigger the increase in temperature will be

Question 25

if the reaction is endothermic the energy will be

Answer 25

absorbed and the temperature of the solution will decrease

Question 26

the more energy absorbed, the bigger the

Answer 26

the decrease in temperature will be

Question 27

what is energy measured in ?

Answer 27

joules

Question 28

what are large energy values given in ?

Answer 28

kilojoules

Question 29

how many joules are there in a kilojoule ?

Answer 29

1000

Question 30

what does the amount of energy released or absorbed depend on ?

Answer 30

how much a reactant is used

Question 31

what is energy transfer usually measured in ?

Answer 31

kilojoules per mole of reactant

Question 32

why is energy transferred in chemical reactions ?

Answer 32

because old bonds are broken and new bonds are formed

Question 33

what type of process is breaking a bond ?

Answer 33

an endothermic process

Question 34

why is breaking bonds an endothermic process ?

Answer 34

energy must be supplied to break existing bonds

Question 35

what type of process is making a bond ?

Answer 35

exothermic

Question 36

why is making a bond an exothermic process ?

Answer 36

energy is released when new bonds are formed

Question 37

what does a reaction being exothermic or endothermic depend on ?

Answer 37

* what bond breaking and what bond making is going on * whether the amount of energy is absorbed when the bonds in the reactants are broken is more or less * when the bonds in the products are made

Question 38

what happens with energy and bonds in an exothermic reaction ?

Answer 38

* the energy released in bond formation is greater than the energy used in breaking old bonds * the leftover energy is released into the surroundings and the temperature rises

Question 39

what happens with energy and bonds in an endothermic reaction ?

Answer 39

* the energy needed to break old bonds is greater than the energy released when new bonds are formed * the extra energy needed is absorbed from the surroundings and the temperature falls

Question 40

why do some bonds need more energy to break than others ?

Answer 40

each chemical bond has a particular bond energy associated with it

Question 41

what formula is used to work out the overall charge ?

Answer 41

energy change = energy of bond breaking - energy of bond making

Question 42

if the overall energy change is negative what does that show ?

Answer 42

more energy was released in bond making than used in bond breaking - exothermic

Question 43

if the overall energy change is positive what does that show ?

Answer 43

more energy was used in bond breaking than bond making - endothermic

Question 44

what is a cell ?

Answer 44

a system that contains chemicals which react and produce electricity

Question 45

what does a cell contain ?

Answer 45

2 different electrodes in contact with an electrolyte

Question 46

what do the 2 electrodes in a cell must be able to do ?

Answer 46

conduct electricity

Question 47

what are electrodes usually made of because they need to conduct electricity ?

Answer 47

metals

Question 48

what is an electrolyte ?

Answer 48

a liquid hat conducts electricity and contains ions which react with the electrodes

Question 49

what do the chemical reactions between the electrodes and the electrolyte do ?

Answer 49

set up a charge difference between the electrodes

Question 50

how is electricity produced in a circuit ?

Answer 50

electrodes are connected by a wire then charge can flow

Question 51

what is the charge difference ?

Answer 51

the voltage of the cell

Question 52

what causes charge difference ?

Answer 52

different metals react differently with the same electrolyte

Question 53

the bigger the difference in reactivity of electrodes, the

Answer 53

bigger the voltage of the cell

Question 54

if theres no difference in reactivity because the reactivity of the metals is the same or the same metal is used as an electrode, what will the voltage of the cell be ?

Answer 54

0

Question 55

what does the voltage of the cell depend on ?

Answer 55

the concentration of ions in the electrolyte

Question 56

why does the concentration of ions in the electrolyte affect the voltage of a cell ?

Answer 56

as the ions in the electrolyte react, their concentration will decrease, so will the voltage of the cell so the cell will drop to 0 and stop working

Question 57

what is a battery ?

Answer 57

2 or more cells connected together

Question 58

why is the voltage of the battery greater than any of the individual cells in the battery ?

Answer 58

the voltage of the battery is all the voltages of the cell added together

Question 59

how are some cells non - rechargeable ?

Answer 59

the chemical reactions that happen in the electrodes are irreversible because over time the reacting particles get used up and turn into the products of the reaction once any of the reactants are used up, the cell won't work

Question 60

how does a rechargeable cell work ?

Answer 60

the reaction can be reversed by connecting it to an external electric current

Question 61

what is a fuel cell ?

Answer 61

an electrical cell that's supplied with a fuel and oxygen and efficiently transfers the energy released by the reaction between them as electricity

Question 62

how do fuel cells work ?

Answer 62

- the fuel enters the cell at one side - it becomes oxidised and sets up a potential difference within a cell - potential difference powers the device that the fuel is connected to - oxygen enters the the cell at the other side, where it reacts to form water

Question 63

what is a hydrogen - oxygen fuel cell ?

Answer 63

the fuel cell is hydrogen which is oxidised when it combines with oxygen to produce water and releases energy

Question 64

what is the electrolyte a solution of in hydrogen - oxygen fuel cells ?

Answer 64

potassium hydroxide

Question 65

what are the electrodes in hydrogen - oxygen fuel cells ?

Answer 65

porous carbon with a catalyst

Question 66

what happens at the negative electrode during hydrogen-oxygen fuel cells ?

Answer 66

hydrogen loses the electrons to produce H+ ions - oxidation

Question 67

what happens at the positive electrode during hydrogen-oxygen fuel cells ?

Answer 67

oxygen gains electrons and reacts with H+ ions to make water - reduction

Question 68

what type of reaction is the hydrogen-fuel cell ?

Answer 68

a redox reaction where hydrogen and oxygen react to make water

Question 69

what are advantages to hydrogen fuel cells and batteries ?

Answer 69

- don't produce as much pollution - batteries are rechargeable - batteries store less energy than fuel cells

Question 70

what are disadvantages of hydrogen fuel cells ?

Answer 70

- hydrogen is a gas so takes up more space to store - batteries are or expensive than fuel cells - hydrogen is explosive when mixed with air so is more hard to store safely - hydrogen fuel is made from hydrocarbons or by electrolysis of water which uses electricity and this has to be generated somehow