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gcse science > Science - Chemistry - Energy Changes - C5 > Flashcards

Science - Chemistry - Energy Changes - C5 Flashcards

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1
Q

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

A

the surroundings

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2
Q

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

A

the surroundings

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3
Q

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

A

by heating

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4
Q

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

A

it will increase

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5
Q

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

A

it will decrease

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6
Q

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

A

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

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7
Q

what is an exothermic reaction ?

A

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

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8
Q

how is an exothermic reaction shown ?

A

by a temperature increase in the reactions

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9
Q

give an example of an exothermic reaction

A

combustion - burning fuels

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10
Q

what is an everyday use of an exothermic reaction ?

A
  • hand warmers use exothermic reactions
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11
Q

what is an endothermic reaction ?

A

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

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12
Q

how is an endothermic reaction shown ?

A

a decrease in temperature in the surroundings

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13
Q

what is an example of an endothermic reaction ?

A

photosynthesis

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14
Q

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

A

exothermic

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15
Q

what is an everyday use of an endothermic reaction ?

A

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

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16
Q

how can you compare how energy transfer changes ?

A

by measuring the temperature change of a reaction under different conditions

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17
Q

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

A

the temperature change of that reaction

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18
Q

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

A
  • 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
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19
Q

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

A

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

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20
Q

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

A

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

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21
Q

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

A

reactions of solids with liquids
reactions where you mix 2 solutions

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22
Q

how can you vary the energy transfer of reactions experiment ?

A
  • 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
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23
Q

if the reaction is exothermic, the bigger the

A

temperature of the solution will increase

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24
Q

the more energy is released, the

A

bigger the increase in temperature will be

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25
Q

if the reaction is endothermic the energy will be

A

absorbed and the temperature of the solution will decrease

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26
Q

the more energy absorbed, the bigger the

A

the decrease in temperature will be

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27
Q

what is energy measured in ?

A

joules

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28
Q

what are large energy values given in ?

A

kilojoules

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29
Q

how many joules are there in a kilojoule ?

A

1000

30
Q

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

A

how much a reactant is used

31
Q

what is energy transfer usually measured in ?

A

kilojoules per mole of reactant

32
Q

why is energy transferred in chemical reactions ?

A

because old bonds are broken and new bonds are formed

33
Q

what type of process is breaking a bond ?

A

an endothermic process

34
Q

why is breaking bonds an endothermic process ?

A

energy must be supplied to break existing bonds

35
Q

what type of process is making a bond ?

A

exothermic

36
Q

why is making a bond an exothermic process ?

A

energy is released when new bonds are formed

37
Q

what does a reaction being exothermic or endothermic depend on ?

A
  • 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
38
Q

what happens with energy and bonds in an exothermic reaction ?

A
  • 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
39
Q

what happens with energy and bonds in an endothermic reaction ?

A
  • 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
40
Q

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

A

each chemical bond has a particular bond energy associated with it

41
Q

what formula is used to work out the overall charge ?

A

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

42
Q

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

A

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

43
Q

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

A

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

44
Q

what is a cell ?

A

a system that contains chemicals which react and produce electricity

45
Q

what does a cell contain ?

A

2 different electrodes in contact with an electrolyte

46
Q

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

A

conduct electricity

47
Q

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

A

metals

48
Q

what is an electrolyte ?

A

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

49
Q

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

A

set up a charge difference between the electrodes

50
Q

how is electricity produced in a circuit ?

A

electrodes are connected by a wire then charge can flow

51
Q

what is the charge difference ?

A

the voltage of the cell

52
Q

what causes charge difference ?

A

different metals react differently with the same electrolyte

53
Q

the bigger the difference in reactivity of electrodes, the

A

bigger the voltage of the cell

54
Q

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 ?

A

0

55
Q

what does the voltage of the cell depend on ?

A

the concentration of ions in the electrolyte

56
Q

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

A

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

57
Q

what is a battery ?

A

2 or more cells connected together

58
Q

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

A

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

59
Q

how are some cells non - rechargeable ?

A

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

60
Q

how does a rechargeable cell work ?

A

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

61
Q

what is a fuel cell ?

A

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

62
Q

how do fuel cells work ?

A
  • 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
63
Q

what is a hydrogen - oxygen fuel cell ?

A

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

64
Q

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

A

potassium hydroxide

65
Q

what are the electrodes in hydrogen - oxygen fuel cells ?

A

porous carbon with a catalyst

66
Q

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

A

hydrogen loses the electrons to produce H+ ions - oxidation

67
Q

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

A

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

68
Q

what type of reaction is the hydrogen-fuel cell ?

A

a redox reaction where hydrogen and oxygen react to make water

69
Q

what are advantages to hydrogen fuel cells and batteries ?

A
  • don’t produce as much pollution
  • batteries are rechargeable
  • batteries store less energy than fuel cells
70
Q

what are disadvantages of hydrogen fuel cells ?

A
  • 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

gcse science (27 decks)

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