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year 10 mock exam revision > chemistry topic 5 energy changes > Flashcards

chemistry topic 5 energy changes Flashcards

1
Q

whats an exothermic reaction ?

A

a reaction which transfers energy to the surroundings usually by heating. this is shown by a rise in temperature

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2
Q

what reactions are exothermic?

A

combustion, neutralisation and oxidisation

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3
Q

what everyday objects provide exothermic reaction?

A

hand warmers and self heating cans

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4
Q

what is an endothermic reaction?

A

one which takes in energy from the surrounding. this is shown by a fall in temperature

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5
Q

whats an example of an endothermic reaction?

A

thermal decomposition

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6
Q

what everyday objects provide an endothermic reaction?

A

sports injury packs

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7
Q

how can you measure energy transfer in a practical?

A

taking the temperature of reagents, putting them in a polystyrene cup, mixing them and then measuring the temperature at the end

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8
Q

what is the biggest problem when measuring energy transfer?

A

energy can be lost in the surroundings

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9
Q

how can you reduce energy loss when measuring energy transfer?

A

put a lid on the cup and put more insulation in the cup e.g. cotton wool

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10
Q

what is bond breaking ? exothermic or endothermic?

A

endothermic

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11
Q

why is bond breaking an endothermic reaction?

A

energy must be supplied to break existing bonds

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12
Q

what is bonds formed? endothermic or exothermic?

A

exothermic

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13
Q

why is bond formation an exothermic reaction?

A

energy is released when new bonds are formed

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14
Q

in exothermic reactions the energy released by forming bonds is ?

A

greater than the energy used to break them

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15
Q

in endothermic reactions the energy used to break the bonds is?

A

greater than the energy released by forming them

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16
Q

in an exothermic reaction profile where are the products compared to the reactants?

A

the products are at a lower energy than the reactants

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17
Q

in an exothermic reaction profile what does the difference between products and reactants mean?

A

the overall energy change in the reaction

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18
Q

in an exothermic reaction profile what does the first rise in the line represent?

A

the energy needed to break the old bonds and start the reaction

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19
Q

in an exothermic and endothermic reaction profile what is the first initial rise called?

A

the activation energy

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20
Q

in an exothermic and endothermic reaction profile what is the activation energy?

A

the minimum amount of energy the reactants need to collide with each other and react

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21
Q

in an endothermic reaction profile where are the products compared to the reactants?

A

the products are at a higher energy than the reactants

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22
Q

in an endothermic reaction profile, what does the overall energy change mean?

A

the overall energy taken in

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23
Q

what is the equation for overall energy change?

A

overall energy change= energy required to break bonds-energy released by forming bonds

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24
Q

when finding bond energies what do you do?

A

add up the energies of your products and reactants then take them away reactants - products

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25
Q

what is an electrcochemical cell?

A

a basic system made up of two electrodes in contact with an electrolyte

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26
Q

exothermic endothermic practical: what do you prepare in separate beakers?

A

25 cm cubed of hydrochloric acid (o.25 mol/dm3) and sodium hydroxide

27
Q

exothermic endothermic practical: what do you do with your beakers at the start?

A

place the beakers in a water bath set to 25 degrees until they are the same temperature

28
Q

exothermic endothermic practical: what do you do after the beakers are the same temperature?

A

add the HCl followed by the NAOH to a polystyrene cup with a lid

29
Q

exothermic endothermic practical: how often do you take the temperature and what do you record?

A

every 30 seconds and record highest temperature

30
Q

exothermic endothermic practical: what do you repeat the practical using?

A

0.5 mol/dm3 and 1 mol/dm3 of hydrochloric acid

31
Q

what must the two electrodes be able to do in an electrochemical cell?

A

conduct electricity

32
Q

what is the electrolyte in a electrochemical cell?

A

a liquid that contains ions which react with other electrodes

33
Q

what do the chemical reactions between the electrodes and the electrolyte set up in an electrochemical cell?

A

charge differences between the electrode

34
Q

if the electrochemical cell has electrodes connected by wire, what can charge do?

A

flow and electricity Is produced

35
Q

what can be connected to an electrochemical cell to measure volts?

A

voltmeter

36
Q

the bigger the difference in reactivity of the electrodes, the bigger the what?

A

voltage of the cell

37
Q

how will the electrolyte used affect the voltage?

A

different ions will react differently with the electrodes used

38
Q

how is a battery formed?

A

by connecting two or more cells together in series

39
Q

what kind of reaction happens in a non rechargeable battery?

A

irreversible one

40
Q

what happens over time to reacting particles in a non rechargeable cell?

A

the ions in the electrolyte and electrode get used up and turn into products for the reaction

41
Q

once the reactants are all used up in non rechargeable batteries what happens?

A

reaction cant happen and no electricity is produced as reaction cant be reversed

42
Q

how do rechargeable batteries work again?

A

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

43
Q

what is the chemical name for a non rechargeable battery?

A

alkaline battery

44
Q

what is a fuel cell?

A

an electrical cell supplied with fuel and oxygen- it uses energy from the reaction between them to produce electrical energy efficiently

45
Q

when fuel enters a fuel cell what happens?

A

it becomes oxidised and sets up a potential difference within the cell

46
Q

whats an example of a fuel cell?

A

hydrogen- oxygen fuel cell

47
Q

what happens in a hydrogen oxygen fuel cell?

A

it combines hydrogen and oxygen to produce nice clean water and energy

48
Q

how are hydrogen-oxygen fuel cells used in vehicles?

A

conventional fuels like petrol are finite and very polluting therefore vehicles use electrical energy to power them

49
Q

advantages of hydrogen-oxygen fuel cells: what don’t they produce?

A

many pollutants (carbon monoxide carbon dioxide etc)

50
Q

advantages of hydrogen-oxygen fuel cells: what are the only by-products of them?

A

water and heat

51
Q

advantages of hydrogen-oxygen fuel cells: electric vehicles car cells don’t produce many pollutants however what is it like to dispose of them ?

A

more polluting because they’re made from highly toxic metal compounds

52
Q

hydrogen-oxygen fuel cells: what is bad about the rechargeable electric batteries in cars?

A

theres a limit on how many times you can recharge them before they need replacing

53
Q

of hydrogen-oxygen fuel cells: what is the cost like of a rechargeable cell?

A

they are more expensive than fuel cells

54
Q

hydrogen-oxygen fuel cells: what don’t batteries store as much compared to fuel cells?

A

less energy- they need to be recharged more often

55
Q

in a hydrogen-oxygen fuel cell what is the electrolyte often?

A

potassium hydroxide

56
Q

where does hydrogen and oxygen go in a fuel cell?

A

hydrogen goes in the anode compartment and oxygen goes in the cathode comnpartment

57
Q

what happens at thenegative electrode in a fuel cell?

A

hydrogen loses electrons to produce H+ ions. this is oxidation

58
Q

where do the H+ ions move in a fuel cell?

A

they move to the cathode

59
Q

what happens at the positive electrode in a fuel cell?

A

oxygen gains electrons from the cathode and react with h+ ions to make water. this is reduction

60
Q

where do electrons flow in a fuel cell?

A

through an external circuit from the anode to cathpde (the electric current)

61
Q

what is the overall reaction for a hydrogen- oxygen fuel cell?

A

hydrogen + oxygen = water

62
Q

how is a fuel cell a redox reaction?

A

theres reduction at cathode and oxidation at anode

63
Q

when something is oxidised where are the electrons in the half equation?

A

last thing

64
Q

when something is reduced where are the electrons in the half equation?

A

before arrow

year 10 mock exam revision (26 decks)

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