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Paper1- Chemistry > Topic 5 - Energy Changes > Flashcards

Topic 5 - Energy Changes Flashcards

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1
Q

why should you use a polystyrene cup and lid?(exo/endo required practical)

A

reduces heat energy lost to surroundings as it provides more insulation and lid reduces energy lost by evaporation

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2
Q

what is the dependant variable for the temperature change RP

A

temperature

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3
Q

what is the control variable for the temperature change RP

A

volume of acid

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4
Q

what is the independent variable for the temperature change RP

A

volume of odium hydroxide

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5
Q

why does the graph start to decrease at a certain volume (RP temperature change)

A

at a certain volume, the max temp decreases as sodium is in excess and cant react with enough HCl

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6
Q

what is the method to find the temperature change for exo and endo reactions RP

A
  1. measure 30 cm^3 of dilute hydrochloric acid using a measuring cylinder
  2. pour the acid in a polystyrene up and place it in a beaker( stops cup from falling)
  3. use a thermometer to measure temperature of acid- record in table
  4. measure 5 cm^3 of sodium hydroxide with a measuring cylinder and pour it into the polystyrene cup
  5. fit a plastic lid on cup and place thermometer through the hole- the bulb of thermometer must be in solution
  6. use thermometer to gently stir solution
  7. when temperature on thermometer stops changing, record the highest temp in the table
  8. rinse out cup and repeat whole experiment increasing sodium- by 5cm^3 each time until reach 40cm^3
  9. repeat whole experiment twice so you have sets of results and calculate mean
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7
Q

what is a fuel cell

A

an electrical cell supplied with an external source of fuel and oxygen

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8
Q

what happens to the fuel in the fuel cell

A

the fuel is oxidised electrochemically within the fuel cell to produce a potential difference

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9
Q

what is the equation for the reaction in the hydrogen fuel cell

A

the hydrogen fuel cell involves the oxidation of hydrogen to produce water
hydrogen + oxygen –> water + electricl energy

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10
Q

what is bad about using fuel cells

A

they are difficult to store

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11
Q

what is good about fuel cell vehicles

A

they don’t produce as many pollutants(greenhouse gases etc)
the only product is water an heat

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12
Q

what is the problem with electric vehicles

A
  • the batteries are more polluting to dispose of than fuel cells as they are made from highly toxic metal compounds
  • limit to how much they can be recharged
  • more expensive than fuel cells
  • store less energy so need to be recharged more often (time consuming)
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13
Q

what happens in a hydrogen fuel cell

A
  • hydrogen goes into the anode(-)
  • oxygen goes into the cathode (+)
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14
Q

what is formed at the anode(-) in a hydrogen fuel cell

A

hydrogen loses electrons to produce H+ ions (oxidation)

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15
Q

what is formed at the cathode(-) in a hydrogen fuel cell

A

oxygen gains electrons, and reacts with H+ to make water (reducation)

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16
Q

what is the electric current in a hydrogen fuel cell

A

the elctrons flow through an external circuit from the anode to the cathode this is the electric current

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17
Q

what is the half equation for the reaction at the anode in a hydrogen fuel cell

A

H2 –> 2H+ + 2e-

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18
Q

what is the half equation for the reaction at the cathode in a hydrogen fuel cell

A

O2 + 4H+ + 4e- —> 2H2O

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19
Q

what is a battery

A

formed by connecting 2 or more cells in series to provide a greater voltage

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20
Q

what are non rechargeable cells and batteries

A

made up of cells which use irreversible reactions

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21
Q

what happens to the reaction in a non rechargeable cell and battery when one of the reactants is used up

A

reaction stops and dont produce any more charge and must be replaced

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22
Q

what is an example of a non rechargeable cell and battery

A

alkaline batteries

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23
Q

what are rechargeable cells and batteries

A

can be recharged because the reactions are reversed when an external electrical current is supplied

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24
Q

what do cells contain

A

chemicals which react to produce electricity

25
Q

what is an electrochemical cell

A

a basic system made up of 2 different electrodes in contact with an electrolyte

26
Q

what are the electrodes made of

A

must be able to conduct electricity so are metals

27
Q

what does the difference in reactivity between electrodes mean

A

the greater the difference in reactivity, the greater the voltage

28
Q

what is the electrolyte

A

a liquid that contains ions which reacts with the electrodes

29
Q

what does the chemical reaction between electrodes and the electrolyte set up

A

a charge difference between the electrodes

30
Q

when is the charge in the electrodes able to flow

A

once the electrodes are connected by wire the charge is able to flow and electricity is produced

31
Q

how can the electrolyte affect the size of the voltage

A

as different ions react differently

32
Q

what are bond energies

A

energy required to break a particular covalent bond between 2 non metal atoms

33
Q

how do you find the overall energy change of reaction

A

sum of energies needed to break bonds in reactants - energy released when new bonds are formed in products

34
Q

how much energy needed to break all bonds
H-C=C-H
[ [
H H

A

c-H x 4 = 413 x 4= 1652
c=c x1 = 612 x 1= 612
1652 + 612= 2264 kj/mol

35
Q

calculate the energy change for reaction

H-H-C-H-H + 2 O=O —> 2o-H-o + o=c=o

A

C-H x4 = 1652
O=O x2= 996
1652+996= 2648

0=H x 2x2= 1856
o=c x 2= 1610
1856+1610= 3466
2648-3466= -818 KJ/Mol

36
Q

what happens to bonds during chemical reactions

A

old bonds are broken and new bonds are formed

37
Q

what happens in an endothermic process (bonds)

A

energy must be supplied to break existing bonds

38
Q

what happens in an exothermic process (bonds)

A

energy is released when new bonds are formed

39
Q

what is the word to remember bonds making and breaking

A

Bendo Mex

40
Q

what does Bendo Mex stand for

A

bond Breaking is ENDOthermic, bond Making is EXOthermic

41
Q

in an exothermic reaction what happens to the energy when breaking and making bonds

A

energy released from forming new bonds is greater than the energy needed to break existing ones

42
Q

in an endothermic reaction what happens to the energy when breaking and making bonds

A

energy needed to break existing bonds is greater than the energy than the energy released from forming new bonds

43
Q

what happens to amount of energy in chemical reactions

A

it is conserved
energy before chemical reaction = energy after

44
Q

what happens if the products store less energy

A

the excess energy is transferred to the surroundings during the reaction

45
Q

what happens if the product store more energy than the original reactants

A

they must have taken the difference in energy from the surroundings during the reaction

46
Q

what is a catalyst

A

a chemical that speeds up the rate of reaction by providing a lower energy pathway

47
Q

what do reaction profiles show

A

show the relative energies of reactants and products in a reaction and how the energy changes in the reaction

48
Q

what does a reaction profile fore an exothermic reaction look like

A
  • the reactants are higher than the products
49
Q

what does a reaction profile fore an endothermic reaction look like

A

the products are higher than the reactants

50
Q

how do you find the overall energy change on a reaction profile

A

the height in between the line for the products and the line for reactants

51
Q

how do you find the activation energy on a reaction profile

A

the height from the reactant line to the very top of the curve

52
Q

what is the activation energy

A

the minimum energy needed to stat a reaction

53
Q

what happens when the activation energy is large

A

the greater the activation energy, the more energy needed to start the reaction

54
Q

what is an exothermic reaction

A

transfers energy to the surroundings so temperature of surroundings increases

55
Q

what is examples of exothermic reactions

A

combustion, oxidation, neutralisation

56
Q

what are everyday uses of exothermic reactions

A
  • hand warmers use exothermic oxidation of iron in air to release energy
  • self heating cans of coffee rely on exothermic reactions between chemicals in the bases
57
Q

what are endothermic reactions

A

takes energy from the surroundings so the temperature decreases

58
Q

what are examples of endothermic reactions

A
  • reactions between citric acid and sodium hydrogen carbonate
  • thermal decompositions
59
Q

what is an everyday use of endothermic reactions

A
  • used in some sport injury packs- the chemical reaction allows pack to become instantly cooler with no freezer

Paper1- Chemistry (4 decks)

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