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edexcel igcse chemistry > unit three: physical chemistry > Flashcards

unit three: physical chemistry Flashcards

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1
Q

what is the test for lithium

A

dip a nichrome wire in hydrochloric acid to clean it,,. pick up some of the crystals on the wire and hold them on the edge of a blue bunsen flame.

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2
Q

what is the observation when testing lithium

A

a bright red flame

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3
Q

what is the test for sodium

A

dip a nichrome wire in hydrochloric acid to clean it,,. pick up some of the crystals on the wire and hold them on the edge of a blue bunsen flame.

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4
Q

what is the observation when testing sodium

A

yellow flame

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5
Q

what is the test for potassium

A

dip a nichrome wire in hydrochloric acid to clean it,,. pick up some of the crystals on the wire and hold them on the edge of a blue bunsen flame.

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6
Q

what is the observation when testing calcium

A

orange-red flame

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7
Q

what is the test for calcium

A

dip a nichrome wire in hydrochloric acid to clean it,,. pick up some of the crystals on the wire and hold them on the edge of a blue bunsen flame.

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8
Q

what is the test for copper

A

dip a nichrome wire in hydrochloric acid to clean it,,. pick up some of the crystals on the wire and hold them on the edge of a blue bunsen flame.

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9
Q

what is the observation when testing copper

A

green flame

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10
Q

what is the test for aqueous copper

A

add aqueous sodium hydroxide a drop at a time to form a precipitate.

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11
Q

what is the observation when testing aqueous copper

A

blue precipitate

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12
Q

what is the test for aqueous iron (II)

A

add aqueous sodium hydroxide a drop at a time to form a precipitate.

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13
Q

what is the observation when testing aqueous iron (II)

A

green precipitate

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14
Q

what is the test for aqueous iron (III)

A

add aqueous sodium hydroxide a drop at a time to form a precipitate.

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15
Q

what is the observation when testing aqueous iron (III)

A

brown precipitate

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16
Q

how do you test for ammonia

A

add aqueous sodium hydroxide to the solid or solution under test and warm the mixture

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17
Q

what is the observation when testing for ammonia

A

a pungent-smelling gas is produced. the gas produced turns damp red litmus paper blue

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18
Q

what is the test for chlorine

A

to an aquous solution of the solid under test, add some dilute nitric acid followed by a few drops of silver nitrate solution.

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19
Q

what is the observation when testing for chlorine

A

white precipitate

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20
Q

what is the observation when testing for bromine

A

cream precipitate

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21
Q

what is the test for bromine

A

to an aquous solution of the solid under test, add some dilute nitric acid followed by a few drops of silver nitrate solution.

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22
Q

what is the test for iodine

A

to an aquous solution of the solid under test, add some dilute nitric acid followed by a few drops of silver nitrate.

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23
Q

what is the observation when testing for iodine

A

yellow precipitate

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24
Q

what is the test for sulphate

A

to an aqueous solution of the solid under test, add dilute hydrochloric acid followed by a few drops of barium chloride solution

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25
Q

what is the observation when testing for sulfate

A

white precipiate

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26
Q

what is the test for carbonate

A

to either the solid, or an aqueous solution of the solid under test add dilute hydrochloric (or nitric) acid.

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27
Q

what is the observation when testing for carbonate

A

bubbles of gas. the gas produced turns limewater milky.

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28
Q

Q =

A

m x c x Δt

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29
Q

ΔH =

A

Q / n

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30
Q

exothermic

A

energy is given out

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31
Q

endothermic

A

energy is taken in

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32
Q

example of an exothermic reaction

A

the reaction between sulfuric acid and magnesium

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33
Q

example of an endothermic reaction

A

the reaction between sodium hydrogen carbonate and citric acid

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34
Q

what is specific heat capaacity

A

the amount of heat needed to raise the temperature of a substance by 1 degree celsius

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35
Q

specific heat capacity of water

A

4.18 J/g/degree celsius

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36
Q

breaking bonds

A

needs energy

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37
Q

making bonds

A

releases energy

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38
Q

what does anhydrous mean

A

without water

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39
Q

if you heat blue copper sulfate crystals until they turn to a white powder and then and water to it again what happens

A

it turns blue again and is very warm.

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40
Q

what is the reversible reaction symbol

A

⇌

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41
Q

if you heat ammonium chloride what happens

A

the white crystals disappear from the bottom of the tube and reappear further up. it splits it into the colourless gasses ammonia and hydrogen chloride

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42
Q

the stronger the bond

A

the more energy is required to break it

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43
Q

what are bond energies measured in

A

kJ/mol

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44
Q

is breaking bonds endo or exothermic

A

it needs energy, so endothermic

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45
Q

is making bonds endo or exothermic

A

it releases energy so exothermic

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46
Q

which type of substance are bond energy calculations used for

A

covalent molecules

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47
Q

if the sign of the overall bond energy calculation is negative what does it mean

A

heat is given out as the bonds rearrange. the reaction is exothermic

48
Q

if the sign of the overall bond energy calculation is positive what does it mean

A

heat has been absorbed as the bonds rearrange, the reaction is endothermic

49
Q

what is a closed system

A

no substances are added to the reaction mixture and no substances escape from it. heat may be lost or absorbed.

50
Q

what is dynamic equilibrium

A

rate of forward reaction = rate of backward reaction

51
Q

what is the forward reaction

A

left to right

52
Q

what is the backward reaction

A

right to left

53
Q

when does the position of equilibrirum lie to one direction

A

if the reaction is at equilibrium but htere is more of the left substance than the right substance then the position of equilibrium lies to the left, and vice versa

54
Q

how would you change rate of reaction

A

change pressure
change temperatyre
add a catalyst (this has no effect on the position of equilibrium)

55
Q

exothermic changes apart from burning:

A

the reactions of metals with acids
neutralisation reactions
displacement reactions

56
Q

what is enthalpy change

A

the amount of heat energy taken in or given out in a chemical reaction

57
Q

enthalpy is the difference between

A

energy of the products and energy of the reactants

58
Q

does endothermic have a negative or positive enthalpy change

A

a positive because the reactants are absorbing heat

59
Q

does exothermic have a negative or positive enthalpy change

A

negative because the reactants are losing heat

60
Q

how do you make a substance decompose

A

heat it constantly

61
Q

what is specific heat capacity

A

the amount of heat needed to raise the temperature of 1 gram of substance by 1 degree

62
Q

is combustion a endothermic or exothermic reaction

A

exothermic reaction

63
Q

major errors in evaluation of experimental results for enthalpy changes

A

large amounts of heat loss

could be incomplete combustion

64
Q

how can you tell if an alcohol is combusting completely

A

the flame should be blue and carbon dioxide should be produced instead of carbon

65
Q

how can you tell if an alochol is combusting incompletely

A

the flame of the wick is often yellow orange and carbon is produced.

66
Q

what does (in) excess mean

A

more than enough of a reactant is present to ensure all of the other reactant(s) react

67
Q

breaking bonds is

A

endothermic

68
Q

making bonds is

A

exothermic

69
Q

what are bond energies measured in

A

kJ/mol

70
Q

bond energy definition

A

the amount of energy needed to break 1 mole of covalent bonds in gaseous molecules

71
Q

what does a sealed container/closed system mean

A

no substances are added to the reaction mixture and no substances escape from it.
heat can be given off or absorbed.

72
Q

define dynamic equilibrium

A

the total amounts or concentrations of the reactants and products are now constant.

73
Q

give features of dynamic equilibrium (5)

A

rate of forward reaction = rate of backward reaction
closed system
the concentrations of the reactants and products don’t need to be equal
the concentrations of the reactants and products must remain constant
concentration change in the reaction

74
Q

the reaction from left to right is the

A

forward reaction

75
Q

the reaction from right to left is the

A

backward reaction

76
Q

what does the position of eqilibrium mean

A

a reference to the proportion of the reactants and products in an equilibrium mixture. if the position of a reaction lies towards the right, the equilibrium mixture contains a higher proportion of products than reactants.

77
Q

what things would you change in an attempt to influence the reaction

A

change the pressure
change the temperature
add a catalyst

78
Q

effect of increasing pressure on a reaction in equilibrium

A

the position of equilibrium shifts to the side which has fewer gas molecules

79
Q

effect of decreasing pressure on a reaction in equilibrium

A

the position of equilibrium shifts to the side which has fewer gas molecules.

80
Q

effect of increasing temperature on a reaction in equilibrium

A

the position of equilibrium shifts in the endothermic direction

81
Q

effect of decreasing temperature on a reaction in equilibrium

A

the position of equilibrium shifts in the exothermic reaction

82
Q

how would you make a reaction of hydrated to anhydrous substance happen

A

heat it

83
Q

how would you make a reaction of anhydrous to hydrated substance happen

A

add water

84
Q

specific heat capacity of water

A

4.18

85
Q

moles =

A

mass / Mr

86
Q

moles =

A

solution volume x concentration

87
Q

symbol for enthalpy change

A

ΔH

88
Q

symbol for energy change

A

Q

89
Q

moles =

A

gas volume / 24

90
Q

sources of error in combustion calorimetry

A

heat loss to surroundings
heat loss to apparatus
incomplete combustion (CO or C formed instead of CO2
evaporation of fuel (hot fuel escapes after burner extinguished)

91
Q

energy change for reaction (energetics) =

A

energy change in breaking bonds - energy change in making bonds
break - make

92
Q

unit for specific heat capacity?

A

J/g°C

or

J/kg°C

93
Q

what type of reaction is thermal decompistion

A

endothermic

94
Q

why do reactions either give out or absorb heat

A

during chemical reactions bonds in the reactants have to be broken and new ones have to be

95
Q

breaking bonds…

A

needs energy

96
Q

making bonds…

A

releases energy

97
Q

what is the rate of a reaction

A

the speed at which the amount of reactants decreases or the amount of products increases

98
Q

what is rate measured as

A

a change in the concentration (or amount) of reactants or products per unit time

99
Q

rate of reaction =

A

time

100
Q

the steeper the slope/line,

A

the faster the reaction

101
Q

how can you measure how fast the reaction is going at any point

A

by finding the slope (gradient) of the line at that point)

102
Q

how do you explain the shape of the curve on a graph

A

using collision theory

103
Q

what is activation energy

A

the particles have to collide with a minimum amount of energy in order for a reaction to actually happen.

104
Q

what are successful collisions

A

the collisions with energy greater than or equal to the activation energy

105
Q

when the graph’s line is flat or horizontal what does it mean

A

all of one of the reactants have been used up, so the reaction has stopped

106
Q

why are reactions faster if the solids present are in lots of pieces

A

the surface area in contact with the gas or liquid is larger and there are more particles if the solid exposed on the surface. only the particles on the surface are available for collisions. the frequency of successful collisions increases as the surface area of the solid increases.

107
Q

what is a catalytic converter

A

it uses expensive metals such as platinum coated onto a honeycomb structure in a very thin layer for maximum possible surface area.

108
Q

what happens if you reduce the concentration of an acid or alkali in a reaction

A

the reaction slows

109
Q

why does the reaction slow down when concentration is reduced

A

the number of acid particles decrease, are therefore less close together and collide less frequently. there are fewer succcessful collisions every second.

110
Q

why does increasing temperature speed up the rate of reaction

A

the particles are moving faster and so collide more frequently. that will make the reaction go faster, but it only accounts for a small part of the increase in rate. it also increases the number of particles with energy greater or equal to the activation energy, so it will be more likely that two particles which have sufficient energy will collide and react with each other, so frequency of successful collisions increases.

111
Q

why does increasing pressure increase rate of reaction

A

it forces particles closer together so that they collide more frequently.

112
Q

why does decreasing pressure decrease rate of reaction

A

it allows particles to spread out so frequency of successful collisions decreases.

113
Q

what are catalysts

A

substances that speed up chemical reactions but arent used up in the process. they remain chemically unchanged at the end of the reaction.

114
Q

do different reactions use different catalysts

A

yes

115
Q

what are enzymes

A

biological catalysts

116
Q

how can you show that a substance is chemically unchanged by the end of a reaction

A

weigh it before and after you add it to the catalyst solution. the mass should not have changed.

117
Q

how does a catalyst work

A

it provides an alternative route for the reaction involving a lower activation energy.

edexcel igcse chemistry (4 decks)

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