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Chemistry GCSE > Topic 7 - Rates of Reaction and Energy Changes > Flashcards

Topic 7 - Rates of Reaction and Energy Changes Flashcards

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1
Q

What is the rate of a reaction?

A

How quickly a reaction happens

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2
Q

How can you observe the rate of reaction?

A

How quickly reactants are used up

How quickly products are formed

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3
Q

What is the rate of reaction equation?

A

Rate of Reaction = (Amount of reactant used or amount of product formed) / Time

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4
Q

What are the experiments to measure the rate of reaction?

A

Change in mass
Precipitation
Volume of gass given off

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5
Q

What is the precipitation experiment?

A

Using two see-through solutions to form a precipitate which clouds a mark

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6
Q

What is the problem with the precipitation experiment?

A

Subjective as different people might not agree on exactly when the mark disappears

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7
Q

How do you measure the rate of reaction that produces a gas?

A

By using a mass balance

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8
Q

When using change in mass to measure the rate of reaction, how do you tell the reaction is finished?

A

The mass balance stops changing

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9
Q

What risks are associated with measuring the volume of gas to calculate the rate of reaction?

A

The plunger may be blown out of the syringe if the reaction is too vigorous

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10
Q

Outline how you could use a mass balance to measure the rate of a reaction where a gas is formed?

A

Put a conical flask on a mass balance and add your reactants. As gas is produced from the reaction, measure how quickly the reading on the balance drops until the balance stops changing

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11
Q

Give one disadvantage of the precipitation method when used to follow the rate of a reaction?

A

No quantitive result (except time, no amount of reactant used or product formed)
Subjective meaning different people might not agree on exactly when the mark ‘disappears’

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12
Q

How can you measure how surface area affects the rate of reaction?

A

Add marble chips to dilute HCL and measure the gas released

Each time crunch the chips up more and more, increasing the surface area, whilst keeping the mass the same

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13
Q

What does finer particles of solid mean?

A

A higher rate of reaction

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14
Q

How can you increase the volume of gas produced in a reaction?

A

By increasing the mass of the reactants

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15
Q

How can you measure how concentration affects the rate of reaction?

A

Add marble chips to dilute HCL and measure the gas released

Each time increasing the concentration of acid

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16
Q

Describe how you could investigate how the surface area of calcium carbonate affects the rate of reaction between calcium carbonate and hydrochloric acid?

A

Place a measured volume of HCL of a known conc in a conical flask
Add a known mass of calcium carbonate in the form of marble chips
Immediatly add a gas syringe and take readings of the volume of gas produced
Repeat the experiment but with the calcium carbonate crushed

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17
Q

What reactants are used to investigate the effect of temperature on the rate of reaction?

A

Sodium thiosulfate

Hydrochloric acid

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18
Q

What do sodium thiosulfate and hydrochloric acid react to form?

A

A yellow precipitate of sulfur

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19
Q

Briefly describe the method of investigating temperature and reaction rate

A

Measure out fixed volumes of sodium thiosulfate and hydrochloric acid
Heat the reactants to a desired temperature and mix the solutions
Time how long it takes for the precipitation to make the black mark disappear
Repeat experiment at different temperatures

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20
Q

Briefly describe the method of investigating temperature and reaction rate

A

Measure out fixed volumes of sodium thiosulfate and hydrochloric acid
Heat the reactants to a desired temperature and mix the solutions
Time how long it takes for the precipitation to make the black mark disappear
Repeat experiment at different temperatures

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21
Q

When measuring how surface area affects ROR, what are the control variables?

A

The same volume and concentration of acid

The same mass of marble chips

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22
Q

When measuring how concentration affects ROR, what are the control variables?

A

The same mass and surface area of marble chips

The same volume of hydrochloric acid

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23
Q

What does a higher temperature mean?

A

A higher rate of reaction

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24
Q

Azim carries out an experiment to measure how temperature affects the rate of reaction between sodium thiosulfate and hydrochloric acid
He uses the time taken for a mark underneath the reaction vessel to be obscured as a measure of rate
How would you expect the time taken for the mark to disappear to change as the temperature of the reacting solutions were increases?

A

As the temperature of the reacting solutions increases, the time taken for the mark to disappear decreases

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25
Q

What must particles collide with to react?

A

Enough energy

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26
Q

What does the rate of a chemical reaction depend on?

A

The collision frequency of reacting particles

The energy transferrred during a collision

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27
Q

What is activation energy?

A

The minimum energy that particles need to react when they collide, so bonds can be broken and a reaction can start

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28
Q

The more collisions, the ____ the rate of reaction

A

The more collisions, the higher the rate of reaction

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29
Q

What are the three factors that affect the rate of reaction?

A

Temperature
Concentration
Surface Area

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30
Q

How does temperature affect the ROR?

A

Increasing the temperature will:
Cause particles to move faster causing a higher frequency of collisions therefore the ROR will increase
Give particles more energy causing a higher frequency of successful collisions therefore the ROR will increase

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31
Q

How does concentration affect the ROR?

A

Increasing the concentration will:
Mean there are more particles of reactant in the same volume meaning collision are more likely therefore the ROR will increase

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32
Q

How does pressure affect the ROR?

A

Increasing the pressure will:

Mean particles are more crowded meaning there will be a higher frequency of collisions therefore the ROR will increase

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33
Q

How does surface area affect the ROR?

A

Increasing the surface area will:
Mean there is more area for collisions to take place meaning there will be a higher frequency of collisions therefore the rate of collisions will increase

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34
Q

What does an increased frequency of collisions lead to?

A

An increased number of sucessful collisions

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35
Q

Describe the two factors, in terms of collisions, that affect the rate of reaction

A

The energy transferred during a collisions must exceed the activation energy
The collisions frequency

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36
Q

Explain why breaking a solid reactant into smaller pieces increases the rate of reaction

A

Breaking a solid into smaller pieces will increases the surface area to volume ratio meaning there will be a more area for reactions to take place meaning the frequency of collisions will speed up therefore the number of sucessful collisions will increase

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37
Q

What is a catalyst?

A

A substance which increases the rate of a reaction without being chemically changed or used up

38
Q

Does a catalyst have an affect on the chemical equation?

A

No it will have no affect on the products or reactants

39
Q

What is good about a catalyst?

A

It isnt used up meaning you only need a tiny bit to catalyse large amounts of reactants

40
Q

How do catalysts work?

A

By lowering the activation energy by providing an alternative reaction pathway that has a lower activation energy

41
Q

What are enzymes?

A

Biological catalysts

42
Q

What are enzymes used for?

A

Respiration
Photosynthesis
Protein Synthesis

43
Q

What do reaction profiles show?

A

The energy levels of the reactants and the products in a reaction

44
Q

What do enzymes in fermentation do?

A

Catalyse the reaction that converts sugars into ethanol and carbon dioxide

45
Q

The decomposition of hydrogen peroxide can be catalysed by manganese dioxide
Explain why only a small amount of manganese dioxide is needed for the catalysis of this reaction, even when starting with a large quantity of hydrogen peoxide

A

Catalysts are not used up or chemically changed in a reaction meaning you can use a small amount to catalyse a large quantity of reactant

46
Q

What is an exothermic reaction?

A

A reaction which gives out energy to the surroundings, usually in the form of heat and usually shown by a rise in temperature of the surroundings

47
Q

What is an endothermic reaction?

A

A reaction which takes in energy from the surroundings, usually in the form of heat and usually shown by a fall in temperature of the surroundings

48
Q

How can you tell if a reaction is exothermic?

A

There is a rise in the surrounding temperature

49
Q

How can you tell if a reaction is endothermic?

A

There is a decrease in the surrounding temperature

50
Q

What will a exothermic reaction profile look like?

A

The products will be at a lower energy than the reactants and the difference in height will represent the energy given out in the reaction

51
Q

What will a endothermic reaction profile look like?

A

The products will be at a higher energy than the reactants and the difference in height will represent the energy taken in during the reaction

52
Q

What is the activation energy on a reaction profile?

A

The difference between the peak and the reactant energy

53
Q

A student carries out an experiment which results in a change in temperature of the reaction mixture.
They notice the reactants have less energy than the products, explain whether what type of reaction this must be?

A

Endothermic as the products have gained energy from the surroundings

54
Q

How do you measure the temperature change because of a reaction?

A

Put a polystyrene cup into a beaker of cotton wool
Add a known volume of a reagent to the cup and measure the inital temperature of the solution
Add a measured mass of the second reagant and stir
Record the maximum and minimum temperature and then calculate the temperature change

55
Q

Why is cotton wool used in measuring temperature change?

A

Because it gives insulation to help limit energy transfer to or from the reaction mixture

56
Q

Why is a lid put on the apparatus when measuring temperature change?

A

To reduce energy lost by evaporation

57
Q

What type of reaction is dissolving salt in water?

A

Endothermic and exothermic

58
Q

What type of reaction is neutralisation?

A

Mostly exothermic

59
Q

What type of reaction is endothermic?

A

Exothermic

60
Q

What type of reaction is precipitation?

A

Exothermic

61
Q

When measuring the temperature change of a reaction, why is it important to put the polystyrene cup in a beaker of cotton wool and to keep a lid on the cup?

A

They help to insulate the reaction mixture, limiting the energy transferred to or from the surroundings and by evapouration

62
Q

What must be supplied during a reaction?

A

Energy must be supplied

63
Q

What actually happens in a chemical reaction?

A

Old bonds are broken and new bonds are formed

64
Q

What type of process is bond breaking?

A

Endothermic

65
Q

What type of process is bond building?

A

Exothermic

66
Q

Describe the energy from bond change for a endothermic reaction

A

More energy is used to break bonds than released by forming the bonds

67
Q

Describe the energy from bond change for a exothermic reaction

A

More energy is released by forming bonds than used to break bonds

68
Q

How do you remember the overall energy change equation?

A

Break and Entering

Broken - Erected

69
Q

What is the energy change equation?

A

Energy change = Energy required to break bonds - Energy released by forming bonds

70
Q

What is a positive energy change?

A

An endothermic reaction

71
Q

What type of energy change is for an endothermic reaction?

A

A positive

72
Q

What is a negative energy change?

A

An exothermic reaction

73
Q

What type of energy change is for an exothermic reaction?

A

A negative

74
Q

Using the bond energy values below, calculate the energy change for the following reaction, where hydrogen and chorine react to product hydrogen chloride

H-H 436
Cl-CL 242
H-Cl 431

A

H2 + Cl2 ->2HCl
H-H + Cl-Cl -> 2H-Cl

436 + 242 -> 862
678 - 862 = -184

75
Q 
N2 + 3H2 -> 2NH3
N=N 941
H-H 436
N-H 391
Calculate the overall energy change for the forward reaction
A

941 + 3(436) = 2249
6(391) = 2346

2249 - 2346 = -97

76
Q

A student carries out a reaction which produces CO2
He collects the CO2 in a gas syringe
How will he know when the reaction has finished

A

The gas syringe stops moving (changing volume)

77
Q

Explain how you could follow the ROR where two colourless solutions react to form a precipitate

A

Add solutions to conical flask above a mark that you can see from the birds eye view
Time how long it takes for the mark to disappear

78
Q

When undergoing the precipitation reaction to measure the ROR, why must the solutions be colourless?

A

So you can see the mark before the reaction has begun

79
Q

How does the rate of the reaction between sodium thiosulfate and hydrochloric acid change with temperature?

A

Increases

As particles have more energy meaning more sucessful collisions whilst also moving more meaning more collisions

80
Q

Describe how you would find the rate of reaction from a straight line graph?

A

Find the gradient

81
Q

What effect will raising the temperature have on the ROR?

A

Increase the ROR

82
Q

What effect will raising the temperature have on the time taken for a reaction?

A

Decrease it

83
Q

What graph is the graph showing temperature and time taken for a reaction?

A

The inverse proportion graph

84
Q

How does concentration affect the rate of reaction?

A

Increases the rate of reaction

As there will be more reactants meaning there will be a higher frequency of collisions

85
Q

In a gaseous reaction, why would a decrease in pressure result in a slower rate of reaction?

A

Because less pressure means the particles are less packed together meaning there will be less collisions therefore there will be a slower rate of reaction

86
Q

What effect does a catalyst have on the activation energy needed for a reaction to take place?

A

The catalyst lowers the activation energy

87
Q

Give two examples of reactions catalysed by enzymes

A 
Any two from:
Respiration
Photosynthesis
Protein synthesis
Digestion
88
Q

What change in temperature would you expect to observe in an exothermic reaction?

A

Increase in surroundings

89
Q

Describe how you could measure the temperature changes in a neutralisation reaction?

A

Put polysteryene cup into beaker of cotton wool
Add known volume of alkali and acid and put lid on
Measure temperature change

90
Q

Is energy required for the breaking of bonds or the forming of bonds?

A

The breaking of bonds

Chemistry GCSE (9 decks)

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