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CSEC CHEMISTRY > C5: Rates of Reaction and Thermochemistry > Flashcards

C5: Rates of Reaction and Thermochemistry Flashcards

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1
Q

what is the rate of a reaction

A

the change in the concentration of the product or reactant over unit time

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2
Q

what are the two ways that the rate of reaction can be measured

A
  • by measuring how quickly the reactants are used up - or measuring how quickly the product is formed
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3
Q

what are the 3 experimental measurements used to measure rate of reaction

A
  • precipitation - change in mass - volume of gas given off
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4
Q

what type of reactions would the method of precipitation work in

A
  • any reaction where mixing two see-through solutions produces a precipitate - which clouds the solution
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5
Q

what is a disadvantage of the precipitation method

A
  • the result is subjective - different people might not agree on exactly when the mark disappears
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6
Q

what is a mass balance used for

A

measuring the rate of a reaction that produces a gas

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7
Q

while measuring the change in mass, how does a mass balance indicate the rate of a reaction

A
  • during reaction, as gas is released - lost mass is easily measured on the balance - the quicker the reading on the balance drops, the faster the reaction
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8
Q

ho do you know when a reaction has finished in the change in mass method and why

A
  • when the reading on the balance stops changing - because no more mass is being lost - so no more gas is being released - meaning the reaction has stopped
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9
Q

how can your results in the change in mass method be visually displayed

A

by plotting a graph of change in mass against time

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10
Q

what is a disadvantage of the change in mass method

A
  • method releases gas produced into the room - if gas is harmful, safety precautions must be taken
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11
Q

how is the volume of gas given off in the ‘volume of gas given off’ method measured with

A

a gas syringe

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12
Q

how is a faster reaction indicated in the volume of gas given off method

A
  • more gas is given off during a set time interval - shown by the gas syringe filling up at a quicker rate
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13
Q

how can you tell when the reaction has finished in the volume of gas given off method

A

when no more gas is produced and the gas syringe reading doesnt change

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14
Q

how would you plot your results on a graph from the volume of gas given off method

A

you would plot the graph of gas volume against time elapsed

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15
Q

what is a disadvantage of the volume of gas given off method

A
  • need to be careful using youre the right size gas syringe - if reaction is too vigorous, the plunger can be blown off the end of the syringe
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16
Q

Give the 2 equations of how you can find the rate of reaction

A
  • Amount of reactant used/time
  • Amount of product formed/time
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17
Q

How can you find the rate of reaction from a graph?

A

The gradient

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18
Q

What is the relationship between rate and time?

A

They are inversely proportional; the faster the rate the shorter the time

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19
Q

What does collision theory state?

A
  • That reactions can only occur if particles collide.
  • The particles must collide with enough energy to react
  • The particles must collide with the correct orientation
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20
Q

What is the minimum energy required for substances to react called?

A

Activation energy

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21
Q

How do the different factors increase the rate of a reaction?

A

Factors that increase the chance of collisions or the energy of particles

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22
Q

5 factors that affect rates of reaction

A
  • Temperature
  • Concentration of solutions
  • Pressure of gases
  • Surface area of solids
  • Using a catalyst
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23
Q

How does surface area increase the rate of reaction?

A

Increasing the SA, exposes more of the surface. This means more frequent collisions in the same time and this increases the rate of reaction.

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24
Q

How does temperature effect the rate of reaction?

A

Temperature increases the speed of the particles, so they collide more often and with more energy. They also reach the activation energy required much quicker. This increases the rate of reaction

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25
Q

Roughly by how much will the rate of reaction will increase by if the temperature is increased by 10 degrees?

A

Double

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26
Q

How does the concentration or pressure effect the rate of reaction?

A

A higher concentration means more particles are dissolved in the same volume, meaning the particles are closer together and so collide more often

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27
Q

How do catalysts work?

A

They speed up reactions by lowering the activation energy of the reaction so more collisions result in a reaction.

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28
Q

Why can catalysts be reused?

A

It changes the rate of reaction but is not used up or reacts

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29
Q

What are the benefits of using catalysts in industrial processes?

A

The reduce the time and energy neede, saving money, conserve resources and reduce pollution. They can also be used again

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30
Q

Which group are catalysts from?

A

Transition metals

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31
Q

What are some disadvantages of catalysts?

A

Some are toxic and can cause harm in the environment

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32
Q

How does a catalyst work

A

They lower the activation energy as they provide an alternative pathway at a lower energy level so more successful collisions occur ^^ meaning they speed up reactions

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33
Q

How does a catalyst work

A

They lower the activation energy as they provide an alternative pathway at a lower energy level so more successful collisions occur ^^ meaning they speed up reactions

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34
Q

What do catalysts do and not do

A

They speed up reactions but are not used up

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35
Q

What do catalysts do and not do

A

They speed up reactions but are not used up

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36
Q

What is the meaning of a reversible reaction

A

A reaction that can be changed back to its original form > the reaction can go in both directions

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37
Q

What effect does a catalyst have on a rate of reaction

A

They lower the activation energy, providing a different pathway and a lower energy level so more successful collisions occur

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38
Q

What is the effect of temperature on rates

A

If increased the reactant particles move more quickly which means they have more energy and collisions happen more therefore the rate of reaction increases

39
Q

What affect does the surface area have on rates of a reaction

A

The fate will increase as more particles are exposed to the other reactant and more collision will therefore happen

40
Q

What is the mass of a substances measured with

A

Balance

41
Q

What is the mass of a substances measured with

A

Balance

42
Q

Whats the activation energy

A

The minimum energy needed for particles to react

43
Q

Is bond breaking an exothermic or endothermic reaction

A

An endothermic reaction because energy must be supplied to break existing bonds

44
Q

Is bond formation an exothermic or endothermic reaction

A

Exothermic reaction because energy is released when new bonds are formed

45
Q

What’s the equation for energy change

A

Energy if bond breaking - energy if bond making

46
Q

What’s the equation for enthalpy of reaction?

A

enthalpy of products - enthalpy of reactants

47
Q

Give some facts on ammonia

A

It breaks down when it is heated It’s a colourless gas

48
Q

How do you work out the amount of energy given out from bond making

A

Adding up the bond energies of all the bonds in all the products

49
Q

What is a closed system

A

When I neither reactants nor products can enter or leave

50
Q

What is the position of equilibrium

A

When reversible reactions reach a balance point, where the amount of reactants and the amount of products formed remain constant

51
Q

What is a closed system

A

When I ether reactants nor products can enter or leave

52
Q

When is an equilibrium reached

A

When the forward and reverse reactions occur at the exactly same rate

53
Q

What is the position of equilibrium

A

When reversible reactions reach a balance point, where the amount of reactants and the amount of products formed remain constant

54
Q

How is a does concentration change the position of equilibrium

A

If more of a reactant is added, the system would work by removing this reactant and making more of the products

55
Q

How does temperature change the position of equilibrium

A

Decreasing the temp moves the position of E in the direction of the exothermic reaction Increasing the temp moves the position of E in the endothermic direction

56
Q

How is a does concentration change the position of equilibrium

A

If more of a reactant is added, the system would work by removing this reactant and making more of the products

57
Q

How does changing the pressure effect the post Position of equilibrium

A

Increasing the pressure moves the position of E to the suede with the least number of molecules

58
Q

How does changing the pressure effect the post Position of equilibrium

A

Increasing the pressure moves the position of E to the suede with the least number of molecules

59
Q

What happens if activation energy is low

A

Particles don’t need to collide with much energy to react Meaning they’ll react as soon as they’re mixed

60
Q

What happens if activation energy is low

A

Particles don’t need to collide with much energy to react Meaning they’ll react as soon as they’re mixed

61
Q

What can’t you do if two reactants are gases And what the alternative thing to do

A

Increase the concentration So you increase the pressure

62
Q

How can the rate of reaction between marble chips and hydrochloride acid be changed

A

Changing the temperature and surface area of reactants

63
Q

Why are powders like icing sugar flour and custard powder dangerous

A

They react very quickly as they have very large surface areas so they need to avoid naked flames

64
Q

What are the pros of catalysts

A

Very small amounts can be used and they can be used again and again thus many industrial chemical reactions use them

65
Q

What is a drawback if catalysts

A

They are very specific to what they can be used on

66
Q

What are catalysts in living things called

A

Enzymes Sometimes known as biological catalysts

67
Q

When do reactions stop

A

when one or both of the reactants are used up

68
Q

What is the reactant called that causes the reactions to stop

A

Limiting reactant

69
Q

How to measure the rate of reaction on a graph on a fine point on the graph

A

Make a tangent (straight line) on the curve of where the point asked is Then draw a right angles triangle and find the steepness of the tangent by dividing the height by the width Thus = vol. gas collected (divided) time taken

70
Q

To measure reactions rates what do you need to do

A

Observe the reaction at time intervals see amount of gas released Change in mass The colour or appearance change

71
Q

How to measure the rate of reaction on a graph on a fine point on the graph

A

Make a tangent (straight line) on the curve of where the point asked is Then draw a right angles triangle and find the steepness of the tangent by dividing the height by the width Thus = vol. gas collected (divided) time taken

72
Q

what would happen if you were to increase the number of collisions or the energy with which the particles collide with

A

the reactions would happen more quickly

73
Q

why does an increase in temperature result in an increase of rate of reaction in terms of kinetic energy

A
  • particles are given more kinetic energy so they move faster - faster movement results in more frequent collisions with other fast moving particles
74
Q

what is meant by a solution becoming more concentrated

A

there are more particles of reactant in the same volume

75
Q

what is the word used to describe the concentration of gases in a given volume

A

pressure

76
Q

how does breaking a solid reactant into smaller pieces affect rate of reaction

A

breaking a solid reactant into smaller pieces would increase the rate of reaction

77
Q

even though we use a catalyst, why does the reaction equation remain the same

A

because a catalyst doesnt change the products of a reaction, especially because it isnt used up

78
Q

if a catalyst isnt used up, how can it be effectively used in reactions

A

only a tiny bit needs to be used in order to catalyse large amounts of reactants

79
Q

what do reaction profiles show

A

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

80
Q

what is a endothermic reaction

A

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

81
Q

what is an exothermic reaction

A

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

82
Q

what can you use a reaction profile to do in terms of exo and endothermic reactions

A

you can use it work out if energy is released (exothermic) or taken in (endothermic)

83
Q

how is an exothermic reaction shown on a reaction profile

A

the products are at a lower energy level than the reactants

84
Q

how is an endothermic reaction shown on a reaction profile

A

the products are at a higher energy level than the reactants

85
Q

what indicates the activation energy in a reaction profile

A

the difference between the reactants and the highest point on a curve

86
Q

what would happen if the energy input is less than the activation energy

A

there wont be enough energy to start a reaction, so nothing would happen

87
Q

In terms of energetics, what kind of reaction is this?

A

exothermic

88
Q

In terms of energetics, what kind of reaction is this?

A

endothermic reaction

89
Q

define enthalpy of solution

A

the heat change when 1 mol of solute completely dissolves in a solvent

90
Q

define enthalpy or heat of neutralization

A

the heat change when 1 mol of water is produced in a neutralization reaction

91
Q

define heat of combustion

A

the heat change when 1 mol of a compound is completely burned in oxygen

92
Q

Enthalpy of formation

A

heat change when 1 mole of a substance is formed from its elements under standard conditions

93
Q

if the temperature is given, what is the equation for enthalpy or heat of reaction

A

CSEC CHEMISTRY (17 decks)

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