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Chemistry Year 11 Content > Rates Of Reaction > Flashcards

Rates Of Reaction Flashcards

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1
Q

Reactions can go at all sorts of different

A

Rates

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2
Q

What is the rate of a chemical reaction?

A

The rate of a chemical reaction is how fast the reactants are changed into products.

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3
Q

Examples of slow reactions

A 
The rusting of iron 
Chemical weathering (acid rain damage to limestone buildings)
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4
Q

Example of a moderate speed reaction

A

Metal magnesium reacting with an acid to produce a gentle stream of bubbles

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5
Q

Burning is a ____ reaction.

A

Fast reaction. But explosions are even faster and release a lot of gas. Explosive reactions are all over in a fraction of a second.

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6
Q

How can you find the speed of a reaction

A

Recording the amount of product formed or the amount of reactant used over time

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7
Q

Rate of reaction - the steeper the line on the graph

A

The faster the rate of reaction. Over time the line becomes less steep as the reactants are used up.

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8
Q

The quickest reactions have the steepest lines and

A

Become flat in the least time as the reactants are used up

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9
Q

Particles must collide with ________ in order to react

A

Enough energy

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10
Q

Reaction rates are explained perfectly by the

A

Collision theory

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11
Q

Collision theory

A

The rate of chemical reaction depends on- The collision frequency of reacting particles (how often they collide) More collisions, faster reaction
The energy transferred during a collision. Particles need to collide with enough energy for the collision to be successful

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12
Q

Activation energy

A

The minimum amount of energy particles need to react. Particles need this energy to break the bonds in the reactants and start the reaction.

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13
Q

What will increase the rate of reaction

A

Factors that increase the number of collisions (So a greater proportion of reaction particles collide) or the amount of energy particles collide with will increase the rate of the reaction.

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14
Q

Which 4 things does the rate of reaction depend on?

A

Temperature
Concentration of solution or pressure of gas
Surface area (changes depending on the size of the lumps of a solid)
Presence of a catalyst

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15
Q

More collisions increase the

A

Rate of reaction

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16
Q

All four methods of increasing the rate of a reaction can be explain in terms of

A

Increasing the number of successful collisions between reacting particles

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17
Q

Increasing the temp

A

Increases the rate

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18
Q

When temperature is increased

A

The particles all move faster

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19
Q

If the particles are moving faster

A

They are going to collide more frequently

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20
Q

Also the faster the particles move the more energy they have

A

So more of the collisions will have enough energy to make the reaction happen

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21
Q

Increasing the conc or pressure

A

Increases the rate

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22
Q

If a solution is more concentrated

A

It means there are more particles in the same volume of water (or other solvent)

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23
Q

When the pressure of a gas is increased

A

It means that the same number of particles occupies a smaller space. This makes collisions between the reactant particles more frequent

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24
Q

Increasing the SA

A

Increases the rate

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25
Q

If one of the reactants is a solid

A

Then breaking it up into smaller pieces will increase its SA: V RATIO

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26
Q

For the same volume of the solid

A

The particles around it will have more area to work on so collisions are more frequent

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27
Q

Using a catalyst

A

(You guesses it) increases the rate

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28
Q

A catalyst is a substance that speeds up a reaction without being used up in the reaction itself which means

A

It’s not part of the overall reaction equation

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29
Q

Different catalysts are needed for different reactions

A

But they all work by decreasing the activation energy needed for the reaction to occur.

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30
Q

Catalysts decrease the activation energy needed by

A

Providing an alternative reaction pathway with a lower activation energy

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31
Q

Enzymes are biological catalysts

A

They catalyse reactions in living things.

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32
Q

Three ways of measuring rate of reaction

A

Precipitation and colour change
Change in mass (usually given off)
The volume of gas given off

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33
Q

Mean Rate of reaction equation

A

ROR = amount of reactant used or amount of product formed / time

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34
Q

How to find the rate of reaction at a specific time

A

Plot a graph and find the gradient at that time

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35
Q

When the product is a gas

A

You usually measure the amount in cm3

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36
Q

If the product or reactant is a solid

A

You measure in grams

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37
Q

Time is often measure in

A

Seconds

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38
Q

The units for rate may be in

A

Cm3/s or in g/s

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39
Q

You can also measure the amount of product or reactant in moles

A

Measurement could be mol/s

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40
Q

You can record the visual change in a reaction if

A

The initial solution is transparent and the product is a precipitate which clouds the solution (it becomes opaque)

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41
Q

You can observe a mark through the solution and measure how long it takes for it to disappear

A

The faster the mark disappears the faster the reaction

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42
Q

If the precipitation products are colourless or vice versa,

A

You can time how long it takes for the solution to lose or gain its colour

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43
Q

In precipitation why are the results very subjective?

A

Different people might not agree over the exact point when the mark disappears or the solution changes colour.

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44
Q

What can you not do if you use the precipitation method

A

Can’t plot the rate of reaction graph from the results

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45
Q

What is a mass balance used for?

A

To measure the speed of the reaction that produces a gas.

46
Q

How is the mass balance used?

A

As the gas is released the mass disappearing is measured

47
Q

The quicker the reading on the mass balance drops…

A

The faster the reaction

48
Q

When measuring the change in mass, how would you plot the rate of reaction graph?

A

if you take measurements at regular intervals You can plot the rate of reaction graph and find the rate quite easily

49
Q

Change in mass method is the most…

A

Accurate method of three

50
Q

Why is the change in mass method the most accurate?

A

Because the mass balance is very accurate

51
Q

Disadvantage of change in mass method

A

Releasing gas straight into the room

52
Q

The volume of gas given off involves

A

The use of a gas syringe to measure the volume of gas given off

53
Q

The more gas given off during a given time interval

A

The faster the reaction

54
Q

Gas syringes usually give volumes accurate to the

A

Nearest cm3 so they are quite accurate

55
Q

How to plot a graph using the volume of gas given off method

A

Taking measurements at regular time intervals

56
Q

Why do you have to be careful while using the volume of gas given off method

A

Because if the reaction is too vigorous you can easily blow the plunger out the end of the syringe

57
Q

2 examples of measuring the effect of concentration on the rate of reaction

A

Mg and HCL react to produce H2 gas

Sodium thiosulfate and HCL produce a cloudy precipitate

58
Q

Step 1 of Mg + HCL —

A

Ass a set volume of dilute HCL to a conical flask and carefully place it on a mass balance

59
Q

Step 2 of Mg + HCL —

A

Add some Mg ribbon to the acid and quickly plug the flask with cotton wool

60
Q

Step 3 of Mg + HCL —

A

Start the stopwatch and record the mass on the balance. Take readings of the mass at regular intervals

61
Q

Step 4 of Mg + HCL —

A

Plot the results in a table and work out the mass lost for each reading. Plot a graph with time on the x axis and loss of mass on the y axis

62
Q

Step 5 of Mg + HCL —

A

Repeat with more conc acid solutions. Variables such as the amount of Mg ribbon and the vol of acid should be kept the same each time - only change the acids conc.

63
Q

Why do we keep the amount of mg ribbon and vol of acid the same each time in step 5?

A

To make the experiment a fair test

64
Q

Step 6 of Mg + HCL —

A

The three graphs will show that a higher conc of acid gives a faster rate of reaction.

65
Q

On the Mg + HCL —

A

Most conc on top, least conc on bottom

66
Q

Step 1 of Na thiosulfate + HCL —

A

Add a set volume of dilute sodium thiosulfate to a conical flask

67
Q

Na thiosulfate + HCL are both

A

Clear solutions. They react together to form a yellow precipitate of sulfur

68
Q

Step 2 of Na thiosulfate + HCL —

A

Place the flask on a piece of paper with a black cross drawn on it. Add some dilute HCL and start the stopwatch

69
Q

Step 3 of Na thiosulfate + HCL —

A

Black cross will disappear through the cloudy silver and time how long it takes to go

70
Q

Step 4 of Na thiosulfate + HCL —

A

The reaction can be repeated with solutions of either reactant at different concentrations. The depth of the liquid must be kept the same each time.

71
Q

What do the results show of Na thiosulfate + HCL —

A

The effect of increasing the conc of HCL on the rate of reaction, when added to an excess of sodium thiosulfate

72
Q

When should the Na thiosulfate + HCL —

A

Releases sulfer dioxide so it needs to take place in a well ventilated place

73
Q

Why does it take less time for the mark to disappear in Na thiosulfate + HCL —

A

Because the higher the conc, the faster the reaction

74
Q

Disadvantage of Na thiosulfate + HCL —

A

Doesn’t give a set of graphs. Gives a set of readings of how long it took until the mark disappeared for each conc

75
Q

What can you calculate from a reaction graph?

A

Mean reaction rate (and mean reaction rate between any two points in time)

76
Q

What does a rate of reaction graph show?

A

The amount of product formed or amount of reactant used up over time

77
Q

How to find the mean rate for the whole reaction using a graph

A

Work out the overall change in the y value and then divide this by the total time taken for the reaction

78
Q

Mean ROR =

A

Change in y / change in x

79
Q

How to find the rate of reaction at a PARTICULAR POINT on a graph

A

Draw a tangent

80
Q

How to do a tangent

A

Draw a line which touches the point on the graph you want and make sure the curve is equal on both sides of the point
Extend it right across the graph
Calculate the gradient of tangent (do the triangle thing)

81
Q

Gradient =

A

Change in y / change in x

82
Q

Some reactions can go…

A

Backwards

83
Q

Reversible reactions will reach

A

Equilibrium

84
Q

As the reactants react

A

The forward reaction will slow down

85
Q

As more products we made and their concentrations rise

A

The backward reaction will speed up

86
Q

After a while of the forward reaction slowing and the backward reaction getting faster

A

Both reactions will be going at exactly the same rate

87
Q

When both reactions are going at exactly the same rate the system is at

A

Equilibrium

88
Q

At equilibrium both reactions are still happening but

A

There’s no overall effect (dynamic equilibrium) so the conc of the r and p have reached balance and won’t change

89
Q

Equilibrium is only reached if the reversible reaction takes place in a

A

Closed system

90
Q

What is a closed system?

A

None of the reactants or products can escape and nothing can get in

91
Q

Position of the equilibrium can be on the

A

Right or left

92
Q

When reactions at equilibrium it doesn’t mean…

A

The amounts of reactants and products are equal

93
Q

If the equilibrium right lies to the right

A

The concentration of products is greater than that of the reactants

94
Q

If the equilibrium lies to the left

A

The conc of the reactants is greater than that of the products

95
Q

The position of the equilibrium relies on the following conditions

A

The temp
The pressure (only effect equilibria involving gases)
The conc of the reactants and products

96
Q

Reversible reactions can be e…

A

Endothermic and exothermic

97
Q

In reversible reactions if the reaction is endothermic in one direction

A

It will be exothermic in the other

98
Q

The energy transferred from the surroundings by the endothermic reaction is equal to

A

The surroundings during the exothermic reaction

99
Q

A good example of exo and endo reversible reactions is

A

Thermal decomposition of hydrated copper sulfate
Heat blue hydrated copper sulfate crystals it leaves white anhydrous copper sulfate powder which is endo. Reverse thing and it’s exo

100
Q

What is Le Chateliers principle?

A

If you change to conditions of a reversible reaction at equilibrium the system will try to counteract the change

101
Q

What can Le Chateliers principle be used to do

A

To predict the effect of any changes you make to a reaction system

102
Q

All reactions are…

A

Exothermic in one direction and endothermic in the other.

103
Q

What will happen if you decrease the temperature?

A

The equilibrium will move in the exothermic direction to produce more heat.

104
Q

When the equilibrium shifts what will you get?

A

More products in one reaction and fewer products in the other (either exo or endo)

105
Q

If you raise the temperature…

A

The equilibrium will move in the endothermic direction to try and decrease it. More products for endo and less products for the exo

106
Q

Changing the pressure…

A

Only affects an equilibrium involving gases.

107
Q

If you increase the pressure,

A

The equilibrium tries to reduce it - it moves in the direction where there are fewer molecules of gas.

108
Q

If you decrease the pressure

A

The equilibrium tries to increase it - it moves in the direction where there are more molecules of gas.

109
Q

What equation can you use for a reaction to see which side has more molecules of gas?

A

Balanced symbol equation.

110
Q

If you change the conc of either of the reactant or the products…

A

The system will no longer be at equilibrium

111
Q

If you increase the conc of the reactants the system tries to decrease it by making more

A

system tries to decrease it by making more products

112
Q

If you decrease the concentration of products

A

The system tries to increase it again by reducing the amount of reactants.

Chemistry Year 11 Content (9 decks)

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