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Chemistry IGCSE CIE Extended > 7. Chemical Reactions > Flashcards

7. Chemical Reactions Flashcards

1
Q

What do physical changes produce?

A

Physical changes (such as melting or evaporating) do not produce any new chemical substances

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2
Q

Are physical changes hard to reverse?

A

NO

-These changes are often easy to reverse and mixtures produced are usually relatively easy to separate

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3
Q

What do chemical changes produce?

A

In chemical reactions, new chemical products are formed that have very different properties to the reactants

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4
Q

Are chemical changes hard to reverse?

A

YES

- Most chemical reactions are impossible to reverse

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5
Q

What accompany chemical changes?

A

Energy changes also accompany chemical changes and energy can be given out (exothermic) or taken in (endothermic)

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6
Q

Are the majority of chemical reactions exothermic or endothermic?

A

The majority of chemical reactions are exothermic with only a small number being endothermic

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7
Q

What is the correlation between the rate of reaction and the concentration of a solution?

A

Increase in the concentration of a solution, the rate of reaction will increase

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8
Q

Why does an increase in concentration lead to an increase in the rate of reaction?

A

This is because there will be more reactant particles in a given volume, allowing more frequent and successful collisions per second, increasing the rate of reaction

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9
Q

What is the correlation between the rate of reaction and the surface area of a substance?

A

Increase in the surface area of the solid, the rate of reaction will increase

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10
Q

Why does an increase in surface area lead to an increase in the rate of reaction?

A

This is because more surface area particles will be exposed to the other reactant so there will be more frequent and successful collisions per second, increasing the rate of reaction

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11
Q

What is the correlation between the rate of reaction and temperature?

A

Increase in the temperature, the rate of reaction will increase

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12
Q

Why does an increase in temperature lead to an increase in the rate of reaction?

A

This is because the particles will have more kinetic energy than the required activation energy, therefore there will be more frequent and successful collisions per second, increasing the rate of reaction

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13
Q

What is the correlation between the rate of reaction and the use of a catalyst?

A

This shows that when a catalyst is used, the rate of reaction will increase

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14
Q

Why does the use of a catalyst lead to an increase in the rate of reaction?

A

Catalysts reduce the activation energy as they create alternative pathways requiring lower activation energy, allowing more successful and frequent collisions

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15
Q

When does explosive combustion occur?

A

Explosive combustion occurs when there are many fine particles in the air

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16
Q

In what industrial processes is there a high risk of explosive combustion and why?

A

Many industrial processes such as metal working, coal mining or flour milling produce very fine and tiny particles
These particles have a very large surface area and are combustible in air
Even a small spark may cause them to ignite and since the surface area is so large, the rate of reaction can be incredibly fast, hence they are explosive

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17
Q

Describe the graph for using different concentrations to see their effect on the rate of reaction

A

Compared to a reaction with a reactant at a low concentration, the graph line for the same reaction but at a higher concentration has a steeper gradient at the start and becomes horizontal sooner

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18
Q

Describe the graph for using different surface areas to see their effect on the rate of reaction

A

Compared to a reaction with lumps of reactant, the graph line for the same reaction but with powdered reactant has a steeper gradient at the start and becomes horizontal sooner

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19
Q

Describe the graph for using a catalyst to see their effect on the rate of reaction

A

The diagram shows that when a catalyst is used, the activation energy is reduced as it creates an alternative pathway requiring lower activation energy, allowing more successful and frequent collisions

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20
Q

Describe the graph for using different temperatures to see their effect on the rate of reaction

A

Compared to a reaction at a low temperature, the graph line for the same reaction but at a higher temperature has a steeper gradient at the start and becomes horizontal sooner

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21
Q

Look at 7.1.2 and the different practicals

A

indeed

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22
Q

What is the activation energy?

A

Particles need to have a minimum amount of energy to react when they collide
This is called the activation energy

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23
Q

Why is the rate of reaction slow at low temperatures?

A

At low temperatures only a small number of particles will have enough activation energy so the reaction will be slow

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24
Q

Why is the rate of reaction higher at higher temperatures? in terms of kinetic energy

A

At higher temperatures the particles have more kinetic energy so they move faster and with more energy
The collisions are thus more energetic and there is a greater number of particles with sufficient energy to react, so the rate of reaction increases

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25
What does increasing the concentration do in relation to space and how does this increase the rate of reaction?
Increasing the concentration means there are more particles per cm3, so there is less space between the particles Since there are more particles then it follows that there are more collisions, hence the rate of reaction increases
26
In what conditions do photochemical reactions occur?
These reactions occur only when light is present
27
What increases the rate of photochemical reactions?
The greater the intensity of ultraviolet light then the greater the rate of reaction
28
What is an example of a photochemical reaction? Give an equation
Photosynthesis | 6CO2 + 6H2O ---> C6H12O6 + 6O2
29
What do black and white photography film surfaces contain?
crystals of silver bromide
30
What happens to silver bromide when exposed to light? Give an equation?
When exposed to light they decompose to silver: | 2AgBr → 2Ag + Br2
31
What is the difference in colour between AgBr and Ag
AgBr - colourless at low concentrations | Ag - appears grey black
32
What causes the different shades of black on a photography film?
Parts of the film appear black, grey or white depending on the exposure: Stronger light = black or dark grey Weaker light = light grey Not exposed = white
33
What is photosynthesis?
This is the process in which plants produce food for reproduction and growth
34
What does photosynthesis require?
The process requires sunlight and chlorophyll
35
What is the catalyst for photosynthesis?
Chlorophyll is the green pigment in plants which absorbs sunlight and acts as the catalyst for photosynthesis
36
When do most reactions go to completion?
Some reactions go to completion, where the reactants are used up to form the product molecules and the reaction stops when all of the reactants are used up
37
What is the difference with reversible reactions compared to normal reactions?
In reversible reactions, the product molecules can themselves react with each other or decompose and form the reactant molecules again
38
In which direction does a reversible reaction occur?
It is said that the reaction can occur in both directions: the forward reaction (which forms the products) and the reverse direction (which forms the reactants)
39
What symbol is used to indicate a reversible reaction?
⇌
40
What is an example of a reversible reaction?
N2 + 3H2 ⇌ 2NH3
41
What are hydrated salts?
Hydrated salts are salts that contain water of crystallisation which affects their molecular shape and colour
42
What is water of crystallisation?
Water of crystallisation is the water that is stoichiometrically included in the structure of some salts during the crystallisation process
43
What is a common example of a hydrated salt?
A common example is copper(II) sulfate which crystallises forming the salt copper(II) sulfate pentahydrate, CuSO4.5H2O
44
How is water of crystallisation indicated?
Water of crystallisation is indicated with a dot written in between the salt molecule and the surrounding water molecules
45
What are anhydrous salts?
Anhydrous salts are those that have lost their water of crystallisation, usually by heating, in which the salt becomes dehydrated
46
Give the word equation for the dehydration of Hydrated Copper (II) Sulfate
Hydrated Copper (II) Sulfate ⇌ Anhydrous Copper (II) Sulfate + Water
47
What happens to anhydrous copper (II) sulfate crystals when they're added to water?
When anhydrous copper (II) sulfate crystals are added to water they turn blue and heat is given off (exothermic); this reaction is reversible
48
What happens when (now hydrated) copper (II) sulfate crystals are heated in a test tube?
When Copper (II) Sulfate crystals are heated in a test tube, the blue crystals turn into a white powder and a clear, colourless liquid (water) collects at the top of the test tube
49
Give the chemical equation for the dehydration of Hydrated Copper (II) Sulfate
CuSO4.5H2O (s) ⇌ CuSO4 (s) + 5H2O (l)
50
Give the word equation for the dehydration of Hydrated Cobalt (II) chloride
Hydrated Cobalt (II) Chloride ⇌ Anhydrous Cobalt (II) Chloride + Water
51
Give the chemical equation for the dehydration of Hydrated Cobalt (II) Chloride
CoCl2.6H2O (s) ⇌ CoCl2 (s) + 6H2O (l)
52
What happens to anhydrous blue cobalt(II) chloride crystals when they are added to water?
When anhydrous blue cobalt(II) chloride crystals are added to water they turn pink and the reaction is reversible
53
What happens to the the cobalt(II) chloride crystals when they are heated in a test tube?
When the cobalt(II) chloride crystals are heated in a test tube, the pink crystals turn back to the blue colour again as the water of crystallisation is lost
54
Why are the pink crystals know as hydrated cobalt (II) chloride?
The form of cobalt(II) chloride in the crystals that are pink is known as hydrated cobalt (II) chloride because it contains water of crystallisation
55
What does it mean if a reversible reaction is in a state of equilibrium?
When during the course of reaction, the rate of the forward reaction equals the rate of the reverse reaction, then the overall reaction is said to be in a state of equilibrium
56
How do the molecules behave in a reaction at equilibrium?
It is dynamic eg the molecules on the left and right of the equation are changing into each other by chemical reactions constantly and at the same rate
57
How does the concentration of reactants and products change in a reaction at equilibrium?
The concentration of reactants and products remains CONSTANT (given there is no other change to the system such as temperature and pressure)
58
In what conditions does a reaction reach equilibrium?
It only occurs in a closed system so that none of the participating chemical species are able to leave the reaction vessel
59
What does equilibrium position mean?
Equilibrium position refers to the relationship between the concentration of reactants and products at the equilibrium state
60
What does it mean When the position of equilibrium shifts to the left?
When the position of equilibrium shifts to the left, it means the concentration of reactant increases
61
What does it mean When the position of equilibrium shifts to the right?
When the position of equilibrium shifts to right, this means the concentration of product increases
62
What is a catalyst's effect on the position of the equilibrium?
The presence of a catalyst does not affect the position of equilibrium but it does increase the rate at which equilibrium is reached
63
Why does a catalyst increase the rate at which equilibrium is reached?
This is because the catalyst increases the rate of both the forward and backward reactions by the same amount (by providing an alternative pathway requiring lower activation energy) As a result, the concentration of reactants and products is nevertheless the same at equilibrium as it would be without the catalyst
64
What is Le Chatelier’s Principle ?
Le Chatelier’s Principle states that when a change is made to the conditions of a system at equilibrium, the system automatically moves to oppose the change.
65
How is Le Chatelier’s Principle used?
The principle is used to predict changes to the position of equilibrium when there are changes in temperature, pressure or concentration.
66
What is the effect of an increase in temperature on the position of the equilibrium?
Equilibrium moves in the endothermic direction to reverse the change
67
What is the effect of a decrease in temperature on the position of the equilibrium?
Equilibrium moves in the exothermic direction to reverse the change
68
What is the effect of an increase in pressure on the position of the equilibrium?
Equilibrium shifts in the direction that produces the smaller number of gaseous molecules to decrease the pressure again
69
What is the effect of an decrease in pressure on the position of the equilibrium?
Equilibrium shifts in the direction that produces the larger number of molecules of gas to increase the pressure again
70
What is the effect of an increase in concentration (of the reactant) on the position of the equilibrium?
Equilibrium shifts to the right to reduce the effect of increase in the concentration of a reactant
71
What is the effect of an decrease in concentration (of the reactant) on the position of the equilibrium?
Equilibrium shifts to the left to reduce the effect of a decrease in reactant (or an increase in the concentration of product)
72
What connects oxidation and reduction?
Oxidation and reduction take place together at the same time in the same reaction These are called redox reactions
73
What are 3 key things which define oxidation?
Oxygen is added to an element or a compound An element, ion or compound loses electrons The oxidation state of an element is increased
74
What are 3 key things which define reduction?
Oxygen is removed from an element or a compound An element, ion or compound gains electrons The oxidation state of an element is decreased
75
What is the oxidation state?
The oxidation state (also called oxidation number) is a number assigned to an atom or ion in a compound which indicates the degree of oxidation (or reduction)
76
What does the oxidation state help you do?
The oxidation state helps you to keep track of the movement of electrons in a redox process
77
How is the oxidation state shown?
It is written as a +/- sign followed by a number.
78
What does the oxidation number refer to?
Oxidation number refers to a single atom or ion only
79
What is the oxidation number of a compound?
The oxidation number of a compound is 0
80
What is the oxidation number of an element?
The oxidation number of an element is 0
81
What is the oxidation number of oxygen in a compound?
The oxidation number of oxygen in a compound is always -2 (except in peroxide R-O-O-R, where it is -1)
82
What are ionic equations and what do they show?
Ionic equations are used to show only the particles that actually take part in a reaction These equations show only the ions that change their status during a chemical process, i.e: their bonding or physical state changes
83
What are the other ions present in a reaction which are not involved called?
The other ions present are not involved and are called spectator ions
84
practice redox reactions
:-)
85
What is an oxidising agent?
A substance that oxidises another substance, in so doing becoming itself reduced
86
What are examples of an oxidising agent?
Common examples include hydrogen peroxide, fluorine and chlorine
87
What is a reducing agent?
A substance that reduces another substance, in so doing becoming itself oxidised
88
What are examples of. a reducing agent?
Common examples include carbon and hydrogen
89
Why is the process of reduction very important in the chemical industry?
The process of reduction is very important in the chemical industry as a means of extracting metals from their ores
90
How can redox reactions be identified?
Redox reactions can be identified by the changes in the oxidation states when a reactant goes to a product (or by colour changes)
91
What are two common examples of substances which can de identified as a redox reaction by their colour change?
Two common examples are acidified potassium manganate(VII), and potassium iodide
92
What is potassium manganate and when is it used?
Potassium manganate (VII), KMnO4, is an oxidising agent which is often used to test for the presence of reducing agents
93
What colour change is shown by potassium manganate when added to a reducing agent?
When acidified potassium manganate (VII) is added to a reducing agent its colour changes from pink-purple to colourless
94
What is potassium iodide and when is it used?
Potassium iodide, KI, is a reducing agent which is often used to test for the presence of oxidising agents
95
What colour change is shown by potassium iodide when added to an oxidising agent?
When added to an acidified solution of an oxidising agent such as aqueous chlorine or hydrogen peroxide, the solution turns a brown colour due to the formation of iodine

Chemistry IGCSE CIE Extended (15 decks)

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