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GCSE Chemistry > C8 - Rates and Equilibrium > Flashcards

C8 - Rates and Equilibrium Flashcards

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1
Q

What does the rate of a chemical reaction tell us?

A

The rate of a chemical reaction tells us how fast reactants turn into products

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2
Q

Why is the rate of chemical reactions important in humans and also in the chemical industry?

A

In the human body:
-Respiration

In the chemical industry:

  • Efficiency
  • Profit
  • Safety
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3
Q

What are the 2 ways you can find out the rate of a chemical reaction?

A

1) Measuring the rate the reactants are used up

2) Measuring the rate the products are made

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4
Q

What are the 3 techniques used to collect data on the rate of reactions?

A

1) Measuring the decreasing mass of a reaction mixture.
- If the reaction gives off a gas, the mass will decrease as gas moves into the surroundings.

2) Measuring the increasing volume of gas given off.
- You can collect the gas in a gas syringe.

3) Measuring the decreasing light passing through a solution.
- Some reactions produce an insoluble solid precipitate which makes the solution go cloudy.

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5
Q

For each of the 3 techniques, what will the graph look like?

A

1) Decreasing mass = decreasing curve followed by plateau as the limiting reactant is used up.
2) Increasing gas volume = increasing curve followed by plateau.
3) Decreasing light passing through = decreasing curve followed by plateau as the reaction finishes.

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6
Q

What does the gradient of a line for such an experiment at any given point tell us?

A

The rate of reaction.

steeper gradient = faster rate

The rate of a reaction usually slows as the limiting reactant (reactant that gets used up first) is used up.

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7
Q

How do you calculate the gradient at any given point of a curve?

A

Draw a tangent to the curve

m = Δy / Δx

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8
Q

How do you calculate the mean rate of a reaction?

A

You can use the formula:

Mean rate of reaction = quantity of reactant used (final mass - initial mass) / time

OR

Quanity of product formed / time

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9
Q

What is collision theory?

A

The theory that explains that reactions can only take place when the particles of reactants collide with a certain amount of energy.

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10
Q

What is the minimum amount of energy particles must have before they can react called?

A

The activation energy

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11
Q

Based on collision theory, reactions are more likely to happen if you?

A

1) Increase the frequency of reacting particles colliding with each other.
2) Increase the energy they have when they collide.

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12
Q

What does increasing the chance of a reaction occuring also increase?

A

The rate of the reaction

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13
Q

How does surface area affect reaction rate?

A

By increasing the surface area of the reactants in solution, you increase the number of collisions.

Therefore, according to collision theory, the rate of the reaction is increased.

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14
Q

What would have a faster rate of reaction in a HCL solution, marble chips or marble powder?

Marble = CaCO3

A

By refining the marble into marble powder, a larger surface area is created. Therefore the SA: V ratio is increased and more collisions occur. The reaction happens quicker.

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15
Q

What happens to the rate of reaction when you increase the temperature?

A

It increases.

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16
Q

According to collision theory, why does the rate of reaction increase with increased temperature?

A
  • Particles collide more often (because they move faster).

- Collide with more energy.

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17
Q

Why do particles collide with more energy when the temperature is increased?

A

As the particles heat up, they move faster. Therefore, when they collide, they will collide with more energy. (A bit like bumping into someone when you are running compared to walking).

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18
Q

What has a greater effect on rate of reaction, Frequent Collisions or Particles Exceeding the Activation Energy?

A

An increased proportion of particles exceeding the activation energy has a greater effect on rate than increased frequency of collisions.

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19
Q

What is the general rule of thumb for rate of reaction when you increase the temperature of a reaction by 10°C from room temperature?

A

The rate of reaction roughly doubles.

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20
Q

How would the effect of temperature on rate of reaction look on a graph?

A

It would show that the higher the temperature, the faster the reaction would finish.

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21
Q

How do fridges and freezers slow down the rate of reaction?

A

By reducing the temperature, fridges and freezes slow down the rate of the reactions that make food go off.

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22
Q

Why have some of the most beautiful buildings and statues made of limestone (CaCO3) starting to crumble at an increased rate?

A

Calcium Carbonate (CaCO3) reacts with acid. Because the concentration of acids in rainwater has risen in recent years, the rate of reaction has increased and the statues/buildings are crumbling at a faster rate.

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23
Q

How does increased concentration of reactants effect the rate of reaction?

A

It increases the rate of reaction.

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24
Q

Why does increased concentration increase the rate of reaction?

A

There are more particles moving around in the same volume of solution. Therefore, the particles are ‘more crowded’ and will collide more frequently. This increases the rate of reaction.

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25
Q

What is pressure?

A

Pressure is a measure of how much force is exerted on an area.

P = F / A (solid/gas) OR P = hρg (liquid)

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26
Q

How does increased pressure of reacting gases effect rate of reaction?

A

Increased pressure of reacting gases increases the rate of reaction.

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27
Q

Why does increased pressure of reacting gases increase the rate of reaction?

A

The gas particles are squashed more closely together. This increases the chance they will collide. Therefore increasing the rate of reaction.

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28
Q

What is the aim of RP5 - Investigating the effect of concentration on rate of reaction?

A

To investigate how changing the concentration of a solution affect rates of reaction.

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29
Q

What are the 2 methods for? What do they involve? How do they work?

A

Method 1: You have a set volume of HCl (10cm^3) which remains constant throughout. The other reactant is the 50cm^3 of Sodium Thiosulfate (Na2S2O3) which starts in the conical flask. (Total reaction volume = 60cm^3). Each time you reduce the amount of Na2S2O3 and replace it with water to dilute the Na2S2O3 but keep the total reaction volume the same (60cm^3). The reaction produces sulfur which covers the laminated X. You are timing how long it takes for the laminated X under the conical flask to disappear each time.

Method 2: You are going to be using 2 set volumes of different concentrations of acid. 1mol/dm^3 of HCl and 2mol/dm^3 of HCl. You will place a magnesium strip/ribbon in the acid. Mg + HCl produces MgCl and Hydrogen gas. You are going to collect the H2 gas produced in a measuring cylinder with water in it. Record how much gas is produced at set intervals for 100 seconds. Repeat with the other concentration of acid. A delivery tube and seal are needed - the tube must not touch the solution.

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30
Q

What is the conclusion for both RP5 methods?

A

The greater the concentration the greater the rate of a chemical reaction.

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31
Q

What is a catalyst?

A

A catalyst is a substance that speeds up the rate of a chemical reaction without itself being used up.

32
Q

Is a catalyst used up itself in a chemical reaction?

A

No, catalysts do not change a reaction, they speed up the same slower reaction.

mass of catalyst before reaction = mass of catalyst after reaction

33
Q

How do catalysts work to speed up reactions?

A

Catalysts work by providing an alternative reaction pathway that needs less activation energy.

Reaction profile with catalyst - the spike would be less steep.

34
Q

How does offering an alternative reaction pathway increase the rate of a chemical reaction?

A

Because activation energy is lower, more reactant particles have enough energy to react, so the reaction occurs faster.

35
Q

How does using a catalyst save energy costs in industry?

A

Less activation energy is needed so less money is needed to for example heat the reactants to a higher temperature so they can react.

This is why catalysts are very expensive but cost effective.

36
Q

What are some examples of catalysts?

A

A lot of catalysts are transition metal compounds.

Common catalysts include:

  • MnO2 - Manganese Dioxide
  • Catalase
  • KI - Potassium Iodide

The decomposition of Hydroyen Peroxide (2H2O2) is sped up using catalase.

37
Q

What are Reversible reactions?

A

Reactions where the products can be reacted to make the original reactants.

38
Q

What symbol is used to show a reversible reaction?

A

⇌

39
Q

Most chemical reactions are structured: A+B —> C+D? How are reversible reactions structured?

A

A+B⇌C+D, where A+B are the reactants.

OR

C+D⇌A+B, where C+D are the reactants.

40
Q

What are 4 examples of Reversible Reactions?

A

1) Hydrated copper (II) sulfate* ⇌ anhydrous copper (II) sulfate* + water

Hydrate copper (II) sulfate = blue
Anhydrous copper (II) sulfate = white
  • if you add water to the white anhydrous (dry) copper, it turns blue (lab test for water).
  • if you heat the hydrated copper, it turns into a white powder and drives off the water.

2) Ammonium chloride ⇌ ammonia + hydrogen chloride
3) Litmus paper - add alkali it turns blue by losing a H+ ion. If you add more acid, it changes back to red, by gaining a H+ ion.
4) The Haber Process

41
Q

What are the 2 diagnostic lab tests for water, H2O?

A

1) White anydrous copper sulfate turns blue.

2) Blue cobalt chloride paper turns pink.

42
Q

In a reversible reaction, one reaction is ________ and the other is _________.

A

One reaction is exothermic and the other is endothermic.

E.g A+B ⇌ C+D

If A+B are exothermic, than C+D is endothermic.

43
Q

How does the amount of energy transferred compare for a reaction in reverse?

A

It will transfer exactly the same amount of energy, but in the other direction.

Law of conservation of energy!

44
Q

How might a reversible reaction look on a reaction profile?

A

Exothermic reaction - reactant line higher up as energy is released.
Endothermic reaction - product line higher up as energy is taken in.

45
Q

How does the rate of a forwards reaction compare to the rate of the reverse reaction in a closed system, when at equilibrium?

A

At equilibrium in a closed system (no chemicals go in or out), the rate of the forward reaction equals the rate of the reverse reaction.

46
Q

What is meant by the term ‘dynamic equilibrium’?

A

Dynamic equilibrium refers to how forwards and reverse reactions continuously take place and are at the SAME RATE in a closed system.

47
Q

Describe how dynamic equilibrium is reached in a reversible reaction in a closed system?

A

1) A+B reacted
2) At first, C+D is produced at a slower rate than A+B.
3) Gradually the rate of C+D increases as the rate of A+B slows down.
4) Eventually the rates are the same in both directions of the reversible reaction.

48
Q

What metaphor can be used to describe dynamic equilibrium?

A

Going up a downward escalator. The rate of the escalator going down is the same as the person going up if at equilibrium.

49
Q

Why did scientists previously believe that a reversible reaction in a closed system stops, rather than continuing in dynamic equilibrium?

A

Because the masses of the susbstances weren’t changing, they assumed that the reaction had stopped.

50
Q

What does a dynamic equilibrium graph show?

A 
x-axis = time
y-axis = rate of reaction

It looks like a simplified drawing of the Eiffel Tower with the base on the y-axis.

One line for the forward curving downwards. Another line for the reverse reaction curving upwards, until they meet at the equilibrium point.

51
Q

What does La Châtalier’s principle state?

A

If a change is made to the *conditions of a system at equilibrium, the position of equilibrium shifts as to cancel out the change and restore equilibrium.

*Conditions changing could be pressure, temperature and concentration.

52
Q

How would you temporarily speed up the forwards reaction of the reaction below to generate more ICl3 product? Why does this happen?

ICl + Cl2 ⇌ ICl3

A

You would pump more chlorine in to increase the rate of iodine trichloride being produced.

Why:
According to La Châtelier’s Principle, by adding more Cl2, the reaction will temporarily shift in favour of the forwards reaction to restore dynamic equilibrium, whence more ICl3 would be made.

53
Q

What are the 2 ways which you can alter the conditions of a reversible reaction in dynamic equilibrium?

A

1) Altering the pressure

2) Altering the temperature

54
Q

What does increasing or decreasing the pressure of a reversible reaction do?

A

Increasing P - Shifts the reaction in favour of the reaction that forms fewer gas molecules.

Decreasing P - shifts the reaction in favour of the reaction that forms the greater number of gas molecules.

55
Q

What would happen if you increased the pressure of:

2NO2 ⇌ N2O4

A

There are more moles of gas on the left hand side.

The reaction shifts to the right to produce more lower pressure gas to bring it back to equilibrium. So the rate of the forwards reaction increases (more N2O4).

56
Q

What would happen if you decreased the pressure of:

2NO2 ⇌ N2O4

A

There are less moles of gas on the right hand side.

The reaction shifts to the left to produce more higher pressure gas molecules, to bring it back to equilibrium. So the rate of the reverse reaction increases (more 2NO2).

57
Q

What would happen if you increased the temperature of:

2NO2 ⇌ N2O4

  • forwards reaction is exothermic
  • reverse reaction is endothermic
A

The reactions shifts in favour of the reverse endothermic reaction to bring the temperature back down again.

So more NO2 gas is produced.

58
Q

What would happen if you decreased the temperature of:

2NO2 ⇌ N2O4

  • forwards reaction is exothermic
  • reverse reaction is endothermic
A

The reactions shifts in favour of the forwards exothermic reaction to bring the temperature back up again.

So more N2O4 gas is produced.

59
Q

What would happen if you altered the pressure of:

H2 + I2 ⇌ 2HI

A

The number of moles of gas is the same on both sides. So altering the pressure would have no effect on the products produced.

60
Q

What is the Haber process?

A

The Haber process is a process invented by german chemist Fritz Haber.

The process involves a reversible reaction which produces ammonia.

61
Q

Why is ammonia an important chemical?

A

It is really important for making fertilisers.

62
Q

What is the overall word and chemical equation of the Haber process?

A

Nitrogen + Hydrogen (iron catalyst) ⇌ ammonia

N2(g) + 3H2(g) ⇌ 2NH3 (g)

1:3:2 molar ratio

63
Q

At what temperature and atmospheric pressure does the Haber process need to be under?

A

450°C and 200 atmospheric pressure

64
Q

How is Nitrogen gas and Hydrogen gas collected for the Haber process?

A
  • Nitrogen is extracted from the air by being liquefied - heavily cooled.
  • Hydrogen is obtained from natural gas (methane).

Methane gas is reacted with steam to get hydrogen and carbon monoxide (bi-product).

65
Q

How is ammonia collected in liquid form after ammonia gas has been formed?

A

The reaction mixture is cooled so that the ammonia gas can liquify.

66
Q

What happens to the unreacted hydrogen and nitrogen?

A

It is recycled back into the reaction vessel.

67
Q

What type of reactions (energy-wise) are the forwards and reverse reactions in the Haber process?

A 
Forwards = Exothermic
Reverse = Endothermic
68
Q

Why is a pressure of 200 atmospheres needed in the Haber process?

A

N2 + 3H2 = 4 moles
2NH3 = 2 moles

A high pressure (200 atmospheres) is needed to shift the reaction to favour the forwards reaction (where there are less moles).

THIS PRODUCES MORE AMMONIA - MORE ECONOMIC £££

69
Q

Why is the moderately high temperature of 450°C needed for the Haber process?

A

If the temperature is too high - the reaction will shift in favour of the reverse reaction and less ammonia will be produced.

Likewise, if the temperature is too low, the rate of reaction will decrease.

Therefore, 450°C is a ‘compromised’ condition as it enables good ammonia production and a fast rate of reaction.

70
Q

Why is an iron catalyst necessary in the Haber process?

A

To speed up the rate of the reaction whilst not being itself used up.

71
Q

What 3 key fertilisers is ammonia used to make in a Lab?

A

1) Ammonium nitrate salt fertiliser
2) Ammonium sulfate salt fertiliser
3) Ammonium phosphate salt fertiliser

72
Q

What is the word and chemical equation for making ammonium nitrate salt fertiliser?

A

Ammonia + Nitric Acid —> Ammonium Nitrate + Water

NH3 (aq) + HNO3 (aq) —> NH4NO3 (aq)

73
Q

What is the word and chemical equation for making ammonium sulfate salt fertiliser?

A

Ammonia + Sulfuric Acid —> Ammonium Sulfate + water

2NH3 (aq) + H2SO4 (aq) —> (NH4)2 SO4 (aq)

74
Q

What is the word and chemical equation for making ammonium phosphate salt fertiliser?

A

Ammonia + Phosphuric Acid —> Ammonium Phosphate + water

3NH3 (aq) + H3PO4 (aq) —> (NH4)3 PO4 (aq)

75
Q

What type of reactions are the ammonium salt fertilisers examples of?

A

Neutralisation reactions between an acid and an alkali (ammonia).

Acid + Alkali —> Salt + Water (AAWS)

76
Q

How would crystals of the ammonium salt be extracted?

A

The aqueous solution would be gently heated to slowly evaporate the water and crystallise the salt.

77
Q

What method is carefully used to react the ammonia with the right amount of acid?

A

Titration

GCSE Chemistry (17 decks)

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