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GCSE Chemistry > C8 - Rates & Equilibrium > Flashcards

C8 - Rates & Equilibrium Flashcards

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1
Q

What is activation energy?

A

The minimum energy needed for a reaction to take place

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2
Q

What is anhydrous?

A

Describes a substance that does not contain water

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3
Q

What is a catalyst?

A

A substance that speeds up a chemical reaction by providing a different pathway for the reaction that has a lower activation energy. The catalyst is chemically unchanged at the end of the reaction

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4
Q

What is climate change?

A

The change in global weather patterns that could be caused by excess greenhouse gases in the atmosphere

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5
Q

What is a closed system?

A

A system in which no matter enters or leaves

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6
Q

What is collision theory?

A

An explanation of chemical reactions in terms of reacting particles colliding with sufficient energy for a reaction to take place

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7
Q

What is equilibrium?

A

The point in a reversible reaction in a closed system at which the forward and backward rates of reaction are the same. Therefore, the concentration of products and reactants stay constant

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8
Q

What is hydrated?

A

describes a substance that contains water in its crystals

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9
Q

What is Le Châtelier’s principle?

A

When a change in conditions is introduced to a system at equilibrium, the position of equilibrium shifts so as to cancel out the change

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10
Q

What is precision?

A

A precise measurement is one in which there is very little spread about the mean value. Precision depends only on the extent of random errors - it gives no indication of how close results are to the true (accurate) value

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11
Q

What is a reversible reaction?

A

a reaction in which the products can re-form the reactants

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12
Q

What is the equation for mean rate of reaction?

A

Quantity of reactant used / time
OR
quantity of product formed / time

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13
Q

What are the units for mean rate of reaction?

A

g/s or cm³/s

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14
Q

What will happen to the rate of reaction if the mixture of reactants is constantly stirred and why?

A

The rate of reaction will increase, this is because stirring the mixture causes the reactant particles to gain more kinetic energy and there are therfore more collision between reactants. As a result there are more successful collisions and the rate of reaction increases

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15
Q

What will happen to the rate of reaction if 25cm³ of acid (one of the reactants) is replaced with 25cm³ of water and why?

A

The rate of reaction will decrease, this is because water may not react with the reactants and will therefore just get in the way and prevent collisions between reactant particles. Therefore, there will be less collisions between reactants and as a result fewer successful reactions. This causes the rate of reaction to decrease

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16
Q

What will happen to the rate of reaction if a strip of magnesium (one of the reactants) is folded twice and why?

A

The rate of reaction will decrease, this is because there is a smaller surface area and therefore there will be less frequent collisions between reactants, as a result there are fewer successful collisions and the rate of reaction decreases

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17
Q

What will happen to the rate of reaction if you half the volume of acid (one of the reactants) and why?

A

The rate of reaction will decrease, this is because there are fewer reactant particles and therefore less frequent collision, as a result there are less successful collisions and the rate of reaction decreases

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18
Q

What will happen to the rate of reaction if the reactant mixture is heated and why?

A

The rate of reaction will increase, this is because the reactant particles will have more kinetic energy and will collide and react with the other reactant particles more often. An increase in the number of collisions causes an increase in the number of successful collisions. Therefore the rate of reaction will increase

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19
Q

What is required for 2 reactants to have a successful collision?

A

They must collide with the correct orientation and with enough energy. Reactants with not enough energy or not facing the correct direction will not react and will just bounce against each other

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20
Q

calculate the mean rate of reaction if 40cm³ of hydrogen gas was formed in 10s

A

4 cm³/s

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21
Q

calculate the mean rate of reaction if 0.6g of carbon dioxide was formed in 20s

A

0.03g/s

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22
Q

calculate the mean rate of reaction if 0.05 moles of sulfur was formed in 30s

A

0.053 g/s

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23
Q

What can the rate of a chemical reaction be changed by?

A

changing the:

  • Concentration of solutions
  • Volume of gases
  • Surface area of solids
  • presence of a catalyst
  • temperature
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24
Q

Why is the rate of reaction fastest at the beginning of a reaction but then slow down?

A

At the beginning of the reaction, the container is full of reactants, however near the end of the reaction there are fewer reactants than products meaning it is less likely for there to be collisions, therefore reducing the number of successful collision and therefore the reaction slows down

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25
Q

Why is cotton wool placed at the top of a conical flask when investigating rate of reaction by mass loss (when there is a gaseous product)

A

The cotton wool is placed at the top to allow only gaseous products to escape and trap any solid/liquid reactants that my be carried by the gas

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26
Q

Why is calculating the rate of reaction by measuring mass loss not suitable when a product is hydrogen or other gases with a small relative formula mass?

A

The loss in mass may be too small to measure, making your results inaccurate

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27
Q

What are 2 ways of measuring the rate of reaction when there is a gaseous product?

A

1) Measure the mass loss, place cotton wool at the top of a conical flask, this allows the gaseous product to escape. Measure the mass loss at regular intervals and calculate the mean rate of reaction
2) Measure the volume of gas, either place a gas syringe at the top of the conical flask, or a pipe which leads into an upside down measuring cylinder full of water. Measure the volume of gas formed at regular intervals and calculate the mean rate of reaction

28
Q

Explain why the rate of reaction falls to 0 after a period of time.

A

After a period of time, all the reactants may have been used up and have formed products. This means the reaction stops as there are no more reactants to react with each other

29
Q

How does the concentration of reactants in solution effect the rate of reaction?

A

Increasing the concentration of reactants in a solution increases the number of particles per unit volume. This increases the frequency of collisions (but not the energy of collisions) between reactant particles and so the rate of reaction increases.

Doubling the concentration of reactants in a solution doubles the number of particles per unit volume. This doubles the frequency of collisions (but not the energy of collisions) between reactant particles and so the rate of reaction doubles.

30
Q

How does the pressure of reactant gases effect the rate of reaction?

A

Increasing the pressure of gaseous reactants increases the number of reactant particles per unit volume. This increases the frequency of collisions (but not the energy of collisions) between reactant particles and so the rate of reaction increases

Doubling the pressure of gaseous reactants doubles the number of reactant particles per unit volume. This doubles the frequency of collisions (but not the energy of collisions) between reactant particles and so the rate of reaction doubles.

31
Q

How does the pressure of reactant gases effect the rate of reaction?

A

Increasing the pressure of gaseous reactants increases the number of reactant particles per unit volume. This increases the frequency of collisions (but not the energy of collisions) between reactant particles and so the rate of reaction increases

32
Q

How does the size of particles effect the rate of reaction?

A

Decreasing the particle size of the same mass of solid reactants increases the surface area to volume ratio of the solid reactants. This increases the frequency of collisions (but not the energy of collisions) between reactant particles and so the rate of reaction increases

Halving the particle size of the same mass of solid reactants doubles the surface area to volume ratio of the solid reactants. This doubles the frequency of collisions (but not the energy of collisions) between reactant particles and so the rate of reaction doubles

33
Q

How does the temperature of reaction effect the rate of reaction?

A

Increasing the temperature of a reaction increases the frequency of collisions AND (more importantly) increases the energy of the collisions between reactant particles and so the rate of reaction increases.

Doubling the temperature of a reaction doubles the frequency of collisions AND (more importantly) increases the energy of the collisions between reactant particles and so the rate of reaction more than doubles

34
Q

Describe the method for investigating the effect of temperature on the rate of a reaction by using a reaction that causes turbidity

A

1) Measure out 50cm³ of the sodium thiosulfate solution into a 100cm³ conical flask
2) Place the conical flask containing the sodium thiosulfate on the cross
3) Measure out 10cm³ of hydrochloric acid into a beaker
4) Stir the sodium thiosulfate and record its temperature
5) Add the HCl to the sodium thiosulfate and immediately start timing
6) Stop timing when you can no longer see the cross through the mixture

35
Q

Describe the method for investigating the effect of concentration on the rate of a reaction by using a reaction that causes turbidity

A

1) Measure out 50cm³ of 40g/dm³ sodium thiosulfate solution into a 100cm³ conical flask
2) Place the conical flask containing the sodium thiosulfate on the cross
3) Measure out 10cm³ of 1mol/dm³ hydrochloric acid into a beaker
4) Stir the sodium thiosulfate and record its temperature
5) Add the HCl to the sodium thiosulfate and immediately start timing
6) Stop timing when you can no longer see the cross through the mixture
7) Repeat steps 1-6 three more times but decrease the concentration of sodium thiosulfate by 10g/dm³ each time. (Do this by mixing different volumes of water and sodium thiosulfate

36
Q

Why does the mixture go from transparent to opaque in the reaction between hydrochloric acid and sodium thiosulfate solution?

A

One of the products of the solution is a fine precipitate of sulfur. This is insoluble and makes the solution appear cloudy, this eventually makes the solution opaque

37
Q

Describe the method for investigating how concentration affects rate of reaction

A

1) Prepare 20cm³ of 0.4 mol/dm³ hydrochloric acid by mixing 4 cm³ of 2.0 mol/dm³ HCl with 16cm³ of water in a boiling tube using measuring cylinders
2) Place the boiling tube in a rack
3) Set up a gas syringe by using a stand and clamp
4) Cut a 3cm length of magnesium ribbon and rub down with emery paper
5) Add the magnesium ribbon to the hydrochloric acid, attaching the delivery tube straight away and starting the timer
6) Record the volume of gas formed in 20 seconds
7) Repeat the experiment with different concentrations of HCl and using a new strip of magnesium
8) Repeat the whole experiment 2 more times and get a mean average for each result

38
Q

What is zero-point error?

A

Zero point error is when a system gives a false reading when the true value of a measured quantity is 0. Zero-point error is a systematic error as it is an error from the instrument being used to measure it

39
Q

How can the direction of a reversible reaction be changed?

A

By changing the conditions

40
Q

What happens during a reversible reaction?

A

The products of the forward reaction can react to form the original reactants

41
Q

What is the difference between the forward and backwards reaction in a reversible reaction?

A

In a reversible reaction, one direction will be exothermic, whilst the other will be endothermic. The bond energy will be the same for both directions (However the exothermic direction will be negative and the endothermic direction will be positive)

42
Q

What happens if you change the conditions of a reversible reaction at equilibrium?

A

The point of equilibrium and therefore the relative amounts of products and reactants will change

43
Q

What is the effect of changing the concentration on a reversible reaction at equilibrium?

A

If the concentration of one of the reactants or products is changed, the system will no longer be at equilibrium and the concentrations of all the substances will change until equilibrium is reached again.

If the concentration of a reactant is increased, more products will be formed until equilibrium is reached again.

If the concentration of a product is increased, more reactants will be formed until equilibrium is reached again.

44
Q

What happens if you increase the concentration of reactants in a reversible reaction at equilibrium?

A

More products will be formed until equilibrium is reached again

45
Q

What happens if you increase the concentration of products in a reversible reaction at equilibrium?

A

More reactants will be formed until equilibrium is reached again

46
Q

What happens if the temperature of a system at equilibrium is increased?

A

The reaction will move in the endothermic direction:

  • The relative amounts of products (yield) at equilibrium increases for an endothermic reaction
  • The relative amounts of products (yield) at equilibrium decreases for an exothermic reaction
47
Q

What happens if the temperature of a system at equilibrium is decreased?

A

The reaction will move in the exothermic direction:

  • The relative amounts of products (yield) at equilibrium decreases for an endothermic reaction
  • The relative amounts of products (yield) at equilibrium increases for an exothermic reaction
48
Q

What is the effect of changing the pressure on a reversible reaction at equilibrium?

A

For gaseous products at equilibrium:

  • An increase in pressure causes the equilibrium position to shift towards the side with the smaller number of molecules (as shown by the symbol equation for that reaction)
  • A decrease in pressure causes the equilibrium position to shift towards the side with the larger number of molecules (as shown by the symbol equation for that reaction)
49
Q

What happens if you increase the pressure on a reversible reaction at equilibrium?

A

The equilibrium position will shift towards the side with the smaller number of molecules

50
Q

What happens if you decrease the pressure on a reversible reaction at equilibrium?

A

The equilibrium position will shift towards the side with the larger number of particles

51
Q

What does it mean if the position of equilibrium shifts to the left?

A

If the point of equilibrium is shifted to the left, more reactants will be formed

52
Q

What does it mean if the position of equilibrium shifts to the right?

A

More products will be formed

53
Q

Explain in detail what happens to the equilibrium mixture when more water is added in the equation:
Co(H₂O)₆²⁺ + 4Cl⁻ ⇌ CoCl₄²⁻ + 6H₂O

A

The concentration of the products has increased, to counteract the change more reactants are formed (the equilibrium point moves to the left) to use up the excess products.

54
Q

Explain in detail what happens to the equilibrium mixture when the temperature of the mixture is decreased in the equation:
Co(H₂O)₆²⁺ + 4Cl⁻ ⇌ CoCl₄²⁻ + 6H₂O
(Endothermic in forward direction)

A

When the temperature of the mixture is decreased, the temperature of the surroundings decreases. As a result the reaction moves in the exothermic direction to heat up the surroundings. Therefore more of the original reactants are formed

55
Q

What has a greater effect on the rate of a chemical reaction, increased energy or increased collision?

A

Increased energy has a greater effect on the rate of reaction than an increased frequency of collisions as there are a greater number of particles exceeding the activation energy

56
Q

What are the 3 ways of measuring the rate of reaction?

A
  • Measuring mass loss
  • Measuring the increasing volume of gas given off
  • Measuring the decreasing light passing through a solution
57
Q

How do you calculate the rate of reaction at a specific time in a reaction from a graph?

A

Draw a tangent to the curve at the specific time. Calculate the gradient of the tangent.

58
Q

What factors can change the rate of reaction?

A

Temperature, Concentration, Pressure, Surface area, Catalysts

59
Q

What increases the rate of reaction?

A
  • Increase the frequency of reacting particles colliding with each other
  • Increase the energy that they have when they collide
60
Q

What are the advantages of catalysts in the Haber Process?

A
  • Although the catalysts themselves can be very costly (i.e. gold or platinum), it is cheaper to use a catalyst to increase the rate of reaction than to pay for the extra energy needed without one. The catalysts are also not used up meaning that you only need to buy them once
  • Catalysts also help save the environment and combat climate change. This is because the extra energy needed without catalysts is often produced by burning fossil fuels. This prevents more greenhouse gases entering the atmosphere and helps combat climate change
61
Q

What is an example of a reversible reaction?

A

Hydrated copper sulfate (blue) ⇌ anhydrous copper sulfate (white) + water
CuSO₄.5H₂O ⇌ CuSO₄ + 5H₂O

62
Q

Explain why the solution becomes cloudy in the reaction between “sodium thiosulfate solutiom and dilute hydrochloric acid”

A

After the reaction is complete, there is a very fine precipitate of sulfur left in the container. This mixes with the water and sodium chloride, causing it to become cloudy

63
Q

The reaction “2H₂S(g) + 3O₂(g) -> 2H₂O(g) + 2SO₂(g)” is an exothermic reaction, draw the reaction profile for this reaction

A
64
Q

The reaction “2H₂S(g) + 3O₂(g) -> 2H₂O(g) + 2SO₂(g)” is an endothermic reaction, draw the reaction profile for this reaction

A
65
Q

What is the error with the apparatus in the diagram?

A

The delivery tube is in the liquid, it should not be in the liquid

66
Q

What 2 pieces of equipment do you need to find the rate of production of hydrogen gas?

A
  • Gas syringe

* Stopwatch

GCSE Chemistry (15 decks)

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