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AQA GCSE Chemistry > rates of reaction > Flashcards

rates of reaction Flashcards

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1
Q

Define Rate of Reaction:

A

The speed at which a reaction occurs - the olume of gas made/lost per second

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2
Q

What is activation energy?

A

The minimum amount of energy with which particles must frequently collide for a reaction to take place

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3
Q

What factors affect the rate of reaction?

A
  • temperature
  • pressure/concentration
  • surface area of reactant
  • presence of a catalyst
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4
Q

What is the relationship between temperature and the rate of a reaction?

A

Increasing the temperature, increases the rate of reaction

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5
Q

Why is the relationship between temperature and the rate of reaction like so?

A
  • increasing the temperature
  • means the particles have more kinetic energy
  • so collide more frequently at a level above the activation energy
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6
Q

What is the relationship between pressure/concentration and the rate of a reaction?

A

Increasing the pressure of the gas/ concentration of the solution, increases the rate of reaction

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7
Q

Why is the relationship between pressure and the rate of reaction like so?

A
  • increasing the pressure
  • means particles are closer together
  • so collide more frequently at a level above the activation energy
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8
Q

Why is the relationship between concentration and the rate of reaction like so?

A
  • increasing the concentration
  • increases the number of particles per unit volume
  • meaning there are more frequent collisions between particles at a level above their activation energy
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9
Q

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

A

increasing the surface area, increases the rate of reaction

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10
Q

Why is the reationship between surface area and the rate of a reaction like so?

A
  • increasing the surface area
  • means more particles are exposed on the surface to collide with particles in the other reactant
  • meaning more frequent collisions between particles at a level above their activation energy
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11
Q

What is the relationship between a catalyst and the rate of a reaction?

A

adding a catalyst, increases the rate of reaction

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12
Q

Why is the relationship between a catalyst and the rate of a reaction like so?

A
  • adding a catalyst
  • lowers the activation energy required for the particles to collide with
  • so there are more frequent collisions between particles at a level above their activation energy
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13
Q

How do you calculate the rate of a reaction?

A

quantity of reactant used/ time taken

quantity of product formed/time taken

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14
Q

Describe the required practical investigating the effect of concentration on the rate of reaction:

A

1) Using a measuring cylinder, put 10 of sodium thiosulphate into a conical flask and ass 40 of water using a measuring cylinder. Place the conical flask on a black cross
2) Put 10 of HCl in a measuring cylinder and add it to the flask, starting a stopwatch at the same time. Ensure the flask is continuously swirled
3) Look from directly above the flask and stop the clock when you can no longer see the cross
4) Record this time
5) Repeat the process but vary the volume of sodium thiosulphate and water to produce different concentrations
6) repeat the whole process at least twice more to calculate a mean time at each concentration

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15
Q

What are the key things to be aware of with the equpment for a water displacement test?

A
  • there is a bung to prevent gas escaping
  • there are graduation marks on the measuring cylinder
  • water fills to the top of the cylinder at the start
  • the end of the deliver tube goes into the measuring cylinder
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16
Q

What is the main error when using Mg as the reactant with HCl in a water displacement experiment? How can this be fixed?

A

The hydrogen gas produced by the reacction can dissolve in the water so a gas syringe should be used

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17
Q

What are the observations of a reaction between HCl and Mg or CaCO3?

A
  • bubbles of gas

- Mg or CaCO3 dissolves

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18
Q

What is the dependent and inderpendent varibale in a water displacement experiment?

A
  • dependent = volume of gas

- independent = temperature of HCl

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19
Q

In a loss of mass experiment, what must be added into the conical flask and why?

A

Cotton wool must be placed in the neck of the conical flask to allow the gas to escape but also preventing the build up of pressure which would occur with a bung

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20
Q

What is the dependent and independent variable in a loss of mass experiment?

A
  • independent = surface area

- dependent = mass lost

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21
Q

What is a turbidity experiment?

A

When a solution creates a precipitate and reduces your ability to see through the solution

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22
Q

What is a precipitate?

A

A solid formed from the reaction of two liquids

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23
Q

What safety measures are needed in a turbidity reaction between sodium thiosulphate and HCl?

A
  • opening windows for good ventilation for the acidic sulfur dioxide
  • using an alkali stop bath solution
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24
Q

What are the common errors associated with the turbidity reaction?

A
  • timing errors (inconsistent start time)
  • not looking directly down at the cross
  • not swirling
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25
Q

How does a catalyst increase the rate of a reaction?

A
  • lowers the activation energy required

- by providing an alternative pathway

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26
Q

What is the relationship between concentration and volume of gas produced?

A

Doubling the conc, doubles the vol of gas produced

27
Q

How can we tell what the limiting reagent in a reaction is?

A
  • one who’s moles are less in the reaction than the ration dictates it should be
  • find the mol ratio
  • than calculate what the ratio should be
  • bring the mol ratio to e.g. 2:2 and whatever is lower, is the limiting reagent
28
Q

What happens to hydrated copper sulfate solution when heated?

A

It decomposes into anhydrous copper sulfate and water

29
Q

What colour is copper sulfate solution?

A

Blue

30
Q

What colour is anyhdrous copper sulfate?

A

white

31
Q

How is the hydrated copper sulfate reaction reversed?

A

By adding water

32
Q

What is the rule of dynamic equilibrium?

A

In a closed system:

  • the forward and reverse reactions are taking place at the same rate
  • so the concentration of the reactants and products stays the same
33
Q

What is Le Chatlier’s principle?

A

If a change is made to the conditions of a system at equilibrium, the position of the equilibrium will shift to oppose the change in conditions

34
Q

What is the reaction in the haber process?

A

nitrogen + hydrogen = ammonia

35
Q

What are the conditions with which the haber process takes place?

A
  • with an iron catalyst
  • at 450 degrees
  • at 200atm pressure
36
Q

What is ammonia chemically?

A

A weak base (proton acceptor)

37
Q

Why must fertilisers be soluble?

A

So they can dissolve in water and be absorbed by root hair cells

38
Q

What type of mixture is a fertiliser?

A

a formulation

39
Q

What are the contents of a fertiliser?

A
  • either ammonium ions or nitrate ions (for soluble nitrogen)
  • phosphate ions (soluble phosphorus)
  • any potassium compound
40
Q

Why can any potassium compound be used in a fertiliser?

A

Because they all dissolve in water to produce potassium ions

41
Q

What type of reaction can ammonia undergo to make ammonium ions?

A

neutralisation with nitric acid

42
Q

What is the product of ammonia and nitric acid?

A

ammonium nitrate salt

43
Q

What type of reaction can ammonia undergo to make nitrate ions?

A

oxidation

44
Q

How are potassium ions obtained for fertilisers?

A

potassium chloride or potassium sulfate is mined from the ground

45
Q

Why can’t phosphate rock, unlike potassium, be used as a fertiliser?

A

It is insoluble

46
Q

What are the three different reactants which can be used with phosphate rock?

A
  • nitric acid
  • sulfuric acid
  • phosphoric acid
47
Q

What are the products of phosphate rock and nitric acid?

A

calcium nitrate and phosphoric acid

48
Q

What is done with the phosphoric acid from the reaction between phosphate rock and nitric acid?

A

neutralised with ammonia to produce ammonium phosphate

49
Q

what is the product of the reaction between phosphate rock and sulfuric acid?

A

a single superphosphate which contains calcium phosphate and calcium sulfate

50
Q

What is the product of the reaction between phosphate rock and phosphoric acid?

A

a triple superphosphate (calcium phosphate)

51
Q

What is the effect on a catalyst on equilibrium? Why?

A
  • there is no effect

- as the catalyst speeds up both the forward and reverse reactions equally

52
Q

What is the effect of increasing the concentration of the reactants on equilibrium? Why?

A

Equilibrium shifts to the right (forward) to oppose the increase in the concentration of the reactants. More of the extra reactants thus get used up to make products

53
Q

What is the effect of decreasing the concentration of the reactants on equilibrium? Why?

A

Equilibrium shifts to the left to oppose the decrease in the concentration of reactants. Removed reactants must be replaced by the product breaking down

54
Q

What is the effect of increasing the concentration of the products on equilibrium? Why?

A

Equilibrium shifts to the left to oppose the increase in the concentration of the products. The product breaks down to form more reactants, reducing the amount of the product present

55
Q

What is the effect of decreasing the concentration of the products on equilibrium? Why?

A

Equilibrium shifts to the right to oppose the decrease in the concentration of the products. There is less product so the reactants will react more to form more product

56
Q

What is the effect of increasing the pressure on equilibrium? Why?

A

The equilibrium is shifted to the side of the reaction which has less molecules to oppose this increase in pressure so the pressure reduces

57
Q

What is the effect of decreasing the pressure on equilibrium? Why?

A

The equilibrium is shifted to the side which has more molecules to oppose the decrease in pressure by increasing it

58
Q

When does changing the pressure have no affect on equilibrium?

A

When there are equal numbers of molecules in the reactants and products

59
Q

What is the effect of increasing the temperature on equilibrium? Why?

A

The equilibrium is shifted in the direction of the reaction (forward or backward) which is endothermic, in order to cool the environment down, opposing the temperature increase

60
Q

What is the effect of decreasing the temperature on equilibrium? Why?

A

The equilibrium is shifted in the direction of the reaction (forward or backward) which is exothermic, in order to warm the environment up, opposing the temperature decrease

61
Q

Why is the temperature chosen for the Haber process 450 degrees?

A
  • Lowering the temperature, will increase the yield of ammonia as the equilibrium shift right as the forward reaction is exothermic, so the temperature decrease is opposed
  • But increasing the temperature, increases the rate of reaction as particles have more kinetic energy so collide more frequently and with greater energy
  • so therefore 450 degrees is a compromise temperature
  • meaning it is a balance between the temperature cool enough for equilibrium but warm enough for rate of reaction
62
Q

Why is the low conversion of products to ammonia in the Haber process not a big problem?

A

since the unreacted reactants are recycled and reacted again to make more ammonia

63
Q

How is ammonia separated out of the Haber process?

A

the mixture is cooled enough so the ammonia condenses and the liquid is drained out the system whereas the gaseous nitrogen and hydrogen are kept within the system and recycled

64
Q

Define the term equilibrium:

A
  • The rate of the forward reaction is equal to the rate of the backward reaction
  • so the concentrations of reactants and products do not change

AQA GCSE Chemistry (10 decks)

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