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A Level Chemistry > Module 3: Chapter 10 - Reactions Rates and Equilibrium > Flashcards

Module 3: Chapter 10 - Reactions Rates and Equilibrium Flashcards

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1
Q

What is the rate of reaction?

A

The rate of a chemical reaction is the change in concentration of a reactant or a product in a given time

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2
Q

What is the equation for rate of reaction?

A

Rate = Δconcentration / time

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3
Q

What are the units for rate of reaction?

A

mol dm⁻³ s⁻¹

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4
Q

When is the rate of reaction greatest?

A

At the start of the reaction as each reactant is at its highest concentration

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5
Q

Why does the rate of reaction slow as the reaction progresses?

A

The rate of reaction slows as the reaction progresses as the reactants are being used up, therefore there concentrations decrease

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6
Q

When does a reaction stop completely?

A

A reaction completely stops when one of the reactants has been completely used up, therefore the concentrations stop changing and the rate of reaction is 0

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7
Q

What factors affect the rate of a chemical reaction?

A
  • Concentration
  • Pressure
  • Temperature
  • Catalyst
  • Surface area of solid reactants
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8
Q

What is collision theory?

A

Collision theory states that 2 reacting particles must collide for a reaction to occur, and must be in the correct orientation and have sufficient energy to overcome the activation energy of the reaction

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9
Q

How does concentration affect the rate of reaction?

A

When the concentration of reactants is increased, the rate of reaction increases. This is because an increase in concentration increases the number of particles in the same volume. Therefore, the particles are closer together and will collide more frequently, therefore there will be more effective collisions (correct orientation and sufficient energy) and therefore an increased rate of reaction

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10
Q

How does pressure affect the rate of reaction?

A

When the pressure of a gas in increased, the concentration of gas molecules in a given volume increases. Therefore the gas molecules are closer together and collide more frequently, leading to more effective collisions in the same time, leading to a greater rate of reaction

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11
Q

What are the 2 ways to monitor the progress of a chemical reaction?

A
  • Monitoring the decrease in concentration of a reactant
  • Monitoring the increase in concentration of a product
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12
Q

What are the 2 methods to determine the rate of reaction with a gaseous product?

A
  • Monitoring the volume of gas produced at regular time intervals using gas collection
  • Monitoring the loss of mass of reactants using a mass balance
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13
Q

How would you determine the rate of reaction by monitoring the volume of gas produced?

A
  1. Set up the apparatus either using an upside down measuing cylinder in a water bath or a gas syringe
  2. Record volume of gas formed at regular intervals and plot on a graph
  3. Determine the rate of a reaction at a specific time by drawing a tangent to the curve and determining the gradient
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14
Q

What are the advantages/disadvantages of using an upside down measuring cylinder to determine the rate of reaction?

A
  • Easier to read than a gas syringe as it is slower moving
  • Lower Precision
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15
Q

What are the advantages/disadvantages of using a gas syringe to determine the rate of reaction?

A
  • Much more precise measurements
  • Gas syringe may get stuck
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16
Q

What are the advantages/disadvantages of monitoring the loss of mass of reactants using a balance?

A
  • Easy to set up and loss of gas is no problem
  • Gas (especially CO₂) may dissolve back into the solution
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17
Q

How would you determine the rate of reaction by monitoring the mass of gas lost?

A
  1. Set up the apparatus
  2. Record mass loss at regular intervals and plot on a graph
  3. Determine the rate of a reaction at a specific time by drawing a tangent to the curve and determining the gradient
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18
Q

What is a catalyst?

A

A catalyst is a substance that changes the rate of a chemical reaction without undergoing any permanent change itself.

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19
Q

Explain how a catalyst does not undergo any chemical change itself:

A

The catalyst is not used up in the chemical reaction:
* The catalyst may react with a reactant to form an intermediate or may provide a surface on which the reaction can take place.

At the end of the reaction the catalyst is regenerated

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20
Q

How does a catalyst increase the rate of reaction?

A

It provides an alternative reaction pathway of lower activation energy. Therefore more reactants have sufficient energy to react, resulting in more effective reactions and a greater rate of reaction

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21
Q

What does an enthalpy profile diagram with/without a catalyst for an exothermic reaction look like?

A
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22
Q

What does an enthalpy profile diagram with/without a catalyst for an endothermic reaction look like?

A
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23
Q

What is a homogeneous catalyst and how does it work?

A

A homogeneous catalyst has the same physical state as the reactants. The catalyst reacts with the reactants to form an intermediate. The intermediate then breaks down to give the product and regenerates the catalyst

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24
Q

What are 2 examples of reactions with homogeneous catalysts?

A
  • Making esters with a sulfuric acid catalyst (all liquids)
  • Ozone depletion with Chlorine radicals as a catalyst (all gases)
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25
Q

What is the word equation for making esters with a sulfuric acid catalyst?

A

Alcohol(l) + Carboxylic acid(l) + sulfuric acid(l) ⇌ ester(l) + water(l)

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26
Q

What is the chemical equation for Ozone depletion with Chlorine radicals as a catalyst?

A

2O₃(g) + Cl^(g) ⇌ 3O₂(g)

^ = bullet point

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27
Q

What are heterogeneous catalysts and how do they work?

A

A heterogeneous catalyst has a different physical state from the reactants. Reactant molecules are adsorbed onto the surface of the catalyst, where the reaction takes place. After the reaction, the product molecules leave the surface of the catalyst by desorption

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28
Q

What physical state are heterogeneous catalysts usually?

A

Usually solid catalysts in contact with gaseous reactants or reactants in solution

29
Q

What is adsorption?

A

Adsorption is the process that occurs when a gas, liquid, or solute is held to the surface of a solid

30
Q

What is desorption?

A

The release of an adsorbed substance from a surface

31
Q

What are 4 processes that use heterogeneous catalysts?

A
  • Haber process
  • Reforming
  • Hydrogenation of alkenes
  • The Contact process
32
Q

What is the contact process?

A

the process for making sulfur trioxide for sulfuric acid

33
Q

What catalyst does the haber process use?

A

Fe(s)

34
Q

What catalyst does reforming use?

A

Pt(s) or Rh(s)

35
Q

What catalyst does Hydrogenation of alkenes use?

A

Ni(s)

36
Q

What catalyst does the contact process use?

A

V₂O₅(s)

37
Q

What is the chemical reaction of the contact process?

A

2SO₂(g) + O₂(g) ⇌ 2SO₃(g)

38
Q

What is the economic and sustainability importance of catalysts?

A

As catalysts lower the activation energy, then a lower temperature is required for the process. If a chemical reaction requires less energy, less electricity or fossil fuels are required to provide this energy.
* This cuts costs and increases profit. The economic benefits of using catalysts far outweighs any costs involved with developing a catalytic process
* It also produces fewer pollutants/carbon emissions, increasing the sustainability of the process

39
Q

What is autocatalysis?

A

A chemical reaction is said to have undergone autocatalysis if a reaction product acts as a catalyst for that reaction

40
Q

What is the boltzmann distribution?

A

A distribution showing the spread of molecular energies in a system. The graph is plotted as “number of molecules with a given energy” against “energy”. It also contains a line, Eₐ, to mark the activation energy.

41
Q

What are 3 features of the Boltzmann distribution?

A
  • No molecules have zero energy - the curve starts at the origin
  • The area under the curve is equal to the total number of molecules
  • There is no maximum energy for a molecule - the curve does not meet the x-axis at high energy. The curve would need to reach infinite energy to meet the x-axis
42
Q

How does temperature affect the boltzmann distribution (and sketch the new curve)?

A

As temperature increases, the average energy of the molecules also increases.
* Therefore, more molecules will have higher energy, causing the graph to be stretched across a greater range of energy values, therefore more will have sufficient activation energy.
* The peak of the graph is lower on the y-axis and further along the x-axis (the peak is at a higher energy)
* The area under the curve remains the same as the number of moelcules is the same

43
Q

How does temperature affect the rate of reaction?

A

At higher temperature:
* More molecules have an energy greater than or equal to the activation energy
* Therefore a greater proportion of collisions will lead to a reaction, therefore increasing the rate of reaction
* Collisions will also be more frequent as the molecules are moving faster, but the increased energy of the collisions is much more important than the increased frequency of collisions

44
Q

How does a catalyst affect the boltzmann distribution (and sketch the new curve)?

A

A catalyst provides an alternative reaction route with lower activation energy. Therefore the Eₐ line will shift to the left as a greater proportion of molecules have sufficient energy. The curve itself is completely unchanged

45
Q

What is a reversible reaction?

A

A reaction that can take place in the both the forward and reverse directions

46
Q

What is true in an equilibrium system?

A

In an equilibrium system:
* The rate of forward reaction is equal to the rate of the reverse reaction
* The concentration of reactants and products does not change

47
Q

What does “Dynamic” equilibrium mean?

A

Equilibrium is dynamic as when the rate of forward reaction increases, the rate of reverse reaction will increase to keep the concentration of reactants and products constant

48
Q

What are the conditions for an equilibrium system?

A

A closed system

49
Q

What is the position of equilibrium?

A

The relative quantities of reactants and products, indicating the extent of a reversible reaction at equilibrium

50
Q

What is “Le Chatelier’s principle”?

A

When a system in equilibrium is subjected to an external change, the system readjusts itself to minimise the effect of that change

51
Q

What is the effect of concentration changes on equilibrium?

A
  • If the concentration of reactants increases, the position of equilibrium will shift to the right in order to form more products
  • If the concentration of products increases, the position of equilibrium will shift to the left in order to form more reactants
52
Q

How can you investigate changes to the position of equilibrium with concentration?

A

Using aqueous chromate ions (CrO₄²⁻) and dichromate ions (Cr₂O₇²⁻) as they are sensitive to changes in acid concentration. Solutions of chromate ions are yellow whereas they are orange for solutions of dichromate. You can change the concentration using sulfuric acid and sodium hydroxide:
1. When you add sulfuric acid, you are increasing the concentration of H+ ions. Therefore there is an increase in the concentration of reactants
2. Therefore the position of equilibrium shifts to the right in order to produce more products
3. The solution turns orange as a result
4. When you add Sodium Hydroxide, the added OH- ions react with the H+ ions, decreasing the concentration of reactants and increasing the concentration of products
5. As a result the position of equilibrium shifts to the left in order to produce more reactants
6. The solution turns yellow as a result

53
Q

What colour is a solution of chromate ions (CrO₄²⁻)?

A

Yellow

54
Q

What colour is a solution of dichromate ions (Cr₂O₇²⁻)?

A

Orange

55
Q

How can you investigate changes to the position of equilibrium with temperature?

A

Dissolve Cobalt Chloride in water:
1. Dissolve cobalt chloride in water in a boiling tube. Add a small quantity of hydrochloric acid
2. Place boiling tube into an ice bath, the solution should turn pink. This is because when you decrease the temperature, the reaction moves in the exothermic direction to minimise the decrease in temperature.
3. Transfer boiling tube to a boiling water bath, the solution should turn blue. This is because when you increase the temperature, the reaction moves in the endothermic direction to minimise the increase in temperature.

56
Q

How does temperature affect the position of equilibrium?

A
  • If the temperature is increased, the point of equilibrium will move in the endothermic direction in order to minimise the increase in temperature
  • If the temperature is decreased, the point of equilibrium will move in the exothermic direction in order to minimise the decrease in temperature
57
Q

How does changing the pressure affect the position of equilibrium?

A
  • Increasing the pressure on an equilibrium system will cause the position of equilibrium to move towards the side with fewer gaseous molecules
  • Decreasing the pressure on an equilibrium system will cause the position of equilibrium to move towards the side with a greater number of gaseous molecules
58
Q

How can you investigate changes to the position of equilibrium with pressure?

A

The gases nitrogen dioxide and dinitrogen tetroxide form the equilibrium: “2NO₂(g) ⇌ N₂O₄(g)”.
* Increasing the pressure causes the mixture to become more colourless as the position of equilibrium is shifted to the right
* Decreasing the pressure causes the mixture to become more brown as the position of equilibrium is shifted to the left

59
Q

When does changing the pressure not affect the position of equilibrium?

A

When there are an equal number of gaseous molecules on either side of the equation

60
Q

What is the effect of a catalyst on an equilibrium system?

A
  • A catalyst does not affect the position of equilibrium as it speeds up the rate of forward and reverse reactions equally
  • However, as a catalyst increases the rate of reaction, it increases the rate at which an equilibrium is established
61
Q

What is an equilibrium constant, Kc?

A

A measure of the position of equilibrium; the magnitude of an equilibrium constant indicates whether there are more reactants or more products in the system

62
Q

What is the general equation for a reversible reaction?

A

aA + bB ⇌ cC + dD

63
Q

What is the equilibrium law?

A
64
Q

What do square brackets mean?

A

[ ] = concentration of

65
Q

What does the equilibrium constant tell you?

A
  • When Kc = 1, the position of equilibrium is half way between the prodcts and reactants
  • When Kc > 1, the position of equilibrium is towards the products
  • When Kc < 1, the position of equilibrium is towards the reactants
66
Q

What do catalysts effect in an energy profile diagram?

A
  • The activation energy (Ea) is lower
  • However, the ΔH does not change
67
Q

What is activation energy?

A

The minimum energy required to start a chemical reaction by breaking reactant bonds

68
Q

How does the yield of products change with the position of equilibrium?

A

The yield of products increases when the position of equilibrium is further to the right

69
Q

What is a homogeneous equilibrium?

A

When all the products and reactants are in the same state

A Level Chemistry (31 decks)

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