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OCR B Chem 4: Ozone > OZ4: Rates of Reaction > Flashcards

OZ4: Rates of Reaction Flashcards

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1
Q

What is meant by the “rate of reaction”?

A

How quickly reactants are converted into products

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2
Q

Give the formula for calculating the rate of reaction.

A

Change in property/time taken

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3
Q

Give 5 ways change in property can be measured to determine rate of reaction.

A
  • Chemical analysis
  • Volume of gases
  • Mass changes
  • PH measurement
  • Calorimetery
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4
Q

Why is it important for scientists to measure rates of reactions?

A
  • A reaction occurring too quickly can be dangerous

- A reaction occurring too slowly is impractical because it ties up equipment and people, which costs money

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5
Q

Give an example in which the volume of a gas is measured to determine rate of reaction.

A
  • Reaction between calcium carbonate and HCl produces CO2

- Gas is collected in a measuring cylinder

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6
Q

Give an example in which mass change is measured to determine rate of reaction.

A
  • Reaction between calcium carbonate and HCl produces CO2

- Mass lost of calcium carbonate can be recorded against time

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7
Q

Give an example in PH is measured to determine rate of reaction.

A
  • Reaction between calcium carbonate and HCl produces CO2

- HCl concentration falls so the PH of the reaction mixture also falls

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8
Q

What does a calorimeter do?

A

Measures change in a reaction’s colour

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9
Q

Give an example where calorimetery is used to determine rate of reaction.

A
  • When zinc reacts with copper (II) sulphate, the blue coloration of copper sulphate decreases
  • Measure the rate of this colour decreasing against time
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10
Q

Explain how chemical analysis can determine the rate of reaction.

A
  • Involves taking samples of the reaction mixture at regular intervals
  • Stopping reaction in a sample (quenching) before analysis
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11
Q

Give an example in which chemical analysis is used to determine rate of reaction.

A
  • Iodine and propanone react in the presence of an acid catalyst
  • The sample is extracted and quenched by adding sodium hydrogen carbonate, neutralising the acid
  • Amount of iodine remaining is determined by titration
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12
Q

How do you plot a graph for the rate of reaction?

A
  • Time is plotted on the x axis

- Change in property is plotted on the y axis

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13
Q

Give the conditions for a successful collision.

A
  • Must collide in the right direction
  • Must collide with correct orientation
  • Must collide with the minimum amount of Kinetic energy required
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14
Q

What are liquid and gas particles always doing?

A

Always moving and colliding

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15
Q

Why is initial reaction the fastest?

A
  • As the reaction continue, the concentration of reactants decreases
  • Less frequent collisions between reactant particles
  • Decreased rate of reaction
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16
Q

What does an increased rate of reaction mean in terms of collisions?

A

Increase in collisions in a given time between reacting particles

17
Q

Define “activation energy”

A

The minimum amount of kinetic energy required by a pair of colliding particles before a reaction occurs

18
Q

What is activation energy needed for?

A

To make or break bonds

19
Q

What happens at the highest point of an enthalpy profile diagram?

A

Transition state:

  • Old bonds stretch and break
  • New bonds form
20
Q

In an exothermic enthalpy profile are the reactants higher up or lower down than the products?

A

Higher

21
Q

In an endothermic enthalpy profile are the reactants higher up or lower down than the products?

A

Lower

22
Q

What does a Maxwell-Boltzmann Distribution graph show?

A

The distribution of different kinetic energies in a gas

23
Q

What does the area under a Maxwell-Boltzmann Distribution graph represent?

A

The number of molecules

24
Q

Are there more particles on the left or the right side of a Maxwell-Boltzmann Distribution graph?

A

On the right side

25
Q

Where on a Maxwell-Boltzmann Distribution graph is the max number of particles with a specific energy?

A

In the middle on the highest peak on the graph

26
Q

Where on a Maxwell-Boltzmann Distribution graph is the average energy shown?

A

In between the middle and Ea on the graph

27
Q

What factors influence rate of reaction?

A
  • Temperature
  • Radiation intensity
  • Concentration/pressure
  • Catalyst
  • Particle size
28
Q

How does increased temperature increase rate of reaction?

A
  • Increased temperature, means particles on average have more kinetic energy and will move faster
  • A greater proportion of molecules will have the activation energy and will react
  • So there will be a higher frequency of collisions which involve energy equal to activation energy
  • So there will be more successful collisions in a given time (e.g per second)
29
Q

How does increased temperature change a Maxwell-Boltzmann Distribution graph?

A
  • The peak of the curve is lower
  • Graph is shifted to the right
  • But same total area under the graph
30
Q

Why is the peak of the curve shifted lower?

A

To balance out other areas of the graph increasing so there is a same total area under the graph

31
Q

What happens to the most probable and average energy when temperature increases?

A

They also increase

32
Q

How does the amount of particles with the greater than/same energy as activation energy?

A

More particles

33
Q

How does increased concentration/pressure increase rate of reaction?

A
  • Particles are closer together on average
  • More particles per cm^3
  • So they collide more often, leading to more successful collisions per second
34
Q

How does increased concentration/pressure change a Maxwell-Boltzmann Distribution graph?

A
  • Area under the graph is bigger because they are more molecules
  • So same shape of graph but the curve is higher up
35
Q

How does particle size increase rate of reaction?

A
  • Powder is better than a lump

- Because there is a greater surface area making collisions more likely

36
Q

How does a catalyst increase rate of reaction?(2)

A
  • Provides an alternative pathway for a reaction

- with a lower activation energy

37
Q

How does using a catalyst change a Maxwell-Boltzmann Distribution graph?

A
  • Put the Ea line further up the graph

- Because at any given temperature, a larger proportion of particles collide successfully

OCR B Chem 4: Ozone (7 decks)

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