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Chemistry🧪 > P1: Kinetics > Flashcards

P1: Kinetics Flashcards

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1
Q

Explain the 3 key points of ‘collision theory’

A
  1. For a reaction to take place between two particles, they must collide with enough energy to break bonds, and be in the correct orientation
  2. To get a lot of collisions, you must have a lot of particles in a small volume, and must be moving fast to break the bonds.
  3. Most collisions between molecules or other particles do not lead to a reaction.
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2
Q

What are the 5 factors affecting rate of reaction and explain them?

A
  • INCREASING TEMPERATURE: increases both energy and number of collisions, due to a speed increase.
  • INCREASE IN CONC OF SOLUTION: more particles are present, so collisions are more likely, reaction is faster. ( same for an ^ pressure in gas).
  • INCREASE SURFACE AREA: more particles are available to collide e.g cube vs granulated sugar
  • CATALYST: lowers the activation energy without being used up itself, speeds it up, increases proportion of successful collisions.

These increase the frequency of collisions

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3
Q

Define activation energy (Ea)

A

The minimum energy required for a reaction to occur.

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4
Q

What does the ‘Maxwell Boltzmann Distribution’ tell us?

A

The distribution of energy amongst the particles

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5
Q

What are some key points to note about the ‘Maxwell Boltzmann Distribution’?

A
  • No particles have zero energy
  • Most particles have intermediate energy (around the peak of the curve)
  • A few have very high energies, there is no upper limit
  • Average energy is not the same as the most probable energy.
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6
Q

How would you work out the total number of particles using the ‘Maxwell Boltzmann Distribution’?

A

Work out the area under the graph

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7
Q

What happens to the ‘Maxwell Boltzmann Distribution’ if we increase the temperature?

A

-The curve will get lower as there are more particles with greater energy
-Also a higher number of particles with greater energy than the activation energy.
-Will skew slightly more to the right of the original curve.
-area under the curve is the same.

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8
Q

Define what a Catalyst is

A

They provide a quicker alternate pathway or route for the reaction, one with a lower activation energy, and doesn’t get used up or changed itself.

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9
Q

What catalyst is used in The Haber Process and what is the reaction?

A

Iron

N2 (g). +. 3H2 (g). &raquo_space; 2NH3 (g)

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10
Q

What catalyst is used to harden fats with hydrogen and what is the reaction?

A

Nickel

H2C=CH2 + H2&raquo_space;> CH3CH3

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11
Q

What are the catalysts in a catalytic converter in car exhausts?

A

Platinum and Rhodium

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12
Q

What catalysts are used to crack hydrocarbon chains from crude oil?

A

Zeolite, aluminium oxide, and silicon dioxide.

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13
Q

What does a catalytic converter do?

A

Reduces the number of polluting gases coming out of petrol-engine car exhausts.

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14
Q

What is the structure of a catalytic converter?

A

-A honeycomb ceramic material, coated with platinum and rhodium metals.
-Honeycomb shape provides a large surface area.

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15
Q

What is the word equation for a catalytic converter?

A

Carbon monoxide + nitrogen oxides&raquo_space;> nitrogen + carbon dioxide

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16
Q

What is Adsorption?

A

1st reaction that takes place on the surface of the catalyst.

-The gases first form weak bonds with the metal atoms of the catalyst: this holds the gases loosely, to react together.

17
Q

What is Desorption?

A

2nd reaction to take place on the surface of the catalyst.

-Products break away from metal atoms, freeing up room on the catalyst surface for more gases to take their place and react.

18
Q

Define rate of reaction

A

Measurement of change in concentration or amount of products or reactants in unit time.

19
Q

What is a transition state?

A

The top of the curve in and energy level diagram, bonds are being broken and made.

20
Q

Discuss an exothermic reaction with regards to activation energy.

A

A large activation energy means a slower reaction.

Smaller activation energy means faster reaction as it requires less energy to get going.

21
Q

Talk about endothermic energy

A

Products have more energy than reactants.

22
Q

Why don’t most collisions between gas-phase reactants not lead to a reaction?

A

The molecules do not have enough energy (sufficient).

23
Q

Why does a small increase in temp lead to a large increase in rate of reaction between colliding particles?

A

MANY more particles will have energy greater than the activation energy, so more successful collisions.

24
Q

Explain how a catalyst works

A

Creates an alternate route for reaction, lowering the activation energy= faster rate of reaction.

25
Q

How do you work out rate?

A

Rate= 1/ time

26
Q

What is a Heterogeneous catalyst?

A

Where the catalyst is in a different state/phase to the reactants.

e.g reactant: aq
catalyst: solid

27
Q

What is a Homogeneous catalyst?

A

Where the catalyst is in the same state/phase as the reactants.

e.g reactant: aq
catalyst: aq

28
Q

How do catalysts speed up reactions? (Homogeneous)

A

They lower the activation energy, so more particles can react as the have sufficient energy, therefore a faster reaction. They create an intermediate.

29
Q

How do Heterogeneous catalysts work?

A

The reaction occurs on the surface of the catalyst through adsorption, binds to active site, then desorption.

30
Q

If two molecules collide but don’t have enough energy to react, what happens?

A

They will bounce off each other, and one may gain kinetic energy from the other

31
Q

Where is the highest point of energy in a reaction profile?

A

The transition state (the peak)

32
Q

What happen to the Maxwell Boltzmann Distribution if you decrease the temperature?

A

-The peak skews to the left of the original curve
-The peak is higher
-The activation energy is lower

33
Q

What are the labels on the X and Y axis of a reaction profile?

A

X= Progress of reaction
Y= Energy

34
Q

What are the X and Y axis of a Maxwell Boltzmann Distribution ?

A

X= Energy
Y= Number of particles/molecules

35
Q

Where should the most probable energy, and average energy be on a Maxwell Boltzmann Distribution?

A

Most probable: The centre of the peak
Average: Just to the right of the most probable

36
Q

What 2 factors increase the proportion of successful collisions, therefore increasing rate of reaction?

A

Kinetic energy: the faster they move the more successful collisions as they have enough energy to break bonds

Orientation: some may repel each other and will not collide

37
Q

Briefly describe the required practical for rate of reaction

A

-Place 10cm3 of 0.05 mol/dm-3 of sodium thiosulfate into a test tube and place over the cross in water
-note the starting temperature
-add 1cm3 of hydrochloric acid and start timing
-stop timer when you can no longer see the cross and record temp
-take an average of the time
-repeat with different temps
-plot on graph

Chemistry🧪 (14 decks)

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