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CHEM 203 > Chemical Kinetics Part I > Flashcards

Chemical Kinetics Part I Flashcards

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1
Q

What is kinetic energy?

A

This is the energy of motion - the energy that is a product of the object’s speed and mass.

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2
Q

Why is the area under the curve the same for 2 different scenarios?

A

The area under the curve is the same because the amount of particles or molecules is the same in both cases.

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3
Q

When would the area under the curve differ between the 2 situations?

A

The area under the curve would differ when there is a different amount of particles or molecules.

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4
Q

What is the collision theory?

A

It can be used to explain the changes that occur at the molecular level that the molecules must collide.

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5
Q

What is the transition state?

A

This is the highest energy state.

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6
Q

What is enthalpy?

A

This is the energy of the reaction as it is the difference in energy between the reactants and products it is also the total kinetic and potential energy that is in the chemical system.

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7
Q

What is the activation energy?

A

This is the energy needed to start the reaction this is the energy difference between the reactants and the transition state.

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8
Q

Which speed corresponds with each activation energy?

A

A smaller activation energy means that the reaction is fast.

A larger activation energy means that the reaction is slow.

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9
Q

What is the difference between a transition state and an activated complex?

A

The transition state is the highest energy level of the reaction and the activated complex is a short-lived complex where the configuration is somewhere between the reactants and the products at the transition state.

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10
Q

What impacts the collision frequency?

A
  1. ) Temperature
  2. ) Number of particles
  3. ) Catalyst
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11
Q

What is the Rate Determining Step (RDS)?

A

The rate of the mechanism will be no faster than the rate of its slowest rate.

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12
Q

What is the reaction mechanism?

A
  1. ) The steps must sum to the overall reaction of interest.
  2. ) Each step in the reaction is called the elementary step.
  3. ) The rate of the mechanism will be no faster than the rate of its slowest rate this is the RDS.
  4. ) Mechanisms are consistent with experimental observations.
  5. ) The overall reaction is the sum of all the elementary steps.
  6. ) An intermediate is produced in one elementary step and then consumed in another elementary step.
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13
Q

What is the energy for endothermic reactions?

A

The reactants are lower than the energy of the products.

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14
Q

What is the energy for exothermic reactions?

A

The reactants are higher than the energy of the products.

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15
Q

Why is one activation energy greater than the other?

A

One activation energy is greater than the other because it requires more energy in order to break the bonds while the other is not breaking bonds.

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16
Q

How does the speed of the reaction correspond with the activation energy?

A

A higher activation energy results in a slower reaction because fewer particles are able to attain the energy required to reach the activation energy. While a smaller activation energy results in a faster reaction because it is easily attainable.

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17
Q

What is a catalyst?

A

It will only impact the rate of the reaction not the yield. It is not a reactant or a product and it will affect a reaction mechanism. Also it will be consumed by one step AND reformed by a subsequent step so it will be the intermediate.

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18
Q

How does the catalyst change the rate of the reaction?

A
  1. ) Lowering the activation energy

2. ) Changing the number of steps of the reactions which will also have less activation energy

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19
Q

What is a homogeneous catalyst?

A

These catalysts are the same phase as the reaction and distributed throughout the reaction mixture. These are usually liquids or gases and are found in nature.

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20
Q

What is a heterogeneous catalyst?

A

These catalysts are usually solids that facilitate a reaction by absorbing reactants onto their surface.

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21
Q

What is a rate?

A

The change in concentration over the change in time.

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22
Q

What is the appearance rate or rate of production?

A

How fast the product appears over time.

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23
Q

What is the disappearance rate or rate of consumption?

A

How fast a reactant is being consumed over time.

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24
Q

What is the rate of the reaction?

A

How fast the reaction itself progresses over time per 1 mol of the reaction which is simply following the stoichiometric coefficients of the reaction exactly.

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25
Q

When is there 1 significant figure?

A

When there is a value such as 20 with no decimal place after the 0 the only significant digit is the 2 in 20 thus there is only 1 significant digit.

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26
Q

What is the general rate of reaction or the general rate expression?

A

Rate of the Reaction =
(1 / stoichiometric coefficient) x
(Change in Concentration / Change in Time)

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27
Q

What is a diluted solution?

A

A given substance that has a relatively small amount of solute per unit volume of the solution.

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28
Q

What happens when the reactant concentration increases?

A

The product side or right side is favored.

29
Q

What happens when the reactant concentration decreases?

A

The reactant side or left side is favored.

30
Q

What happens when the product concentration increases?

A

The reactant side or left side is favored.

31
Q

What happens when the product concentration decreases?

A

The product side or right side is favored.

32
Q

What happens when the temperature increases in an endothermic reaction?

A

The product side or right side is favored.

33
Q

What happens when the temperature decreases in an endothermic reaction?

A

The reactant side or left side is favored.

34
Q

What happens when the temperature increases in an exothermic reaction?

A

The reactant side or left side is favored.

35
Q

What happens when the temperature decreases in an exothermic reaction?

A

The product side or right side is favored.

36
Q

What happens to the kinetic energy as the temperature increases?

A

The average kinetic energy increases since the particles move faster.

37
Q

What happens to the kinetic energy as the temperature decreases?

A

The average kinetic energy decreases since the particles move slower.

38
Q

What is the enthalpy of an exothermic reaction?

A

Negative

39
Q

What is the enthalpy of an endothermic reaction?

A

Positive

40
Q

What is an effective collision?

A

A collision between reactants that result in the formation of products and that satisfy the following:

  1. ) Correct orientation/Collision geometry
  2. ) Sufficient collision energy
41
Q

What impacts the reaction rate?

A
  1. ) Decrease volume
  2. ) Increase concentration
  3. ) Raise the temperature
  4. ) Increase surface area
  5. ) Add a catalyst
42
Q

Is there a relationship between enthalpy and activation energy?

A

There is none.

43
Q

What is the average rate of reaction?

A

The change in concentration over the change in time given the time interval.

44
Q

What is the instantaneous rate of reaction?

A

The rate at a specific point in time which is found by taking the slope tangent when t = x.

45
Q

What is the initial rate of reaction?

A

The rate when t = 0 so just before the reaction takes place and this is done by taking the slope of a line that is tangent to t = 0.

46
Q

What is the Rate Law?

A

Rate = k[A]^m[B]^n

47
Q

What is the (k) rate constant?

A

This is the proportionality that relates the concentration of a specific reactant in a specific mechanism to the rate of that reaction.

48
Q

What is the order of the reaction?

A

This is the amount that the concentration impacts the rate of the reaction.

49
Q

How do you find the overall order?

A

Adding the individual orders of the reactants together.

50
Q

What if the individual order is 0?

A

Then that reactant does not have an impact on the rate of the reaction.

51
Q

What can you use to determine how much a rate has increased by?

A

The stoichiometric coefficients of the reaction can be used to determine how much greater a rate of a reactant in the reaction is at an instant in time.

52
Q

Why are we only looking at the rate and order for the reactants?

A

Since the reactants determine the products we look at the reactants only.

53
Q

What are the two ways to determine the Rate Law?

A
  1. ) Method of initial rates which is when there are a set of experiments where 1 reactant concentration is constant and the other reactant concentration is manipulated in order to determine the change in the rate of the reaction. For example, you have a set and there are 2 reactants by using the one that is changing you are finding the order of that reactant.
  2. ) Plot curves is when a single reactant in a single experiment is used in order to determine the progression of the reaction over a period of time.
54
Q

What are the steps to find the initial rates?

A
  1. ) Write the generic Rate Law.
  2. ) Find pairs in the experiment.
  3. ) Compare the concentration change to the change in rate.
  4. ) Calculate k and determine the units.
  5. ) Write down the full Rate Law with all of the components.
55
Q

What is the differential rate law?

A

Measures rate as it varies with reactant concentration.

56
Q

What is the integrated rate law?

A
  • Measures the change in concentration of one species with time and relates the change back to the rate.
  • Easier and more convenient determine experimentally.
  • Allows the determination of the concentration at a specific time during the reaction.
  • The goal is to make the plot linear.
  • Works best for 0, 1, 2 order reactions.
57
Q

What leads to a linear plot for 0, 1, or 2 order?

A 
0 = Concentration VS Time
1 = ln[Concentration] VS Time 
2 = 1/[Concentration] VS Time
58
Q

What are the 2 ways to determine order?

A
  1. ) By looking at the units

2. ) By looking at the value above the concentration in the general rate law

59
Q

What are the units for 0, 1, 2, 3 orders?

A 
0 = M/s
1 = S^-1
2 = M^-1*S^-1
3 = M^-2*S^-1
60
Q

How do you know that order matters?

A
  • For all 3 scenarios the initial concentrations are the same at 1.00M.
  • The half-life is the same for the half-life of the reaction is the time required for the concentration to decrease by 50% of the initial concentration.
61
Q

How does the order impact the rate graphically?

A

If the order is higher than another but the concentration is less then the rate will be lower and the slope of the curve will be smaller than a lower order of the same small concentration.

62
Q

Why does the ln law change from subtraction to division?

A

ln[A]o - ln[A]t = ln([A]o/[A]t)

63
Q

What does k depend on?

A

k is specific to the mechanism’s temperature, and the activation energy (the correct molecular orientation during collisions).

64
Q

How does collision frequency depend on concentration?

A

The higher the concentration the higher the collision frequency.

65
Q

How does collision frequency impact the rate of the reaction?

A

The higher the collision frequency the faster the rate of the reaction.

66
Q

What are the components of the Arrhenius equation?

A 
A = pre-exponential factor that is calculated experimentally and it represents the collision frequency with the probability that the molecules will be in the correct orientation.
e = A number on the calculator
Ea/RT = This is the exponent with the activation energy divided by the temperature and the constant
e^(Ea/RT) = The energy term
67
Q

How is the number of molecules related to Ea?

A

The lower the Ea the higher the percentage of molecules that can react.

68
Q

How is the number of molecules related to Ea and temperature?

A

The higher the temperature the higher the number of collisions thus the higher the percentage of molecules that can make it the activation energy and react.

CHEM 203 (7 decks)

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