Chem kinetics pt 1 L13 Flashcards

1
Q

Two imp things of a chem reaction

A

*How far it goes (thermodynamics)
*How fast it goes (kinetics)

TWO ARE NOT RELATED

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2
Q

What are the two parts to studying kinetics?

A

Experimental and Theoretical

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3
Q

Experimental

A

measure reaction rates i.e measure speed and study the factors that influence them i.e what speeds/slows down a reaction

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4
Q

Theoretical

A

understand rates in molecular terms i.e what makes a reaction inherently fast/slow and use the exp data to probe reaction mechanisms

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5
Q

What is a reaction mechanism?

A

intermediate steps that a reaction takes to reach completion

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6
Q

What do we ask in a rate of reaction?

A

How does concentration change over time

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7
Q

To quantify a curved rate of reaction:

A

Find the gradient of the reactant over time, this is called a rate

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8
Q

What does a -ve rate mean?

A

We cannot have a negative rate so this means that the conc. is decreasing (the -ve sign in front of a term of reactant)

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9
Q

For general reaction:

A

aA + bB –> cC + dD

rate = -1/a (dA)/dt = 1/c (dC)/dt

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10
Q

Factors that affect the rate of reaction

A

*Chem nature
*Physical states of the reactant + products
* Conc.
*temp

NOT INVOLVED IN STOIC - no net change
*Catalyst
*inhibitor

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11
Q

How does conc. of reactants affect the rate?

A

*Conc. of reaction increases then speed increases
*Conc. of reaction increases but no affect on speed eg u drink too much beer but ur body only processes a certain amount in time

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12
Q

Rate law, order and constant

A

Rate law: rate = k [A]ˆx [B]ˆy

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13
Q

What does rate law say?

A

If you change the conc.,this is how it will change the rate

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14
Q

Can i ignore stoic for rate law

A

YAS

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15
Q

How to determine rate law?

A

Through experiments as we cannot find x and y without it

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16
Q

What is x and y

A

x - order with respect to A
y = order with respect to B
x + y = total order of reaction

Usually integers from 0 - 2

17
Q

what do 1st order reactions do?

A

Behave the same

18
Q

How to get 1st order reactions?

A

*1st order in A where reaction has only one reactant
*1st order in A where reaction has 2+ reactants but all other reactants are 0

19
Q

Pseudo 1st order reaction

A

Increasing the conc. of B in a reaction so that its conc. is relatively constant i.e it is not being used up much so we can write rate exp in terms of one reactant

k’ = k[B]

Rate = k’[A]

20
Q

Purpose of a pseudo 1st order reaction

A

Easier to find the rate by working with only 1 reactant (forcing the other reactant to not change)

21
Q

Rate of order changes with conc.

A
  • 0 order - change in conc. has no affect on rate change
  • 1st order - rate doubles

*2nd order - rate increases by 4 = k[A]ˆ2
rate increases by 2 = k[A][B]

22
Q

Rate constant k

A

*Independent of conc.
*increases with temp
*Gives constant of proportionality
*units depend on overall x+ y

23
Q

units when order = 0

24
Q

units when order = 1

25
units when order = 2
L mol-1s-1
26
units when order = 3
Lˆ2 mol-2 s-1
27
Relationship between rate and time
Inverse relationship
28
How does the rate constant change
If the order changes
29
What is the isolation method?
Varying the conc. of one reactant and holding the others constant