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A-Level Chemistry > How Fast > Flashcards

How Fast Flashcards

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1
Q

What are factors effecting rate?

A

Temp
Conc
SA
Catalyst

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2
Q

What is rate of reaction?

A

Change in conc of a reactant (or product) per unit time.

How quickly reactants are used up/ products formed

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3
Q

What is average rate?

A

Total change in conc of reactants (or products) divided by the time taken for the reaction to take place

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4
Q

What is instantaneous rate?

A

A reaction rate of change occurring at a specific time in the reaction

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5
Q

What is the rate of reaction equation?

A

Change in conc
———————— Units: moldm-3s-1
Time

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6
Q

What are the common reaction orders?

A

Zero
First
Second

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7
Q

What is zero order?

A

When the conc of a reactant has no effect on rate

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8
Q

What is first order?

A

When the rate depends on its concentrations raised to the power of one

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9
Q

What is second order?

A

When the rate depends on its conc raised to the power of two

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10
Q

What is the rate equation?

A

Rate = K[A] ^x [B]^y

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11
Q

Give examples of methods that continuously monitor conc

A 
Change in mass
Inverted measuring cylinder
Gas syringe
pH changes - using probe/ data logger
Colorimetry - measure absorbance of reaction
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12
Q

What does the graph look like for zero order?

Conc-time graph

A

Produces straight line with negative gradient

Reaction rate does not change

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13
Q

What does the graph look like for first order?

Conc-time graph

A

Downward curve with decreasing gradient over time

As gradient decreases with time, reaction slows down

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14
Q

What does the graph look like for second order?

Conc-time graph

A

Downward curve but steeper at the start, tailing off more slowly

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15
Q

How can we tell if it is a first or second order conc-time graph?

A

Use half life

Fist order will have a constant half life (take same amount of time each at each half)

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16
Q

What is a method for measuring initial rate (conc)?

A

Clock method

17
Q

What does the graph look like for zero order?

Rate-conc graph

A

Straight line - horizontal

18
Q

What does the graph look like for first order?

Rate-conc graph

A

Straight line through the origin - diagonal

19
Q

What does the graph look like for second order?

Rate-conc graph

A

Upwards curve with increasing gradient

20
Q

What does the graph for zero order show?

Rate-conc graph

A

Rate doesn’t change

21
Q

What does the graph for first order show?

Rate-conc graph

A

Rate directly proportional to conc

22
Q

Why can’t you work out K from the second order rate-conc graph?

A

Because curve doesn’t acc confirm its 2nd. just its not 0 or 1

23
Q

What must you do to work out K from 2nd order rate-conc graph?

A

Use results from graph to plot second graph
But plot rate against [A]^2
Then find K through line gradient
Should be straight line

24
Q

What is a reaction mechanism?

A

Describes one or more steps involved in a reaction in a way which makes it clear how certain bonds are broken and made

25
Q

What is the rate determining step?

A

The overall rate of reaction (the one you could measure if you did an experiment) is controlled by the rate of the slowest step. The slowest step is called the R.D.S

26
Q

What does the rate expression tell us?

A

If the species is in the rate equation it is in the R.D.S
If it is not in the rate equation it is not in the R.D.S
The power of the substance is the number of the substance in the equation

27
Q

What must the steps involved in the reaction add up to?

A

The overall chemical equation in the reaction

eg. some compounds/elements cancel out to make overall equation

28
Q

Which step is the R.D.S?

A

Always the slowest

29
Q

What is the Arrhenius equation?

A

K = Ae ^ -Ea/RT

30
Q

What is e^ -Ea/RT?

A

Represents proportion of particles that exceed Ea and have sufficient energy to take place

31
Q

What is A?

Arrhenius equation

A

Takes in account the frequency of collisions with correct orientation
Increases slightly with temp but overall constant

32
Q

What happens to the rate constant in the Arrhenius equation when you increase temp?

A

The rate constant increases and so does rate

33
Q

What happens to the rate constant in the Arrhenius equation when you use a catalyst?

A

Decreases Ea so increases rate constant and so increases rate

34
Q

What is the more effect caused by when you increase temp in Arrhenius equation?

A

Caused by more particles exceeding Ea than increased collisions

35
Q

When can’t you extrapolate the graph?

A

When the scale is broken

36
Q

What is the inverse of Arrhenius equation?

A

Ln K = -Ea/R X 1/T + Ln A

37
Q

How do you use the inverse of Arrhenius equation calculate

A 
1. Work out Ln K and 1/T
1/ first column no.
Ln(2nd column no.)
2. Plot graph - Ln K against 1/T
3. Workout gradient 
4. Calculate A from y-intercept
Extrapolate line
38
Q

How do you find Ea from the gradient?

A

-Ea/R = X
-Ea = 8.31x
Ea = -8.31

39
Q

How do you find A when you can’t extrapolate the graph?

A

Use Ln K = -Ea/R X 1/T + Ln A
Rearrange to get Ln A
Then A = E^ Ln A

A-Level Chemistry (26 decks)

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