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CHEM 1001 > Chemical Kinetics > Flashcards

Chemical Kinetics Flashcards

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1
Q

What is rate defined as?

A

A change in some quantity per unit of time

Ex. Delta X/delta t

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2
Q

What is delta equal? Is it positive or negative?

A

Change in

Final value - the initial value

It can be both

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3
Q

If the initial value is larger than the final value delta will be?

A

Negative

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4
Q

How can you write a rate of a reactant A with a coefficient of 3?

A

-1/3(delta[A]/delta t)

Minus sign, 1/coefficient and delta concentration divided by delta time

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5
Q

How can you write the rate of a product B with coefficient 1?

A

Delta[B]/delta t

Positive, 1/1, delta B over delta t

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6
Q

Is reaction rate positive or negative?

A

Always positive

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7
Q

If one reaction rate has a coefficient of -1/3 and the rate is 4.40x10^-3 then what is the rate of a reactant with rate with a coeffienct -1/2?

A

-2(4.40x10^-3)
=-8.80x10^-3

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8
Q

What is the problem with average reaction rate? What is the solution?

A

Depends on the width of the time interval, rate changes as reaction progresses

Calculate slope of tangent to get instantaneous reaction rate

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9
Q

What is a rate law? What do the variables represent?

A

Mathematical relationship between the rate of reaction and the concentrations of reactants

Ex. Rate=k[A]^n

K is the rate constant

N is the reaction order with respect to A

A is reactant

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10
Q

What is a zero order reaction mean? What happens when you double the concentration of A?

A

Rate of reaction is always the same

Has no affect on reaction rate

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11
Q

What does a first order reaction mean? What affect does doubling the concentration of A have?

A

Rate is directly proportional to the reactant concentration

Will double the rate of reaction

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12
Q

What does a second order reaction mean? What does doubling the concentration of A do?

A

Rate is directly proportional to the square of the reactant concentration

Will quadruple the rate of reaction

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13
Q

What would graphs of 0,1,2 order reaction look like for concentration vs time? What about rate vs concentration?

A

0: decreases the steepest in straight line
1: decreases exponentially
2: decreases exponentially but shallower than 1

0: straight horizontal line
1: straight increasing line
2: exponentially increasing line

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14
Q

How can you find the rate constant of a first order reaction?

A

K=rate/[A]

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15
Q

How can you find the order of reaction from chart when the concentrations weren’t doubled?

A

Rate 2/Rate 1=([A2]/[A1])^n

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16
Q

How can you find the overall reaction order?

A

Add up the different orders

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17
Q

How can you find the rate constant of a second order reaction?

A

k=rate/[A]^2

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18
Q

What is the units for rate constant for 0,1,2?

A

0:Ms^-1

1: s^-1

2: M^-1s^-1

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19
Q

What is the difference between the differential form and integrated form? What do they look like?

A

Relationship between the rate and reactant concentration, relationship between the concentration and time

Rate=k[A]^n

[A]=f(t) (function of time)

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20
Q

What is the integrated rate law of a first order reaction?

A

ln(concentration at time t)=-kt + ln(initial concentration)

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21
Q

How can you plot the first order integrated rate law in a straight line? What is the slope equal to?

A

ln[A] vs time

x vs y

-k

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22
Q

What is the integrated rate law of a second order reaction?

A

1/(concentration at time t)=kt + 1/(initial concentration)

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23
Q

How can you plot the second order integrated rate law in a straight line? What is the slope equal to?

A

1/[A] vs time

Slope is k

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24
Q

What is the integrated rate law of a zero order reaction?

A

(Concentration at time t)= -kt +(initial concentration)

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25
Q

How can you plot the zero order integrated rate law in a straight line? What is the slope equal to?

A

[A] vs time

-k

26
Q

What is half life? What is lifetime?

A

t1/2 is the time it takes for a 1/2 of a reactant to be consumed

Lifetime is the time it takes for the concentration to decrease by 1/e, a measure of avg life expectancy of chemical species in reaction

27
Q

What is half life for first order? What about lifetime? What about when the concentration is n times lower than initial?

A

Half-life=ln(2)/k

Lifetime=1/k

n-time= ln(2)/k

28
Q

What half life does NOT depend on concentration?

A

First orders

29
Q

What is half life for second order?

A

Half-life=1/k(initial concentration)

30
Q

What is half life of zero order reaction? What is the decay time equation for n?

A

Half-life=(initial concentration)/2k

N-time= (n-1)(initial concentration)/nk

31
Q

Why does the half-life value change over course of second and zero order reaction?

A

Intitial cocnentration changes

32
Q

What is Arrhenius equation?

A

Rate constant is temperature dependent

k=Ae^(-Ea/RT)

K is rate constant

A is frequency factor

Ea is activation energy

R is gas constant

T is temperature in Kelvin

33
Q

Is the frequency factor positive or negative? What about the activation energy?

A

Positive

Positive

34
Q

When the value of the rate constant decreases what happens to Ea?

A

It increases

35
Q

What is activation energy?

A

Amount of energy needed for reaction to happen

36
Q

What is activated complex?

A

Transition state, inbetween reactants and products, not stable and cannot be isolated

37
Q

What is the difference between the frequency factor and the exponential factor in Arrhenius equation?

A

A is the number of times the molecule tries to react

Exponential is the fraction of atoms that equal or have greater energy then Ea

38
Q

What is the range of values for exponential factor?

A

0-1

Fractional so just be less then one

39
Q

How can you plot Arrhenius plot? How can you relate this to equation of a line?

A

ln(k)=(-Ea/R)(1/T) +ln (A)

ln k is y

-Ea/R is m (slope)

1/T is x

ln A is b (y intercept)

40
Q

How to find the activation energy given the slope of Arrhenius plot? What about frequency factor?

A

Ea = -(R)(slope)

Set y intercept equal to ln A, do e^y-intercept and then plug into calculator

41
Q

What is the orientation factor?

A

p

Probability of molecules colliding in correct orientation

42
Q

If p=0.16 what is the percent of successful collisions?

A

16%

Percent that collide in right orientation

43
Q

For A(g) + B(g) —> AB(g) what is orientation factor?

A

1 (100%)

44
Q

What is an example of a reaction with p>1? Why?

A

Production of KBR and Br

Harpoon mechanism (electron is transferred without collision and the resulting ions move together via coulumbic force)

45
Q

If you are given two temperatures and two rate constants how can you find the activation energy?

A

Make two Arrhenius equations and divide them, A cancels out, rearrange to get the Ea/R x 1/T1 - 1/T2, solve for Ea

46
Q

What is a reaction mechanism?

A

Series of individual chemical steps by which a chemical reaction occurs

47
Q

What is each step in a reaction mechanism called? What are species that are in mechanism but not final reaction called?

A

Elementary step

Intermediates

48
Q

What is molecularity? What are the types?

A

Number of reactant particles that collide in an elementary step

Unimolecular- one reactant

Bimolecular- 2 reactants

Termolecular- 3 reactants

49
Q

If elementary step is A->products what is rate law? What about A+A -> products? A+B-> products?

A

Rate=k[A]

Rate=k[A]^2

Rate=k[A][B]

50
Q

What is the rate determining step?

A

Limits overall rate of reaction

51
Q

What is the rate of the rate determining elementary step generally proportional to?

A

Rate of overall reaction

52
Q

How do you choose which step to make rate law for elementary step?

A

Rate determining or the one with the product formation

53
Q

When do we use steady state approx?

A

When the rate law contains an intermediate

54
Q

What are the general steps for doing a steady state approx?

A

Set d[intermediate]/dt =0

List all reactions where intermediate is involved, + for where it’s produced and - for where it’s consumed ex. K1[reactant]

Move negative terms over and isolate the concentration of intermediate

Plug value back into original rate law

55
Q

What is a catalyst?

A

Substance that increases reaction rate by lowering activation energy

56
Q

What is the difference between homo and heterogenous catalysts?

A

Homo is when they are in same phase as reactants

Herero is when they are in different phase than reactants

57
Q

What is michealis menten equation? How to use?

A

k2[E]0[S] / [S] +Km

S is substrate cocnentration and E is enzyme concentration

Decide how to simplify denominator (decide if Km is greater or less than S)

58
Q

If [S] is much greater than Km what is the rate equal to? What about us much less?

A

Rate = k2[E]0

Zero order

Rate= k2[E]0[S]/Km

First order

59
Q

How can you find out how long it takes for 35% to decay?

A

1-0.35=0.65

ln(0.65)=-kt solve for t

60
Q

What formula can be used to find the amount left after decaying?

A

Nt=N0e^-kt

Nt is amount after time decaying

N0 is initial amount

K is rate constant

T is time decaying

CHEM 1001 (6 decks)

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