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Chemistry > Reactivity 2.2 > Flashcards

Reactivity 2.2 Flashcards

1
Q

Molecularity

A

The number of particles taking part in any specified step

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2
Q

Unimolecular

A

An elementary step that involves a single reactant particle

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3
Q

Bimolecular

A

An elementary step with two reactant particles

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4
Q

What is the activation energy in a single step reaction?

A

The minimum energy required to reach the transition state before products are formed.

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5
Q

Rate determining step

A

The slowest step of a reaction. It has the highest activation energy

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6
Q

Rate of reaction

A

Increase in conc of one of the products per unit time or decrease in conc of one of the products per unit time

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7
Q

Rate of rxn common units

A

mol dm^-3 s^-1

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8
Q

What can be used to determine the rate of a chemical reaction?

A

Any technique that enables the change in conc of one of the products or reactants to be measured over time

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9
Q

Gradient of a conc/time graph=?

A

Rate of rxn

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10
Q

Collision theory

A

Particles must collide..
- at the correct orientation
- with sufficient energy to break existing bonds in the reactant species (min for this is known as activation energy)

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11
Q

Maxwell-Boltzman energy distribution curve

A
  • Expresses that different particles in a gas at (a specific temp) have a range of kinetic energies
  • area under curve represents the total number of particles in the sample
  • can be used to explain the effect of changing temps and the use of a catalyst on the probability of successful collisions occurring
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12
Q

Effect of increasing reactant concentration (or pressure in rxns with gaseous reactants) on rate of rxn

A

(Initial) Rate of rxn will inc as conc is inc. This is because there are more reactant particles, therefore more collisions, therefore more successful collisions per sec.

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13
Q

Effect of increasing temp on rate of rxn

A

Rate of rxn will inc as the temp inc. This is because the particles are moving more quickly and are therefore colliding more often with greater energy.

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14
Q

Effect of increasing surface area on rate of rxn

A

Rate of rxn will inc as the surface area inc. This is because only the surface particles will come into contact with the other reactant/s. Therefore the greater the surface area the greater the amount of available particles.

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15
Q

Effect of catalysts on rate of rxn

A

The rate of rxn will be increased in the presence of a suitable catalyst. They do this by bringing the reactive parts of the reactants close together, providing an alternate pathway with a lower activation energy. Meaning more of the particles can reach the Ea threshold.

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16
Q

Catalyst

A

A substance that increases the rate of the reaction without being permanently changed chemically.

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17
Q

If the eq for the rate determining step is: A –> products , what is the molecularity and the rate eq?

A

Molecularity: Unimolecular
Rate eq: k[A]

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18
Q

If the eq for the rate determining step is: 2A –> products , what is the molecularity and the rate eq?

A

Molecularity: Bimolecular
Rate eq: k[A]^2

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19
Q

If the eq for the rate determining step is: A + B –> products , what is the molecularity and the rate eq?

A

Molecularity: Bimolecular
Rate eq: k[A] [B]

20
Q

What is the activation energy in a single step rxn?

A

The min energy required to reach the transition state before products are formed

21
Q

What is formed in a two step rxn?

A

An intermediate

22
Q

What is the activation energy in a two step rxn?

A

Overall Ea is the difference in energy between the reactant state and the highest energy transition state. Each step in a two step rxn has its own Ea, the slow step will have the highest Ea.

23
Q

Order of rxn with respect to a particular reactant

A

The power to which it’s conc term in the rate eq is raised

24
Q

When rate=k[A]^x+[B]^y, what is the overall rxn order?

A

x+y

25
Q

Rate constant (k)

A

A fixed value, for a specific rxn, at a specified temp.

26
Q

Is the rate constant determined experimentally or by the stoichiometric eq?

A

Experimentally

27
Q

What order is radioactive decay?

A

First order

28
Q

Units of K for a zero order rxn

A

mol dm^-3 s^-1

29
Q

Units of K for a first order rxn

A

s^-1

30
Q

Units of K for a second order rxn

A

mol^-1 dm^3 s^-1

31
Q

Units of K for a third order rxn

A

mol^-2 dm^6 s^-1

32
Q

What order rxn are these units for: mol dm^-3 s^-1

A

Zero

33
Q

What order rxn are these units for: s^-1

A

First

34
Q

What order rxn are these units for: mol^-1 dm^3 s^-1

A

Second

35
Q

What order rxn are these units for: mol^-2 dm^6 s^-1

A

Third

36
Q

Though proposed mechanisms cannot be proven they must be consistent with…

A

the rate expression

37
Q

The rate constant is dependent on..

A

temp

38
Q

Why is the rate constant temp dependent?

A

As temp inc, reactants have more energy meaning more particles will possess the necessary Ea, the freq of collisions per unit time will also inc

39
Q

What is A for in the Arrhenius eq?

A

the freq factor (or the arrhenius constant, or the pre-exponential factor)

40
Q

The exponential factor

A

e^-Ea/RT, represents the fraction of the reactant particles that have sufficient energy to react.

41
Q

Frequency factor constant (A)

A

relates to the freq of collisions and the steric factor (frac of collisions between reactant species with the correct orientation to react). Has the units of the rate constant.

42
Q

Steric factor

A

fraction of collisions between reactant species with the correct orientation to react

43
Q

What can be found from a graph of ln k against 1/T

A

A straight line graph where the intercept (extrapolated back to y axis)= A and the grad= -Ea/R

44
Q

Formula for determining the values of Ea and A for a rxn using simultaneous eqs

A

ln (k1/k2) = Ea/R [(1/T2)-(1/T1)]

45
Q

Which is the rate determining step in a two step eq?

A

The slowest/ the one that has the largest Ea

Chemistry (11 decks)

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