2.3 Knetics

Question 1

What is rate in chemical reactions?

Answer 1

Change in concentration of a species over time

Question 2

What is the concentration unit?

Answer 2

mol/ L OR M

Question 3

What is the time unit?

Answer 3

seconds

Question 4

Rate units

Answer 4

M/s

Question 5

Activation energy

Answer 5

Minimum energy required to initiate a chemical reaction

Difference between reactants and the transition state (on graph)

Question 6

What is the highest point on a reaction coordinate diagram?

Answer 6

Transition state

Question 7

What shows the energy change of a reaction, on a graph

Answer 7

Difference between reactants and products

ΔH if enthalpy

Question 8

Area under maxwell boltzmann distribution = ?

Answer 8

Total number of particles

Question 9

What happens to maxwell boltzmann distribution hen temperature is INCREASED?

Answer 9

• curve shifts to right
• maximum point / mean value is lower and further to right
• smaller number of particles with low energy
• larger number of particles with energy > Ea (Ea stays same)
• More successful collisions

Question 10

What does adding catalyst do to maxwell boltzmann distribution?

Answer 10

• Lowers Ea (further to right)
• more particles with energy > Ea
• ∴ rate of reaction increases

Question 11

How do catalysts speed up reaction?

Answer 11

Form an alternative reaction pathway

Question 12

What does Km show?

Answer 12

How effectively an enzyme can bind to its substrate

Question 13

What does Vmax show?

Answer 13

How efficient the enzyme is at catalysing the reaction

Question 14

What do 0 orders depend on?

Answer 14

Depend on a saturatable enzyme or a saturatable catalyst

Question 15

Increased surface area …………… rate of reaction

Answer 15

Increases

Question 16

Why are many powdered substances (eg. Flour) highly flammable?

Answer 16

• carbohydrates with lots of C H and O
• Have a very high SA
• Burn very rapidly if Ea is reached

Question 17

Increasing pressure …………….., the rate of reaction

Answer 17

Increases

NOTE: Apart from 0 order reactions (eg. When enzyme is saturated)

Question 18

What is the general rate equation of a reaction?

Answer 18

rate = K [A]* × [B]*

• = power = order wrt agent

Question 19

Σ powers in a rate equation =

Answer 19

Overall order of reaction

Question 20

What is K in rate equation?

Answer 20

K = Ae ^(Ea/RT)

A = likelihood of collisions being in correct lineup
R = gas constant
T = Temperature in k

Question 21

What determines the rate equation?

Answer 21

Slowest step

This has the slowest rate constant (k)

Question 22

In zero order reactions, rate is equal to….?

Answer 22

Rate = K

Question 23

What are characteristics of a 0 order concentration time graph

Answer 23

• straight linear line
• gradient = -k

Question 24

In zero order reactions, the rate is independent to…..

Answer 24

The concentration of reactant

Question 25

In first order reactions, the rate is....

Answer 25

Proportional to the concentration of a single reactant raised to the first power

Question 26

What is the shape of a concentration time graph of a first order reaction?

Answer 26

Curve Doing the log of the graph will give you a straight line graph

Question 27

In first order reactions, the half lives are....

Answer 27

Constant They depend in the rate constant K

Question 28

What is half life?

Answer 28

The time taken for the concentration of a reactant to drop to half its original value

Question 29

In zero order reactions, the half lives....

Answer 29

Get shorter

Question 30

In higher order reactions, the half lives.....

Answer 30

Get longer

Question 31

What is the sum of exponents in a second order reaction?

Answer 31

2

Question 32

What shape are lines of different orders in graphs with rate against concentration?

Answer 32

0 - straight line parallel to x axis 1st - linear (rate is proportional to concentration) (gradient = k) 2rd - exponential (rate =k²)

Question 33

What is molecularity?

Answer 33

The number of individual molecules taking part in the rate determining step

Question 34

Unimolecular rate determining step =

Answer 34

Rate = k[A]

Question 35

Biomolecular rate determining steps =

Answer 35

Rate = k[A]² Rate = k[A][B]

Question 36

Trimolecular rate determining steps =

Answer 36

Rate = k[A]³ Rate = k[A]²[B] Rate = k[A][B][C]

Question 37

What can make the same starting materials form different products, in organic and enzyme chemistry?

Answer 37

Different reaction conditions Must be reversible reaction 2 possible sets of products with different energies

Question 38

What is the thermodynamic product of a reaction?

Answer 38

One that takes the system to the most stable state

Question 39

What is used to get to thermodynamic products?

Answer 39

High reaction temperatures Long reaction times

Question 40

What is the kinetic product?

Answer 40

The one that's fastest to get to Ans has the lowest Ea

Question 41

What conditions used to form kinetic products?

Answer 41

Low temperature Short reaction times

Question 42

Which species appear in rate equation?

Answer 42

Everything upto and including the rate determining step