Chapter 8. Reaction Kinetics

Question 1

What is the collision theory?

Answer 1

For a reaction to take place between two particles they must coolide with enough energy to break bonds and they must occur in the right orientation

Question 2

What are the factors that affect rate of reaction?

Answer 2

Temperature
-An increase in temperature increases the kinetc energy of particles leading to a higher frequency of collisions
concentration of a solution
-more particles in a given volume, collisions more likely to take place(higher collision frequency) but reactants get used up so rate of reaction falls as the reaction carries on
Pressure of a gas reaction
-same as concentration of a solution but with gases
Surface area of solid reactants
-The greater the total surfae area of a solid, the more its particles are available for collisions. So rate of reaction increases as there are more sites for reaction.
Catalyst
-A catalyst is a substance that can change the rate of a chemical reaction without being chemically changed itself

Question 3

Define rate of reaction

Answer 3

The change in concentration of any of the reactants or products per unit time

Question 4

Sodium thiosulfate

Answer 4

Na₂S₂0₃

Question 5

Sate the Beer-Lambert law

Answer 5

The absorbance of light by a coloured species is directly proportional to its concentration

Question 6

Note

Answer 6

When sketching a Maxwell-Boltzmann curve, make sure there is a sharp rise to the peak starting from the origin and a gradual decrease but the curve doesn’t meet the horizontal axis at the end.
Vertical axis - Fraction of particles with energy E
horizontal axis - Energy E

Question 7

Note

Answer 7

Effective collisions are the ones that have enough energy to react

Question 8

Define Activation Energy

Answer 8

The minimum energy required for a collision to be effective and start the reaction (breaking bonds), E_A.
The enrgy required to reach the transition state.

Question 9

Note

Answer 9

Maxwell-Boltzmann graph
-Area under the graph is the total number of particles
-Most probable energy at the peak is different from average energy closer to the right
-Only particles after the E_A ark can react.
-At higher temperatures the peak moves lower and more to the right so the number of particles with energy greater than E_A increase therefore increasing the number of effective collisions(those with energy greater than the activation energy)
A catalyst moves the E_A mark to the left and a greater area of particles with energy greater than E_A is produced

Question 10

What is the mecahanism of a recation?

Answer 10

The series of steps by which the reactants are converted into products.

Question 11

How do catalysts work?

Answer 11

They provide a different pathway(mecahanism) with a lower E_A for a reaction

Question 12

What are the two types of catalysts?

Answer 12

Heterogenous
-Present in a different phase(state of matter) from the reactants
Homogenous
-Catalyst is in the same phase as the reactants

Question 13

Catalyst examples

Answer 13

Reaction – Catalyst – Use
-Haber process – iron – making fertilisers
-Ostwald process for nitric acid (4NH₃ + SO₂ –> 4NO + 6H₂O) – platinum and rhodium – making fertilisers and explosives
-Hardening of fats with hydrogen (H₂C=CH₂ + H₂ –> CH₃CH₃) – nickel – making margarine
-Cracking of hydrocarbon chains from crude oil – aluminium oxide and silicon dioxide zeolite – making petrol
-Catalytic converter reactions in car exhausts – platinum and rhodium – removing polluting gases
-H₂C=CH₂ + H₂O –> CH₃CH₂OH (hydration of ethene to produce ethanol) – H⁺ absorbed on solid silica phosphoric acid(H₃PO₄) – making ethanol- a fuel additive, solvent, and chemical feedstock
-CH₃CO₂H_(l) +CH₃OH_(l) –> CH₃CO₂CH_3(aq) + H₂O_(l) (esterification) – H⁺ – making solvents

Question 14

Why are rates of reaction studied?

Answer 14

(i) to discover the best conditions to make the reaction go as quickly as possible.
(ii) to gather information about the reaction mechanism, i.e. how the reaction actually takes place.