This chemistry document covers several topics: 1) Reaction rates can be measured using the continuous or initial rate methods, and the rate determining step is the step that includes the reactant in the rate equation. 2) Kinetics follow first order, second order, or zero order rate laws depending on the reaction. 3) Nucleophilic substitution reactions can proceed by SN1 or SN2 mechanisms. 4) The Arrhenius equation relates reaction rate to temperature. 5) Heterogeneous catalysts increase reaction rates by providing an active surface for reactants to adsorb to.

1. +
Chemistry
Unit 4

2. + Reaction Rates
It’s the change in the amount of reactants or products per unit time
Continuous Rate Method
If it’s in the Rate
Equation then it’s the
Rate Determining Step
Initial Rate Method
1st Order:
•
•
Rate = k[X]1
Constant Half Lives
2nd Order:
• Rate = k[Y]2
• Increasing Half Lives
0 Order:
• Rate = k[Z]0
1o Halogenoalkane + Hydroxide = SN2
3o Halogenoalkane + Hydroxide = SN1

3. + Nucleophilic Substitution
SN2
SN1
Slow
Fast
Iodine + Propanone
Slow
Fast
Fast
Fast

4. + Arrhenius Equation
ln(k) =
-Ea
X
R
1
+ Constant
T
R = Gas Constant (8.314)
T = Temperature (Kelvin)
1/temp (k)
Gradient =
ln( 1/time)
x
y
X
Y

5. + Heterogeneous Catalysts
• In a different state to the reactants
• Large surface area as they’re usually powder or a mesh
• Easily separated from products & excess reactants
• Can be poisoned:
• Adsorbs too strongly to surface of catalyst and doesn’t allow other
reactants to adsorb to the catalyst
• e.g. – Nickel in Hydrogenation of Vegetable Oil
– Platinum in catalytic converters in cars
Adsorb – forms a
temporary bond when
something sticks to a
surface
How do they work?
-
Reactant adsorbed onto surface of catalysts at the active site
Interaction between reactant & catalyst
Reaction occurs from the interaction
Products are desorbed – breaks off catalyst
Homogeneous Catalyst is
when catalyst is in the same
state to reactants

6. + Entropy
Entropy change of a reaction is measure of order or disorder
The order within is a substance is how the quanta of energy are arranged
Reaction will occur if overall entropy is increasing, from order to disorder
If entropy is +ve then reaction will tend to occur
But doesn’t exist
Ordered
Disordered
More disorder = more +ve SΘ
Solid  Ordered
Liquid  Disordered
Gas  Very Disordered
More Complex/Moles  More Disordered

7. +

8. + Carbonyls
Carbonyl Group
Ethanal
Propanone

9. + Reactions of Carbonyls
dil H2SO4
Reaction with Dichromate:
-
Aldehydes can be oxidised
- Orange  Green
Ketones can’t be oxidised
LiAlH4 (in Dry Ether) to go
from Carb Acid to 1o or
Aldehyde
3RCHO + Cr2O7- + 8H+  3RCOOH + 2Cr3+ + 4H2O
AgNO3
dissolved Reaction with Tollens:
in NH3(aq) - Aldehydes +ve Silver Mirror Forms
Dissolved
in NaOH
Reaction with Benedicts:
-
Aldehydes + ve Blue (Cu2+)  Red Precipitate (Cu+)
Dissolved
in
Reaction with Brady’s:
Methanol
(2,4 DNP or 2,4 DiNitroPhenylhydrazine)
& conc
- Carbonyls +ve Orange Precipitate
H2SO4
Melting point used to identify Carbonyl compound
Presence Reaction with Iodine:
Triiodomethane
of Alkali - Methyl group adjacent to C=O +ve Pale Yellow Precipitate, Antiseptic smell

10. + HCN Reactions
Propanone + HCN
Ethanal + HCN
Nucleophilic Addition
2 methyl 2 hydroxypropanenitrile
2 hydroxypropanenitrile
In a lab HCN made by reacting KCN(s) + H2SO4

11. + Carboxylic Acids
Very soluble in H2O
Longer chain, less soluble
H-Bonding in Pure Ethanoic Acid (Dimer Shape)
Sodium
Ethanoate
Acid + Alcohol  Ester + H2O
Weak acid –
Partially Dissociate
Identifying Carboxylic Acids:
Add Sodium Carbonate – effervescence if +ve
Reaction with PCl5:
Add NH3 white
smoke = +ve
CH3COOH + PCl5  POCl3 + HCl + CH3COCl
Ethanoyl Chloride
Formed from:
- Oxidising a 1°
- Hydrolysis of Nitrile (Reflux
with dil HCl and distil off)

12. + Esters
Acid Hydrolysis:
- Reflux with dil HCl or H2SO4
Dicarboxylic Acid + Diol Alcohol  Polyester
Base Hydrolysis:
- Reflux with dil Alkali (e.g. NaOH)
Transesterification

13. + Soap & Triglycerides
Fats solid at RTP
Triglycerides have lower melting point due to less regular shape
Hydrogenation:
- Nickel catalyst @ 150°C
- Unsaturated  Saturated FA
- Solidifies fats

14. + Acyl Chlorides
Ethanoyl Chloride
Reaction with H2O:
CH3COCl(l) + H2O(l)  CH3COOH(l) + HCl(g)
Reaction with Alcohol:
-amide
CH3COCl(l) + CH3CH2OH(l)  CH3COOCH2CH3(l) + HCl(g)
Ethyl Ethanoate
Reaction with Ammonia:
CH3COCl(l) + NH3(aq)  CH3CONH2(aq) + HCl(g)
Ethanamide
N-“substituted”-Amide
Reaction with Ethylamine:
CH3COCl(l) + C2H5NH2(aq)  CH3CONHCH3CH2(aq) + HCl(g)
N-Ethyl-Ethanamide

15. + Isomerism/Optical Isomers
Only occurs when chiral carbon present:
- Carbon with 4 different groups attached
Enantiomers/Optical Isomers
Mirror
Racemic Mixture:
Contains equal amounts of each enantiomer

16. + Equilibria (Kc)
Dynamic Equilibria:
- The forwards reaction and back reaction are at the same rate so
there’s no overall change in yield of products or reactants in a closed system

17. + Kp

18. + Effects on Equilibria
Adding a catalyst:
• Equilibrium constants not affected
• Position of equilibria not affected
• Speeds up forward & backward reaction at same rate
Change in concentration:
• Equilibrium constants not affected
• Adding reactant shifts equilibria right
• Adding product shifts equilibria left
Change in pressure:
• Equilibria shifts to side with fewest molecules
• Equilibrium constants not affected
Increase in temperature:
• Endothermic = +ve shifts right, more product produced
• Exothermic = -ve
shifts left, more reactant produced
• Kc & Kp:
• Increases if endothermic
• Decreases if exothermic

19. + Uses in Industry
They alter conditions to produce maximum yield
Requiring least amount of energy
Often looking for new more environmentally friendly catalysts
e.g.
Ethene + H2O  Ethanol
Sped up by using catalyst (Silica soaked in H3PO4)
Remove product as it’s being formed

20. + Acid Theories
H+ = H3O+
Arrhenius:
Lewis:
- Acids are H+ producers
- Bases are OH- producers in H2O
- Only used in aqueous solutions
- Acid is an electron pair acceptor
- Bases is an electron pair donor
Bronsted-Lowry:
- Acids are proton donors
- Bases are proton acceptors
HA + H2O
H3O+ + A-
Conjugate Pairs
Amphoteric Substances:
• It acts a base or an acid
A base has a lone pair of
electrons which can form a
dative covalent bond with a H+
H2O & HA are Acids & Bases as they give & accept H+
HA is the acid & A- is it’s conjugate base
H2O is the base & H3O+ is it’s conjugate acid
H3O+

Base
H2O

Acid
OH-

21. + pH Strong Acids or Strong Bases
pH = - log 10 [ H+ ]
[ H+ ] = 10-pH
Kw @298k = 1x10-14

22. + pH Strong Acid & Strong Base
Excess [ OH- ]
Excess [ H+ ]

23. + pH
Weak Acids
pKa = -log10( Ka )
Larger pKa = Weaker Acid