+

ChemistryUnit 4

+ Reaction RatesIt’s the change in the amount of reactants or products per unit time

1st Order:• Rate = k[X]1

• Constant Half Lives2nd Order:• Rate = k[Y]2

• Increasing Half Lives0 Order:• Rate = k[Z]0

Continuous Rate Method

Initial Rate Method

1o Halogenoalkane + Hydroxide = SN2

3o Halogenoalkane + Hydroxide = SN1

If it’s in the Rate Equation then it’s the Rate Determining Step

+ Nucleophilic SubstitutionSN2

SN1

Iodine + Propanone

Slow Fast

Fast

Fast Fast

Slow

+ Arrhenius Equation

ln(k) = X + Constant-Ea 1 R T

R = Gas Constant (8.314)T = Temperature (Kelvin)

1/temp (k)

ln( 1/time)x

y

Gradient = XY

+ 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

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

Adsorb – forms a temporary bond when something sticks to a surface

Homogeneous Catalyst is when catalyst is in the same state to reactants

+ EntropyEntropy 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

Ordered

Disordered

But doesn’t exist

More disorder = more +ve SΘ

Solid OrderedLiquid Disordered Gas Very Disordered

More Complex/Moles More Disordered

+

+ Carbonyls

Ethanal PropanoneCarbonyl Group

+ Reactions of Carbonyls

Reaction with Dichromate:- Aldehydes can be oxidised

- Orange Green- Ketones can’t be oxidised

3RCHO + Cr2O7- + 8H+ 3RCOOH + 2Cr3+ + 4H2O

Reaction with Tollens:- Aldehydes +ve Silver Mirror Forms

Reaction with Benedicts:- Aldehydes + ve Blue (Cu2+) Red Precipitate (Cu+)

Reaction with Brady’s:(2,4 DNP or 2,4 DiNitroPhenylhydrazine)- Carbonyls +ve Orange Precipitate

Reaction with Iodine:- Methyl group adjacent to C=O +ve Pale Yellow Precipitate, Antiseptic smell

Melting point used to identify Carbonyl compound

Dissolved in Methanol & conc H2SO4

AgNO3 dissolved in NH3(aq)

Dissolved in NaOH

dil H2SO4

LiAlH4 (in Dry Ether) to go from Carb Acid to 1o or Aldehyde

Presence of Alkali

Triiodomethane

+ HCN Reactions

Propanone + HCN

Ethanal + HCN

2 methyl 2 hydroxypropanenitrile

2 hydroxypropanenitrile

Nucleophilic Addition

In a lab HCN made by reacting KCN(s) + H2SO4

+ Carboxylic Acids

H-Bonding in Pure Ethanoic Acid (Dimer Shape)

Sodium Ethanoate

Identifying Carboxylic Acids:Add Sodium Carbonate – effervescence if +ve

Weak acid – Partially Dissociate

Very soluble in H2OLonger chain, less soluble

Formed from:- Oxidising a 1°- Hydrolysis of Nitrile

(Reflux with dil HCl and distil off)

Reaction with PCl5:CH3COOH + PCl5 POCl3 + HCl + CH3COCl

Ethanoyl Chloride

Add NH3 white smoke = +ve

Acid + Alcohol Ester + H2O

+ Esters

Acid Hydrolysis:- Reflux with dil HCl or H2SO4

Transesterification

Base Hydrolysis:- Reflux with dil Alkali (e.g. NaOH)

Dicarboxylic Acid + Diol Alcohol Polyester

+ 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

+ Acyl ChloridesEthanoyl Chloride

Reaction with H2O:

CH3COCl(l) + H2O(l) CH3COOH(l) + HCl(g)

Reaction with Alcohol:

CH3COCl(l) + CH3CH2OH(l) CH3COOCH2CH3(l) + HCl(g) Ethyl Ethanoate

Reaction with Ammonia:

CH3COCl(l) + NH3(aq) CH3CONH2(aq) + HCl(g)

Ethanamide Reaction with Ethylamine:

CH3COCl(l) + C2H5NH2(aq) CH3CONHCH3CH2(aq) + HCl(g)

N-Ethyl-Ethanamide

N-“substituted”-Amide

-amide

+ Isomerism/Optical IsomersOnly occurs when chiral carbon present:

- Carbon with 4 different groups attached

Mirror

Enantiomers/Optical Isomers

Racemic Mixture:Contains equal amounts of each enantiomer

+ 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

+ Kp

+ Effects on EquilibriaAdding 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

+ 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

+

Arrhenius:

- Acids are H+ producers- Bases are OH- producers in H2O- Only used in aqueous solutions

Bronsted-Lowry:

- Acids are proton donors- Bases are proton acceptors

Acid Theories

A base has a lone pair of electrons which can form a dative covalent bond with a H+

Lewis:

- Acid is an electron pair acceptor- Bases is an electron pair donor

HA + H2O H3O+ + A-

Conjugate Pairs

H2O & HA are Acids & Bases as they give & accept H+

H+ = H3O+

HA is the acid & A- is it’s conjugate baseH2O is the base & H3O+ is it’s conjugate acid

Amphoteric Substances:• It acts a base or an acid H3O+ H2O OH-

AcidBase

+ pH Strong Acids or Strong BasespH = - log 10 [ H+ ] Kw @298k = 1x10

-14

[ H+ ] = 10-pH

+ pH Strong Acid & Strong Base

Excess [ H+ ]

Excess [ OH- ]

+ pH Weak AcidspKa = -log10( Ka )

Larger pKa = Weaker Acid