![+ 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](https://image.slidesharecdn.com/unit4a2chemistry-131016114317-phpapp01/85/Unit-4-A2-Chemistry-Notes-Edexcel-2-320.jpg)
![+ pH Strong Acids or Strong Bases
pH = - log 10 [ H+ ]
[ H+ ] = 10-pH
Kw @298k = 1x10-14](https://image.slidesharecdn.com/unit4a2chemistry-131016114317-phpapp01/85/Unit-4-A2-Chemistry-Notes-Edexcel-21-320.jpg)
![+ pH Strong Acid & Strong Base
Excess [ OH- ]
Excess [ H+ ]](https://image.slidesharecdn.com/unit4a2chemistry-131016114317-phpapp01/85/Unit-4-A2-Chemistry-Notes-Edexcel-22-320.jpg)
Unit 4 A2 Chemistry Notes Edexcel
- 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. +
- 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