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CHEMISTRY (PAPER 2) Chemical change ................................................................................................................................................................................. 3 Endothermic and Exothermic Reactions ........................................................................................................................................ 3 Rate of Reactions ............................................................................................................................................................................ 4 Collision Theory .......................................................................................................................................................................... 4 Reaction Rate ............................................................................................................................................................................. 4 Measuring Rate .......................................................................................................................................................................... 4 Boltzmann Distribution of energy .................................................................................................................................................. 5 Equilibrium ..................................................................................................................................................................................... 6 Open and closed systems ........................................................................................................................................................... 6 Reversable Reactions ................................................................................................................................................................. 6 Dynamic Equillibrium ................................................................................................................................................................. 6 Le Chatelier’s Principal ............................................................................................................................................................... 6 Equilibrium Constant (KC) ........................................................................................................................................................... 6 KW ............................................................................................................................................................................................... 7 KA ................................................................................................................................................................................................ 7 Electrochemical Reactions .................................................................................................................................................................. 8 Voltaic or Galvanic ..................................................................................................................................................................... 8 Electrolytic ...................................................................................................................................................................................... 9 Definitions ...................................................................................................................................................................................... 9 Standard Hydrogen Electrode ...................................................................................................................................................... 10 Organic Chemistry ............................................................................................................................................................................. 11 Naming Organic Molecules (IUPAC Names) ................................................................................................................................. 11 Dienes....................................................................................................................................................................................... 12 Alcohols .................................................................................................................................................................................... 13 Aldehydes ................................................................................................................................................................................. 14 Ketones .................................................................................................................................................................................... 14 Carboxylic Acid ......................................................................................................................................................................... 14 Haloalkanes .............................................................................................................................................................................. 14 Esters ........................................................................................................................................................................................ 14 Addition Reactions ....................................................................................................................................................................... 15 Hydrohalogenation .................................................................................................................................................................. 15 Halogenation ............................................................................................................................................................................ 15 Hydration ................................................................................................................................................................................. 15 Hydrogenation ......................................................................................................................................................................... 15 Elimination Reactions ................................................................................................................................................................... 15 Dehydrohalogentaion .............................................................................................................................................................. 15 © Samir Daniels Chemistry Page 1 Dehydration ............................................................................................................................................................................. 15 Cracking .................................................................................................................................................................................... 15 Substitution Reactions .................................................................................................................................................................. 15 Interconversion ........................................................................................................................................................................ 15 The Chemical Industry ...................................................................................................................................................................... 16 SASOL ............................................................................................................................................................................................ 16 Hydrocracking .......................................................................................................................................................................... 16 Steam cracking ......................................................................................................................................................................... 16 Fractional distillation ................................................................................................................................................................ 16 The Chloralkali Industry .................................................................................................................................................................... 16 Uses .............................................................................................................................................................................................. 16 The Fertiliser Industry ....................................................................................................................................................................... 17 Manufacturing .............................................................................................................................................................................. 17 Batteries ............................................................................................................................................................................................ 17 Leclanché dry cell ......................................................................................................................................................................... 17 Zinc chloride dry cell ..................................................................................................................................................................... 17 Alkaline dry cell............................................................................................................................................................................. 17 Mercury Battery ........................................................................................................................................................................... 17 Lithium Ion Battery ....................................................................................................................................................................... 17 Lead-acid storage battery ............................................................................................................................................................. 17 Data booklet ..................................................................................................................................................................................... 18 © Samir Daniels Chemistry Page 2 CHEMICAL CHANGE ENDOTHERMIC AND EXOTHERMIC REACTIONS For an endothermic reaction: o The temperature of the surroundings decreases because the kinetic energy is being transferred to break bonds. o The temperature decreases because it takes in energy. o Temperature: T ↓ o Bond energy: E ↑ ΔH>0 (Positive) o Here the graph shows that it takes more energy to break bonds than to make bonds. For an exothermic reaction: o Temperature of the surroundings increase because making bonds create energy o E↓ o T↑ The activated complex is the nature when all bonds between the reactants have been broken, before any bonds of the products have been created. The activation energy (𝐸𝐴 ) is the amount of energy required to break all bonds before a chemical reaction can take place. The reactants need sufficient 𝐸𝐾 to bring upon a chemical reaction. © Samir Daniels Chemistry Page 3 RATE OF REACTIONS COLLISION THEORY Particles can only react when they are in contact with one another. The reaction rate is therefore determined by the number of and frequency of the collisions that is made REACTION RATE The reaction rate is the speed at which a reaction takes place Factors that affect rate of reactions: O Surface area (of a solid) A greater surface area increases the likelihood of a molecule colliding and reacting ↑ S.A - ↑reaction rate O Concentration (of a solution) Higher concentration means there are more reactant molecules per unit of volume, which means that molecules find it easier to collide with the substance ↑ Concentration – ↑ reaction rate O Pressure (of a gas) Easier to collide ↑ Concentration – ↑ reaction rate O Temperature An increase in temperature means the molecules’ speed increase and will increase the number of collisions per second O Addition of a catalyst The catalyst holds the molecule into place until another molecule reacts with is. Adding a catalyst – ↑ reaction rate O Nature of reactants The dotted line shows the increased reaction rate. MEASURING RATE Change in temperature Change in colour Change in mass of the reaction vessel Measuring gas volumes (Pressure gauge) Turbidity (precipitate formed) vs. time © Samir Daniels Chemistry Page 4 C HANGE IN M ASS C HANGE IN VOLUME Measured using a scale Measure the mass of the reaction vessel. Measured using a gas syringe or pressure gauge BOLTZMANN DISTRIBUTION OF ENERGY The very hot particles (at the end) will escape 1 and the 𝐸𝐾 will decrease because only the cooler (particles with less 𝐸𝐾 will be left over. 1 Change state © Samir Daniels Chemistry Page 5 EQUILIBRIUM OPEN AND CLOSED SYSTEMS A system in which both energy and matter can be changed with surrounding is called an open system. A system in which only energy but not matter can be exchange with the surrounding is called a closed system. REVERSABLE REACTIONS 𝐴+𝐵 ⇌𝐶+𝐷 In a chemical equilibrium, the concentrations of reactants and products do not change. But the forward and reverse reactions have not stopped - they are still going on at the same rate as each other. DYNAMIC EQUILLIBRIUM A dynamic equilibrium is a chemical equilibrium between a forward reaction and the reverse reaction where the rate of the reactions are equal. LE CHATELIER’S PRINCIPAL When the conditions (temperature, concentration or pressure) under a closed system is disturbed, the system acts in such a way as to oppose the change. The equilibrium shifts in the direction that opposed it. → If the temperature increases, the system will try to get colder Three possible changes can upset the equilibrium: Temperature o Decrease in temperature will favour the exothermic reaction Concentration o If the concentration is increased, the equilibrium shifts in the opposite direction (away from) Pressure o A decrease in pressure will favour the reaction which has an increase in volume EQUILIBRIUM CONSTANT (KC ) For the reaction: aA + bB ⇌ cC + dD a → No. of Moles (balancing number) A → Molecule KC = [C]c [D]d [A]a [B]b [A] means the concentration of A Only molecules in the liquid phase i.e. no solids No H2O If KC > 1 then it Favours Product If KC < 1 then it favours the Reactant © Samir Daniels Chemistry Page 6 S OLVING K C P ROBLEMS 1. 2. Write out full balanced equation Construct nstart , nreacted , nequilibrium , concentration table` 3. 4. Fill in all known values See what the question is asking and solve. aA a No. of moles nstart nreact nequilibrium Concentration +bB b This goes with the ratio coefficients C= ⇌ cC c nstart − nreact n v If the products (C and D) are higher, i.e. K C > 1, it will favour the products K C is affected by: o Temperature o Pressure (gas) NH3 used as fertilizers and cleaning products Production can be sped up by lowering temperature or increasing H 2 or N2 +dD d KW K W measures how easily H2O splits up into H+ and OH- ions H2 O ⇌ H+ + OH(hydrogen Ion) (Hydroxide Ion) 2H2 O ⇌ H3 O+ + OH- (Hydronium) If a chemical releases more H+ ions into a solution, it is an ACID 1 × 10−3 [H+ ] ≡ pH of 3 Acidic Adding OH- will shift the equilibrium to the left, producing less H+ ions KW > 7 Alkali K W = [H3 O+ ][OH- ] = [H+ ][OH- ] = 1 × 10−14 o ∴ [H+ ] = 1 × 107 − log(1 × 107 ) = 7 = pH of H+ in H2 O KA Acid Dissociation Constant All acids donate H+ ions o Monotropic o Can only donate one hydrogen o o © Samir Daniels Chemistry Page 7 Because this area has a big area of negative charge, the H+ ion does not dissociate easily, which means it is not a strong acid. ELECTROCHEMICAL REACTIONS VOLTAIC OR GALVANIC Converts chemical energy into electrical energy Dipped in an electrolyte o Zn|Zn2+ ||Ag+ |Ag Anode first Oxidation is written on the left o Zn → Zn2+ + 2eReduction is on the right o o Ag+ + e- → Ag Zn + Ag+ + e- → Ag + Zn2+ + 2e- C ALCULATE E 0 C ELL : 1. Identify two half reactions 2. Write the most positive one above the other 3. Draw around them Top is forward reaction (ANODE) Bottom is reverse reaction (CATHODE) 4. Identify oxidation or reduction 5. Solve Solid|Aqueous||Aqueous|Solid © Samir Daniels Chemistry Page 8 STANDARD CONDITIONS: 1 atm (gasses) 1 M (solutions) 25° C (temp) (298K) Otherwise 𝑝𝑉 = 𝑛𝑅𝑇 ELECTROLYTIC Converts electrical energy into chemical potential energy Electrode reactions sustained by a supply of electrical energy For the electrode to become positive i.e. if you want the negatively charged ion to be attracted to the electrode, attach it to the positive terminal O e- gets sucked away from the electrode attached to the +ve terminal. O O − 𝐴2+ 𝑎𝑞 + 2𝑒 → 𝐴𝑠 𝐵(𝑠) → 2+ 𝐵(𝑎𝑞) + 2𝑒 Reduction − Oxidation Electrorefining DEFINITIONS OXIDATION: LOSS OF ELECTRONS happens at the ANODE REUCTION: GAIN OF ELECTRONS happens at the CATHODE Mass of cathode ↑ Mass of anode ↓ AN OX Anode → Oxidation RED CAT REDuction → CAThode OIL RIG Oxidation if Lost / Reduction if Gain Oxidant (Oxidising agent) – causes another to be oxidised, which means it gains electrons Reductant (Recuing agent) – causes another to be reduced, which means is loses electrons. © Samir Daniels Chemistry Page 9 STANDARD HYDROGEN ELECTRODE H2 O → H+ + OH2H+ + 2e- → H2(g) OH- + Na+ → NaOH © Samir Daniels Chemistry Page 10 ORGANIC CHEMISTRY The chemistry of carbon NAMING ORGANIC MOLECULES (IUPAC NAMES) *Alphabetical Preference No. of Carbon 1 Name Meth- 2 Eth- 3 Prop- 4 But- 5 Pent- 6 Hex- 7 Hept- 8 Oct- 9 Non- 10 Dec- Single Bonds between Carbon –ane Structure Alkanes 𝐶𝑛 𝐻2𝑛+2 Double bonds between Carbons –ene Triple bonds between Carbons –yne Alkenes 𝐶𝑛 𝐻2𝑛 Alkynes 𝐶𝑛 𝐻2𝑛−2 © Samir Daniels Chemistry Page 11 When finding the name of a molecule, 1. 2. 3. Identify the longest chain of carbons2. Locate3 any double or triple bonds Locate any additional substituents4 There’s only one Carbon → MethThere’s 2 chlorines → dichlorIt’s single bonds → -ane o Dichloromethane Alkane + O2 → H2O + CO2 Δ H < 0 (exothermic) DIENES Conjugated o Separated by a single bond o Cumulated o Two double bonds to one carbon o but-2,3- diene Isolated o More than one saturated carbon bonds between two double bonds o hex-2,4-diene but-1,4-diene Homogolous Series → a group of compounds with the same general formula 2 Gives you the root (meth-, eth- ) Numbered position 4 Something extra (clhoro-) 3 © Samir Daniels Chemistry Page 12 Isomers → different structure, but same empirical formula The longer the chain of Carbon, the higher the fixed points (melting and boiling points) Stronger inter-molecular forces will have high boiling points (more energy to break bonds) Functional series → double or triple bonds are functional groups. They are ‘add-ons’ that change the chemistry of a carbon chain ALCOHOLS Suffix -ol Methanol Ethanol Hex-3,3-diol T YPES OF ALCOHOLS Primary Alcohol Secondary Alcohol Tertiary Alcohol The number of carbons surrounded by the hydroxide determines the type of alcohol. © Samir Daniels Chemistry Page 13 ALDEHYDES Suffix Methanal Butanal Prop-2-one Hex-2,3-dione Methanoic acid Pentanoic acid -al KETONES Suffix -one CARBOXYLIC ACID Suffix: -ic acid HALOALKANES Prefix: Where X is any halogen (Chlorine, Fluorine, Bromine, etc) halo- chloro- fluoro- Flouroethane 2-bromo-1,3-dichloropentane Tetrachloromethane Alcohol + carboxylic acid → ester + water Ethanol + Butanoic acid → butyl ethanoate + water Methanol + Hexanoic acid → hexyl methanoate ESTERS An ester is the product of an alcohol and a carboxylic acid Done under acidic conditions Saturated → alkane bonds, where carbons make one bond only Unsaturated → carbons have more than one bond © Samir Daniels Chemistry Page 14 ADDITION REACTIONS Unsaturated compounds undergo addition reactions HYDROHALOGENATION HX + alkene o Hydrochloric acid + but-1-ene → butyl-1-chloride → + HALOGENATION X2 + alkene o F2 + But-1-ene → butyl-1,2-difluoride → + HYDRATION H2O + alkene → Alcohol o But-1-ene + water → butan-1-ol o + → HYDROGENATION H2 + alkene → Alkane o But-1-ene + Hydrogen gas → butane o + → ELIMINATION REACTIONS Saturated compounds undergo elimination reactions DEHYDROHALOGENTAION Elimination of HX from a haloalkane Heat under reflux in a concentrated solution of NaOH or KOH SUBSTITUTION REACTIONS INTERCONVERSION DEHYDRATION Elimination of H2O from an alcohol Heating of alcohol with excess concentration H2SO4 Tertiary alcohols only Just add HX to produce a haloalkane Reactions of bases with haloalkanes (hydrolysis) produces alcohols Haloalkanes from alkanes CRACKING Or low pressure and temperature with catalyst Breaking up large hydrocarbon molecules into smaller and more useful bits High pressure and temperature without catalyst © Samir Daniels Chemistry Page 15 THE CHEMICAL INDUSTRY SASOL Use Coal Gasification to produce liquid fuels HYDROCRACKING Hydrocracking is a cracking process that is assisted by the presence of an elevated partial pressure of hydrogen gas. It produces chemical products such as ethane, LPG, isoparaffins, jet fuel and diesel. STEAM CRACKING Steam cracking occurs under very high temperatures. During the process, a liquid or gaseous hydrocarbon is diluted with steam and then briefly heated in a furnace at a temperature of about 850°. Steam cracking is used to convert ethane to ethylene. Ethylene is a chemical that is needed to make plastics. Steam cracking is also used to make propylene, which is an important fuel gas. FRACTIONAL DISTILLATION Fractional distillation is the separation of a mixture into its component parts, or fractions. Since air is made up of a number of gases (with the major component being nitrogen), fractional distillation can be used to separate it into these different parts THE CHLORALKALI INDUSTRY Production of Chlorine and Sodium Hydroxide Through the electrolysis of sodium chloride (NaCl) – saturated in the form of brine. USES Chlorine is used to purify watrer Cleaning agent The membrane cell: © Samir Daniels Chemistry Page 16 THE FERTILISER INDUSTRY A fertiliser is a compound that is given to a plant to promote growth. Fertilisers usually provide the three major plant nutrients and most are applied via the soil so that the nutrients are absorbed by plants through their roots. NPK Ratio is the percentage of nitrogen, phosphorous and potassium in the fertiliser MANUFACTURING Ammonia → Haber Process Nitric Acid → Ostwald Process Sulphuric Acid → Contact process Pg 195 Everything Science. BATTERIES LECLANCHÉ DRY CELL Zinc-carbon dry cell The electrolyte consists of an ammonium chloride paste Electrodes are made of zinc and carbon Zinc forms the anode Manganese forms the cathode Powdered carbon is used in the cathode to improve conductivity and retain moisture Anode: 𝑍𝑛 → 𝑍𝑛2 + + 2𝑒 − Cathode: 2𝑁𝐻4+ + 2𝑀𝑛𝑂2 + 2𝑒 − → 𝑀𝑛2 𝑂3 + 2𝑁𝐻3 + 𝐻2 𝑂 ZINC CHLORIDE DRY CELL Zinc-carbon dry cell Electrolyte is zinc chloride Manganese forms the cathode ALKALINE DRY CELL MERCURY BATTERY LITHIUM ION BATTERY Potassium hydroxide as the electrolyte Lasts much longer than dry cells LEAD-ACID STORAGE BATTERY Small battery used in watches Zinc anode Steel cathode 12V used in cars Contains six cells connected in series Led anode Lead oxide cathode © Samir Daniels Chemistry Page 17 Lithium ions move back and forth between positive and negatie electrodes Can be recharged DATA BOOKLET Standard pressure Pθ 1,013 x 105 Pa Molar gas volume at STP Vm 22,4 dm3∙mol-1 Standard temperature Tθ 273 K n m M q=It c m n or c V MV Eθcell Eθcathode Eθanode θ Eθcell Ereduction Eθoxidation W = Vq θ Eθcell Eθoxidisingagent Ereducing agent © Samir Daniels Chemistry Page 18