dojo study club pure chem wa2 revision guide

Dojo Study Club Pure Chemistry WA2 Revision Guide

Definitions Exothermic Reaction A reaction in which heat (energy) is given out to the surroundings. Endothermic Reaction A reaction in which heat (energy) is absorbed by the surroundings. Enthalpy Change The overall heat change in a reaction. Activation Energy The minimum energy that reacting particles must possess in order for a chemical reaction to occur. Catalyst A substance that will increase the rate of a reaction by lowering the activation energy. Once activation Energy is lowered, more reacting particles have energy greater or equal to the activation Energy. Haber Process An industrial application for the production of ammonia. Rate of Reaction

Electrolysis The process of using electricity to break down or decompose a compound. Electrolyte A molten or aqueous compound that conducts an electric current. Electrode A metal or carbon rod by which the current leaves or enters the electrolyte. Inert Electrode Electrodes that do not react with the products of electrolysis. Non-Electrolytes Substances that do not conduct electricity under any conditions. Electroplating The deposition of a thin layer of metal on an object, by means of electrolysis. Simple Cell A device that converts chemical energy into electrical energy. Electrolysis

Endothermic Exothermic ΔH = BB - BF enthalpy change = bonds breaking - bonds forming ΔH = BB - BF enthalpy change = energy absorbed to break bonds - energy released to form bonds Cheat Sheet energy profile diagram energy level diagram (ΔH) (ΔH)

Rate Of Reaction The speed at which reactants are converted into products, per unit time Concentration Higher concentration, more particles per unit volume, higher frequency of efficient collisions.(aqueous solutions) Temperature Higher temperature, particles move faster with more energy, higher frequency of efficient collisions(all) Pressure Higher pressure, particles closer to one another, higher frequency of efficient collisions(gases) Surface Area Smaller particles, larger surface area, higher frequency of efficient collisions(solids) Endothermic Exothermic

Electrolysis Electrochemistry Chemical Celldoes it have a battery? Molten most simple, only 2 ions present in this case, NaCl is the electrolyte. Na+ and Cl- are the ions Anode: Cl- discharged Cathode: Na+ discharged Dilute 4 ions present Na+, Cl-, H+, OH- Ions chosen based on ease of discharge Anode: OH- discharged Cathode: H+ discharged Concentrated 4 ions present Na+, Cl-, H+, OH- Ions chosen based on ease of discharge (concentrated) Anode: Cl- discharged Cathode: H+ discharged Concentrated in concentrated electrolytes, the ease of discharge of anions change. Halogens > OH- Generally, Cations: less reactive = easier discharge Anions: OH- > Halogens > Others Simple Electric Cell chemical energy > electric energy electric energy > chemical energy a more reactive metal is preferientially oxidised. Anode: More Reactive Metal (Zinc) Cathode: Less Reactive Metal (Copper) The more reactive metalʼs electrons would flow to the less reactive metal, creating a potential difference. The further apart the 2 metals are on the reactivity series, the greater the voltage. Electrolyte must always be aqueous. Red Cat And Ox Reduction at Cathode Oxidation at Anode (for all electrochemistry)

Cation Table The observations with NaOH(aq) and NH3 (aq) are the same for Al3+ and Pb2+ ions Add Potassium Iodide (KI) to both solutions. A yellow precipitate (PbI2) is formed for Pb, while no precipitate formed for Al How to differentiate between Al and Pb

Salt Solution Light Blue pptWhite ppt Green ppt Red-brown ppt Al, Ca, Pb, Zn Cu Fe2+ Fe3+ Soluble Al, Pb, Zn Insoluble Ca Salt Solution Light Blue pptWhite ppt Green ppt Red-brown ppt Al, Pb, Zn Cu Fe2+ Fe3+ Soluble Zn Insoluble Al, Pb Deep Blue sol Cu No ppt NH4+ No ppt Ca2+ or NH4+ NaOH (aq) NH₃ (aq) Cation Table in excess in excess

Anion Table To remove carbonates and hydroxide ions! If dilute nitric acid is not added, precipitates of BaCO3 , Ag2CO3 and AgOH will form when barium nitrate / silver nitrate is added, which will interfere with the results. Sulfates, Chlorides and Iodides require Dilute Nitric Acids - Why?

Salt Solution NH3 Gas CO2 Gas White ppt White ppt CO32- NO3- SO42- Cl- No ppt I- Anion Table + HCl (aq) + NaOH (aq) and Al (s), heat + HNO3 (aq) and Ba(NO3)2 (aq) + HNO3 (aq) and AgNO3 (aq)