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Hard or Soft Combustion Ammonia Energy level diagrams Analysing substances Endothermic and exothermic reactions 04/05/2017 Step 1: Energy must be SUPPLIED to break bonds: Step 2: Energy is RELEASED when new bonds are made: A reaction is EXOTHERMIC if more energy is RELEASED then SUPPLIED. If more energy is SUPPLIED then is RELEASED then the reaction is ENDOTHERMIC Energy level diagrams 04/05/2017 Energy level Activation energy Using a catalyst might lower the activation energy Energy given out by reaction Reaction progress Exothermic vs endothermic: 04/05/2017 EXOTHERMIC – more energy is given out than is taken in (e.g. burning, respiration) ENDOTHERMIC – energy is taken in but not necessarily given out (e.g. photosynthesis) Burning Methane CH4 + 2O2 To burn methane you have to break all of these bonds: And then you have to make these ones: 2H2O + CO2 04/05/2017 Burning Methane CH4 + 2O2 04/05/2017 2H2O + CO2 Methane Oxygen Carbon dioxide Water Bond energies 04/05/2017 C-H = 435 Kj O=O = 497 Kj Total for breaking bonds = 4x435 + 2x497 = 2734 KJ/mol C=O = 803 Kj H-O = 464 Kj Total for making bonds = 2x803 + 4x464 = 3462 KJ/mol Total energy change = 2734-3462 = -728 KJ/mol Drawing this on an energy diagram: 04/05/2017 2734 Kj 3462 Kj -728 Kj More energy is given out (3462) than is given in (2734) – the reaction is EXOTHERMIC. The total (“nett”) energy change is –728 Kj. An endothermic reaction would have a positive energy change. Bond energy values C-H = 435 KJ/mol O-H = 464 KJ/mol O=O = 497 KJ/mol C=O = 803 KJ/mol C-O = 360 KJ/mol C-C = 346 KJ/mol 04/05/2017 Burning Methanol 2CH3OH + 3O2 Total for breaking bonds = 6x435 (C-H) + 2x360 (C-O) + 2x464 (O-H) + 3x497 (O=O) = 5749 KJ/mol 04/05/2017 2CO2 + 4H2O Total for making bonds = 4x803 (C=O) + 8x464 (O-H) = 6924 KJ/mol Energy change = 5749-6924 (divide this by two as we are dealing with two molecules of methanol) = -587.5 KJ/mol 04/05/2017 Click here and return to the “Big Picture!” Reversible Reactions 04/05/2017 Some chemical reactions are reversible. In other words, they can go in either direction: A + B e.g. Ammonium chloride NH4Cl C + D Ammonia + hydrogen chloride NH3 + HCl If a reaction is EXOTHERMIC in one direction what must it be in the opposite direction? For example, consider copper sulphate: Hydrated copper sulphate (blue) + Heat CuSO4.5H2O Anhydrous copper sulphate (white) CuSO4 + H2O + Water Reversible Reactions 04/05/2017 When a reversible reaction occurs in a CLOSED SYSTEM (i.e. no reactants are added or taken away) an EQUILIBRIUM is achieved – in other words, the reaction goes at the same rate in both directions: A + B Endothermic reactions Increased temperature: A + B C + D C + D Exothermic reactions Increased temperature: A + B C + D More products Less products Decreased temperature: Decreased temperature: A + B C + D Less products A + B C + D More products Making Ammonia 04/05/2017 Guten Tag. My name is Fritz Haber and I won the Nobel Prize for chemistry. I am going to tell you how to use a reversible reaction to produce ammonia, a very important chemical. This is called the Haber Process. Nitrogen + hydrogen Ammonia N2 + 3H2 2NH3 Fritz Haber, 1868-1934 To produce ammonia from nitrogen and hydrogen you have to use three conditions: Nitrogen Hydrogen •High pressure •450O C •Iron catalyst Mixture of NH3, H2 and N2. This is cooled causing NH3 to liquefy. Recycled H2 and N2 Uses of Ammonia 04/05/2017 Ammonia is a very important chemical as it can be used to make plant fertilisers and nitric acid: Ammonia gas Oxygen Hot platinum catalyst Nitrogen monoxide Cooled Nitrogen monoxide Water and oxygen Nitric acid More ammonia can then be used to neutralise the nitric acid to produce AMMONIUM NITRATE (a fertiliser rich in nitrogen). Ammonia + nitric acid NH3 + HNO3 Ammonium nitrate NH4NO3 The trouble with nitrogen based fertilisers is that they can also create problems – they could contaminate our drinking water. Haber Process: The economics 04/05/2017 A while ago we looked at reversible reactions: Endothermic, increased temperature A + B Endothermic C + D Exothermic, increase temperature A + B Nitrogen + hydrogen Ammonia N2 + 3H2 2NH3 C + D Exothermic 1) If temperature was DECREASED the amount of ammonia formed would __________... 2) However, if temperature was INCREASED the rate of reaction in both directions would ________ causing the ammonia to form faster 3) If pressure was INCREASED the amount of ammonia formed would INCREASE because there are less molecules on the right hand side of the equation Haber Process Summary 04/05/2017 A low temperature increases the yield of ammonia but is too slow A high temperature improves the rate of reaction but decreases the yield too much A high pressure increases the yield of ammonia but costs a lot of money To compromise all of these factors, these conditions are used: Nitrogen Hydrogen •200 atm pressure •450O C •Iron catalyst Mixture of NH3, H2 and N2. This is cooled causing NH3 to liquefy. Recycled H2 and N2 04/05/2017 Click here and return to the “Big Picture!” Periodic table timeline 22 of 47 © Boardworks Ltd 2005 Mendeleev and the periodic table Mendeleev created the first modern periodic table by grouping together elements with similar properties. 23 of 47 © Boardworks Ltd 2005 Arranging elements into columns When elements are arranged according to their properties what patterns do you see? hydrogen is a special case H He Li Be B C N O F Ne Na Mg Al Si P S Cl Ar K reactive metals reactive gases unreactive gases Similar elements go into the same columns. Hydrogen is an exception – it is best positioned above the reactive metals. 24 of 47 © Boardworks Ltd 2005 The periodic table Arranging all the elements by their atomic number and their properties led to the creation of… H …the periodic table He Li Be B C N O F Ne Na Mg Al Si P S Cl Ar K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn Fr Ra Ac Rf Db Sg Bh Hs Mt Ds Rg ? ? ? ? ? ? ? 25 of 47 © Boardworks Ltd 2005 Patterns: reactivity of metals What happens to the reactivity of metals along a period? What happens to the reactivity of metals down a group? increase in reactivity Which is the most reactive metal? Li Be Na Mg Al K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po Fr Ra Ac Rf Db Sg Bh Hs Mt Ds Rg increase in reactivity 26 of 47 © Boardworks Ltd 2005 Patterns: reactivity of non-metals Group 0 elements are the most unreactive of all elements. For the remaining non-metals and metalloids, reactivity increases up a group and along a period from left to right. 27 of 47 increase in reactivity Which is the most reactive non-metal/ metalloid? increase in reactivity He B C N O F Ne Si P S Cl Ar unreactive Ge As Se Br Kr Sb Te I Xe At Rn © Boardworks Ltd 2005 Patterns, atomic number and electrons The periodic table shows that patterns in the properties of elements are linked to atomic number. H Li Be Na Mg What links atomic number and the properties of elements? electrons He B C N O F Ne Al Si P S Cl Ar K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn Fr Ra Ac Rf Db Sg Bh Hs Mt Ds Rg ? ? ? ? ? ? ? 28 of 47 © Boardworks Ltd 2005 Atomic number and electrons The properties of elements are hugely influenced by the number and arrangement of electrons in the atom. What links atomic number and the number of electrons in an atom? atomic number = number of protons number of protons = number of electrons atomic number = number of electrons As atomic number increases by one, the number of electrons also increases by one. This means that the elements in the periodic table are also arranged in order of the number of electrons. 29 of 47 © Boardworks Ltd 2005 Electron shells Electrons are arranged in shells around an atom’s nucleus. Each shell has a maximum number of electrons that it can hold. Electrons will fill the shells nearest the nucleus first. 1st shell holds a maximum of 2 electrons 2nd shell holds a maximum of 8 electrons 3rd shell holds a maximum of 8 electrons This electron arrangement is written as 2,8,8. 30 of 47 © Boardworks Ltd 2005 Electrons in period 1 Elements in period 1 only have electrons in the first shell. Why are there only two elements in period 1? 1 1 2 3 4 5 6 7 0 H He 1 2 The first shell can only hold a maximum of two electrons, so period 1 only includes the elements hydrogen and helium. What is special about the outer shell of helium? 31 of 47 © Boardworks Ltd 2005 Electrons in period 2 Elements in period 2 all have a complete first shell. What happens to electrons in the second shell in period 2? 2 1 2 3 4 5 6 7 0 Li Be B C N O F Ne 2,1 2,2 2,3 2,4 2,5 2,6 2,7 2,8 The second shell is completed one electron at a time going across the period from left to right. What is special about the outer shell of neon? 32 of 47 © Boardworks Ltd 2005 Electrons in period 3 Elements in period 3 have complete first and second shells. What happens to electrons in the third shell in period 3? 1 3 2 Na Mg 3 4 5 6 7 0 Al Si P S Cl Ar 2,8,4 2,8,5 2,8,6 2,8,7 2,8,8 2,8,1 2,8,2 2,8,3 The third shell is completed one electron at a time going across the period from left to right. What is special about the outer shell of argon? 33 of 47 © Boardworks Ltd 2005 Patterns of electron arrangements Consider the electron arrangements of the first 20 elements in the periodic table. 1 2 3 4 5 6 7 0 2 1 1 2 2,1 2,2 2,3 2,4 2,5 2,6 2,7 3 2,8,1 2,8,2 2,8,3 2,8,4 2,8,5 2,8,6 2,8,7 2,8,8 4 2,8,8,1 2,8,8,2 2,8 What is the pattern of outer shell electrons in a group? What is the pattern of outer shell electrons across a period? What is the pattern of full electron shells in a group? 34 of 47 © Boardworks Ltd 2005 Electron trends in the periodic table Trends down a group: the number of outer shell electrons is the same; the number of complete electron shells increases by one. The number of a group is the same as the number of electrons in the outer shell of elements in that group, except for group 0. Trends across a period: the number of outer shell electrons increases by one; the number of complete electron shells stays the same. The point at which a new period starts is the point at which electrons begin to fill a new shell. 35 of 47 © Boardworks Ltd 2005 What’s the electron arrangement? 36 of 47 © Boardworks Ltd 2005 Names of groups in the periodic table 37 of 47 © Boardworks Ltd 2005 Glossary atomic number – The number of protons in an atom. 38 of 47 Sometimes called the proton number. electron arrangement – A shorthand way of writing the number of electrons in an atom’s electron shells. element – A substance made up of only one type of atom. group – A column in the periodic table containing elements with the same number of outer shell electrons and similar chemical properties. period – A row in the periodic table containing elements with the same number of full electron shells. periodic table – The table that lists all the elements in order of increasing atomic number, arranged into groups and periods. property – Any characteristic of an element. © Boardworks Ltd 2005 04/05/2017 Click here and return to the “Big Picture!” Alcohols Alcohols are a group of organic molecules which contain oxygen. They form a HOMOLOGOUS series. Naming the Alcohols The names of alcohols follow the same pattern as the alkanes and alkenes. The first part of the name relates to the number of carbons in the chain. The second part of the name is -anol 1 carbon Butanol. 2 carbons Methanol 3 carbons Pentanol 4 carbons Ethanol 5 carbons Propanol Alkanes Alkenes Alcohols CnH2n+2 CnH2n CnH2n+1OH C2H4 C3H6 C4H8 C5H10 CH3OH C2H5OH C3H7OH C4H9OH C5H11OH CH4 C2H6 C3H8 C4H10 C5H12 Formula of Alcohols All alcohols have the formula; CnH2n+1OH Methanol Ethanol Propanol CH3OH C2H5OH C3H7OH Structure of Alcohols C – 4 bonds H – 1 bond O – 2 bonds (must be between a C and an H) Methanol H H C O H H H H H C C H H Ethanol O H Properties of Alcohols • They are FLAMMABLE/NOT FLAMMABLE • Their density (heaviness) INCREASES/DECREASES as the number of carbons increases • SOME/ALL of them are poisonous Click here for news story Alcohols: ■ dissolve in water to form a neutral solution ■ react with sodium to produce hydrogen ■ burn in air ■ are used as a fuels and solvents, and ethanol is the main alcohol in alcoholic drinks Carboxylic Acids Carboxylic Acids Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings 51 Carboxylic Acids Ethanol can be oxidised to ethanoic acid, either by chemical oxidising agents or by microbial action. Ethanoic acid is the main acid in vinegar. 52 Carboxylic Acids A carboxylic acid • Contains a carboxyl group, which is a carbonyl group (C=O) attached to a hydroxyl group (—OH). • Has the carboxyl group on carbon 1. O CH3 — C—OH or CH3COOH 53 Models of Carboxylic Acids • The three-dimensional models show the geometry of atoms in carboxylic acid molecules. Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings 54 Common Carboxylic Acids Methanoic acid (formic acid) O ║ H ─ C─ OH ethanoic acid (acetic acid) O ║ CH3─ C ─ OH Draw propanoic acid! 55 Acidity of Carboxylic Acids Carboxylic acids • dissolve in water to produce acidic solutions • ■ react with carbonates to produce carbon dioxide • ■ do not ionise completely when dissolved in • water and so are weak acids • ■ aqueous solutions of weak acids have a higher pH value than aqueous solutions of strong acids with the same concentration 56 Esters Esters and Naming Esters Carbolic acids react with alcohols in the presence of an acid catalyst to produce esters 57 Esters In an ester, • The H in the carboxyl group is replaced with an alkyl group. O CH3 — C—O—CH3 ester group 58 Esterification is • The reaction of a carboxylic acid and alcohol in the presence of an acid catalyst to produce an ester. O CH3—C—OH + H—O—CH2—CH3 O CH3—C—O—CH2—CH3 + H2O ethyl ethanoate (an ester) 04/05/2017 Click here and return to the “Big Picture!” The Water Cycle Water Water Treatment Made safe to drink by removing solids and micro-organisms Water source Filter solids Sedimentation of small particles using Aluminium sulphate Filter of fine sand Chlorine used to disinfect Distillation = PURE WATER Carbon reduces Cl levels Ion exchange resin Silver discourage bacterial growth on filter Ca2+ hard water Mg2+ Ca2+ Mg2+ soft water lather hard water SCUM Ions not removed by water purification Ca2+ Mg2+ Ca2+ Stearate Mg2+ Calcium ions from water + Stearate ions from soap (Soluble) (Soluble) Calcium Stearate (Insoluble) SCUM Types of hard water Temporarily Hard Co2 Limestone Ca2+ Soluble Calcium Hydrogencarbonate CaCO3(s) + CO2(g) + H2O(l) Ca(HCO3)2(aq) Ca(HCO3)2 Heat Scum Ca(HCO3)2(aq) CaCO3(s) + CO2(g) + H2O(l) Limescale Types of hard water Permanently Hard Gypsum Anhydrite Calcium Sulphate Heat Cannot be softened by heating CaSO4(aq) Removing hardness from water Ca2+ Mg2+ Na2CO3 Sodium Carbonate Calcium ions + Sodium Carbonate Sodium ions + Calcium Carbonate Install a water softener Ion exchange column contains resins Ca2+ Mg2+ Exchanged for Na+ Install a water softener Na+ Water Hard Water Soft water easy lather Hard water less lather Contains Mg2+ and Ca2+ ions, dissolved when water passes through rocks SCUM When hard water reacts with soap. SCALE When hard water is heated. SCALE is basically limescale which is Calcium Carbonate which is a solid ppt and forms on metal appliances reducing efficiency. +ve - Ca for bones/teeth -ve - Kettles furrow up less efficient Water Removing Hard Water Use washing soda Add Sodium Carbonate Precipitates out the Ca and Mg ions to form insoluble carbonates Ion Exchange (water softener) Filled with resin. Contain Sodium/Hydrogen Ions As the water is passed through the resin, the Na/H ions are EXCHANGED with the Ca/Mg ions. Needs to be topped up with Na ions so NaCl is poured in to replenish. 04/05/2017 Click here and return to the “Big Picture!” Flame colour Lithium Flame colour Bright red Flame colour sodium Flame colour Yellow Flame colour potassium Flame colour lilac Flame colour calcium Flame colour Red Flame colour barium Flame colour green Test for carbonates Carbonates react with dilute acids to form Test for carbonates Carbon dioxide, carbon dioxide turns limewater milky Precipitation with sodium hydroxide Aluminium, calcium and magnesium ions form Precipitation with sodium hydroxide white precipitates Precipitation with sodium hydroxide Aluminium hydroxide precipitate dissolves Precipitation with sodium hydroxide in excess sodium hydroxide solution Precipitation with sodium hydroxide Copper(II) ions form Precipitation with sodium hydroxide blue precipitates Precipitation with sodium hydroxide Iron (II) ions form Precipitation with sodium hydroxide green precipitates Precipitation with sodium hydroxide iron(III) ions form Precipitation with sodium hydroxide Brown precipitates Halide ions in solution produce precipitates with silver nitrate solution in the presence of dilute nitric acid Silver chloride is Halide ions in solution produce precipitates with silver nitrate solution in the presence of dilute nitric acid White precipitate Halide ions in solution produce precipitates with silver nitrate solution in the presence of dilute nitric acid Silver bromide is Halide ions in solution produce precipitates with silver nitrate solution in the presence of dilute nitric acid Cream precipitate Halide ions in solution produce precipitates with silver nitrate solution in the presence of dilute nitric acid Silver iodide is Halide ions in solution produce precipitates with silver nitrate solution in the presence of dilute nitric acid Yellow precipitate Test for sulfate ions Sulfate ions in solution produce a Test for sulfate ions white precipitate with barium chloride solution in the presence of dilute hydrochloric acid Test for ammonium ions Ammonium ions react with sodium hydroxide solution to form ammonia. Test for ammonium ions Ammonia gas turns Damp red litmus paper blue. Test for nitrate ions Nitrate ions are reduced by aluminium powder in the presence of sodium hydroxide solution to Test for nitrate ions form ammonia Organic compounds Organic compounds burn or char when 04/05/2017 Click here and return to the “Big Picture!”