Chem Highlights of last lecture. What makes an explosive? What makes an explosive? A/Prof Sébastien Perrier. Interregnum: Nitrogen Chemistry

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1 Chem 1101 A/Prof Sébastien Perrier Room: 351 Phone: Unless otherwise stated, all images in this file have been reproduced from: Blackman, Bottle, Schmid, Mocerino and Wille, Chemistry, 2007 (John Wiley) ISB: Slide 25-1 Prof Scott Kable Room: 311 Phone: s.kable@chem.usyd.edu.au A/Prof Adam Bridgeman Room: 222 Phone: a.bridgeman@chem.usyd.edu.au Slide 25-2 ighlights of last lecture Interregnum: itrogen Chemistry CCEPTS Entropy 2 nd Law and spontaneity Standard Entropy Gibbs Free Energy and spontaneity CALCULATIS Entropy of reaction DG = D - TDS Purpose: Earlier concepts: Themes: To reinforce several earlier concepts in one application: itrogen Chemistry Shapes (Lewis structures), Thermochemistry, xidation numbers, Bonding itrogen fuels and explosives itrogen in the atmosphere Slide 25-3 Slide 25-4 What makes an explosive? What makes an explosive? Texas City docks, Galveston 16 th April, 1947 Slide 25-5 Slide

2 What makes an explosive? What makes an explosive? What is the chemical requirement of a high explosive? Most high explosives contain nitrogen. Why? Why are compounds sometimes explosive, and sometimes fuels, or even safer? Building demolition, Boston Slide 25-7 C (nitroglycerine) ΝΗ 4 ΝΟ 3 ammonium nitrate C 3 trinitrotoluene (TT) Slide 25-8 What makes an explosive? (1) What is the chemical requirement of a high explosive? AS: The reaction must produce a large amount of energy (exothermic), released in the form of a pressure wave (i.e. PV-type work is done entropically favoured) nitroglycerine C (l ) > (g) + 3C 2 (g) (g) (g) 7.25 moles of gas produced for each mole of nitroglycerine trinitrotoluene (TT) C (s) > 6 C(g) (g) (g) + C(s) 10 moles of gas produced for each mole of TT PLUS! The reaction is very exothermic, therefore the What makes an explosive? (2) Reaction energy diagram transition state Reaction Coordinate gases are hot and expand even more rapidly. Slide 25-9 Slide energy E a reactant product C > C Transition States BrC Br - + C 3 Br C + - > Br C - > Br - + C TRASITI STATE or ACTIVATED CMPLEX geometry through which system must pass between reactant and product > higher energy than reactants or products not a stable molecule! Slide

3 Transition States More on Transition States Energy E a (fwd) E a (rev) BrC rxn Br - + C 3 Forward reaction is EXTERMIC, Reverse reaction is EDTERMIC Slide Activation energies affect the rate at which reactions occur (Kinetics - see later). Large activation energies lead to slow reactions since only a small fraction of reagents have enough energy to overcome the activation energy barrier to convert into products. Small activation energies generally lead to fast reactions since a large fraction of reagents have enough energy to overcome the activation energy barrier. Single component reagents with low E a and large negative Explosives. Slide What makes an explosive? (3) Why are compounds sometimes explosive, and sometimes useful fuels? int: Where is the oxidant? Fuel or explosive? Why are some compounds great fuels, whereas others are explosive? It is built into the compound! o 2 needed. int: Where is the oxidant? 2 (g) + ½ 2 (g) 2 (g) nitroglycerine C (l ) (g) + 3C 2 (g) (g) (g) Slide Slide Combustion of 2 indenburg Disaster Slide Slide

4 What makes an explosive? (4) Most high explosives contain nitrogen. Why? C 3 trinitrotoluene (TT) C (s) > 6 C(g) (g) (g) + C(s) 2 is a gas (PV work) 2 is extraordinarily stable (exothermic) Slide An entropy bomb? C (s) > 3 (C 3 ) 2 C (g) + 3 (g) triacetone triperoxide (TATP) acetone ozone 3 + aka Mother of Satan used in the 2005 London bombings D ~ 0 DS >> 0 Slide Properties of -compounds Properties of -compounds IGLY VARIED! C 3 Incredibly stable: 2 Extremely explosive: Strong acid 3 Weak base 3 Photochemical smog: 2 Biologically important: + amino acids trinitrotoluene (TT) nitroglycerine Slide Why such a wide range of properties? A: has an intermediate electronegativity and has an odd number of valence electrons. has one of the widest ranges of common oxidation states of any element. Slide Revision: xidation numbers The.. of an atom in its elemental form is ; 0 The.. of an ion is ; its charge The.. of F is always ; -1 The.. of Group 1 elements is always ; +1 The.. of Group 2 elements is always ; +2 The.. of is usually, -2 except in peroxides where it is ; -1 The.. of halogens is usually ; -1 The.. of is +1 with non-metals and -1 with metals. Slide xidation umber Questions What is the oxidation number of Cr in the following? Cr 3 +6 Cr [Cr 2 7 ] 2 +6 Why is the oxidation number important? aming compounds, properties of the compound, identifying redox reactions. Slide

5 xidation states of compounds V IV III II I 0 3 / 3-2, / itric acid itrogen dioxide / Dinitrogen tetroxide itrous acid itrogen oxide itrous oxide Dinitrogen Strong acid Smog Weak acid / weak base Smog + biology Greenhouse gas + laughing gas Stable Elemental ydrides alides xides Most texts have reasonable sections on this. -I -II ydroxylamine ydrazine ybrid amonia/water; explosive ydrazine, rocket fuel xoacids -III 3 / 4 + Amonia Weak base / weak acid Slide Slide Revision: elemental nitrogen Standard State: 2 (g) : 1s 2 2s 2 2p 3 = [e] 2s 2 2p 3 (5 valence electrons) D atom = bond enthalpy = 945 kj/mol (very strong) M structure o p anti-bonding electrons ydrides of Two main hydrides: Ammonia, 3 xidation state of = -3 Figure 5.9 Blackman essential in the nitrogen cycle for life (see later) Complete set of p bonding electrons M bond order = 3 ydrazine, 2 4 xidation state of = -2 rocket fuel Slide Slide alides of xides of nitrogen alides of formula X 3 - molecular compounds; - trigonal pyramidal structure itrous oxide F 3 : colourless gas, fluorinating agent Cl 3 : explosive liquid, industrial use as bleach Br 3 : unstable I 3 : only stable in presence of water itric oxide itrogen dioxide All present in atmosphere, See next lecture 2I 3 (s) > 2 (g) + 3I 2 (g) Fuel and oxidant are pre-mixed again I is the oxidant, is the fuel (reductant) Slide itrate radical Slide

6 xoacids of Summary 3 ; nitric acid Strong acid and strong oxidiser; colourless liquid; in nitrate ion all - bonds are equal, B..~1.3; nitrate salts are mostly soluble. 2 ; nitrous acid Weak acid, pk a = 3.37 nitrite salts are generally soluble CCEPTS -compounds Explosive vs controlled reactions Basic info about hydrides, halides, oxides, etc CALCULATIS Thermochemical calculations involving explosives and fuels. Slide Slide