CYL100: Applied Chemistry Lecture Slides PDF

Institute Core Course for B.Tech. Program CYL100: Applied Chemistry Dr. Arup Mukherjee Assistant Professor Department of Chemistry  Overview Credit: 3 (3-0-0) Electrochemical Systems: Electrochemical cells and EMF,...

Institute Core Course for B.Tech. Program CYL100: Applied Chemistry Dr. Arup Mukherjee Assistant Professor Department of Chemistry  Overview Credit: 3 (3-0-0) Electrochemical Systems: Electrochemical cells and EMF, Applications of EMF measurements, Nernst Equation, Batteries, Fuel cell, corrosion and its control; Kinetics of Chemical Reactions and catalysis: Reversible, consecutive and parallel reactions, Steady state approximation, and Chain reactions. Physical adsorption, chemisorption, Freundlich’s expression, Langmuir adsorption isotherm, and heterogeneous catalysis; Bonding Models in inorganic Chemistry: Molecular orbital theory, Valence bond theory, LCAO, and Crystal field theory; Coordination Chemistry: Coordination numbers, Chelate effect, 2  Overview …….Coordination complexes and application, Bio-inorganic Chemistry: Metal ions in Biological systems, environmental aspects of Metals, Organometallic chemistry, 18 electron rules, Industrially relevant chemical reactions and mechanism, Metallic-lithium, sodium and its compounds and their energy storage applications; Engineering materials and Polymer Chemistry: Glass, composites, magnetic materials, Polymer, Properties, Polymer processing, Industrial polymers, conducting polymers; Natural Products and Biomolecules: Amino acids/nucleic acids/proteins/lipids, Enzymes, Vitamins, Biomacromolecules, and Solid phase synthesis; Fuels and Combustion: Properties of fuels, Calorific value, Petroleum and petrochemicals, biofuels. 3  An Overview Textbooks/ Reference Books: 4  Evolution Methodology The tentative proposal is the following which is subject to be change as per the situation. COMPONENT MARKS Exam (Number of Exam) 50 (Mid-Sem Exam) Assignment 10 (?) Quiz 20 (1 Quiz) Total 70 or 80 5 Periodic Table 6  General Feeling About Main Group Chemistry Very boring… Lot of equations to mug up… No color, no magnetism - No high spin low spin; no CFT. Textbooks are huge in size and have too much information. How do we know which equation is important? This is something about boron and sulfuric acid etc.: boring stuff. What is the use? No use of this chemistry in catalysis, in organic chemistry, or bioinorganic chemistry? 7 Transition Metal Chemistry Versus Main Group Chemistry and Rural Environment 8 Top 20 Industrial Chemicals Produced in US, 2010 9 The P-Block Elements 10 The Trans Effect Landmark Discoveries in the Chemistry of Main Group Elements 11 940 AD 12  Antoine-Germain Labarraque (1777-1850) Chlorinated lime and Chlorine water 13 1847 14  para-Chloro-meta-xylenol It may be used mixed with water or alcohol. Chloroxylenol is most effective against Gram-positive bacteria. It works by disruption of the cell wall and stopping the function of enzymes. 15 1669 16 1812 17 1886 18 1904 19 1913 20 1938 21 22 1954 23 1967 24 2010 25  Hypervalency of Main Group Compounds  Hypervalency The ability of an atom in a molecular entity to expand its valence shell beyond the limits of the Lewis octet rule. Hypervalent compounds are common for the second and subsequent row elements in groups 15-18 of the periodic table. A description of the hypervalent bonding implies a transfer of the electrons from the central (hypervalent) atom to the nonbonding molecular orbitals which it forms with (usually more electronegative) ligands. A typical example of the hypervalent bond is a linear three-centre, four-electron bond, e.g. that of F–P–F fragment of PF5. 26 Hypervalency 27  The N-X-L Designation (Hypervalency) The N-X-L designation is used to describe hypervalent molecules, where N is ) the number of formally assignable valence electron to the central atom, X is the symbol of the central atom and L is the number of ligands/substituents directly bonded to the central atom. The compounds can have coordination numbers from two to six. All the known compounds of rare gases as central atom come under the category of hypervalent molecules. Most of the hypervalent compounds have their structure derived from a trigonal bipyramid or octahedral geometry. 28 Hypervalency 29 Hypervalency 30 Synthesis of Hypervalent Compounds ) 31  Explanation of Hypervalency Pauling’s Expanded Octet Model 32  Explanation of Hypervalency Through the promotion of electrons into vacant high-lying d-orbitals leading to sp3d/sp3d2 hybridizations. It has been shown by many theoretical researchers that even if d orbitals are necessary to provide quantitative bond energies in hypervalent species, these orbitals have occupancies of only 0.3 electrons at the most. 33  Three Centre Four Electron (3c-4e) Model Proposed in 1951 by Pimental and Rundle In a 3 centre 4 electron molecular system, three atoms or fragments each contribute a single atomic orbital from which one can construct a set of three molecular orbitals (MO’s) of bonding, non-bonding, and antibonding character. 34  Three Centre 4 Electron (3c-4e) Model ▪ Hypervalent bonding is most simply illustrated for [FHF]− anion, where H has four valence electrons, exceeding its normal maximum of 2e. ▪ The resulting 3 center–4 electron (3c–4e) bonding leads to half-order bonding between H and each F. ▪ This results in somewhat longer bonds (1.15 Å) than in the corresponding non-hypervalent species, HF (0.92 Å). 35 Hypervalent SF6 Molecule The ligand group orbitals thus obtained for the F6 part of SF6 are a1g, t1u and eg. The qualitative molecular orbital diagram of SF6 can be constructed by matching the symmetry of the S valence orbitals and the LGOs of the F6 fragment. While orbital overlap occurs for the a1g and t1u orbitals, the eg set remains non-bonding. Since the eg orbitals are nonbonding, there are only 4 bonding pairs of electrons and therefore the bond order for SF6 is 2/3. 36 Increased Reactivity of Hypervalent Species 37 Isolation of Hypervalent Species 38 Important Compounds and Concepts Related to the Main Group Chemistry  Kinetic Isotope Effect ▪ A kinetic isotope effect (KIE) is the change in the reaction rate of a chemical reaction when one of the atoms in the reactants is replaced by one of its isotopes. ▪ Formally, it is the ratio of rate constants for the reactions involving the light (kL) and the heavy (kH) isotopically substituted reactants. KIE = kL/kH 39  Kinetic Isotope Effect Nitration of Benzene: Iodination of Phenol: 40 Hydrogen Economy 41 Types of Hydrogen 42 Emission of Different Hydrogens Green hydrogen: 0 kgCO2 /kg H2. Blue hydrogen: 3.5-4 kgCO2 /kg H2. Grey hydrogen: 10 kgCO2 /kg H2. 43 Plant of a Green Hydrogen 44 Green Hydrogen Production 9 45  Electrolysis of Water In the year 1789, Jan Rudolph Deiman and Adriaan Paets van Troostwijk first demonstrated water electrolysis using an electrostatic generator. In the mid-1960s, GE (General Electric) developed the proton exchange membrane for producing electricity for their Gemini space program. 46 Electrolysis of Water For water electrolysis, the energy is required as electrical energy from a DC power source. At room temperature, the splitting of water is very small approximately 10-7 moles/liter. Water is a very poor conductor of electricity. 47  Electrolysis of Water Water electrolysis technology can be broadly divided into three categories based on the electrolytes employed during the electrolysis procedure. 48 Alkaline Electrolysis The concentration of the electrolyte solution is usually up to 40 wt% to provide maximum electrical conductivity 49 Electrolysis of Water 50 Electrolysis of Water 51 Polymer/Proton Electrolyte Membrane Electrolysis 52 Electrolysis of Water 53  Electrolysis of Water Advantages: High purity of hydrogen gas Low power consumption Ecological cleanness High safety, easy handling, and maintenance Disadvantages: The cost of the components is high Comparatively low durable Chance of the swelling of the polymer membrane 54 Steam/Solid Oxide Electrolysis 55 Electrolysis of Water 56  Electrolysis of Water Advantages: It is having high-pressure operations High efficiency (almost 100 percent) We can get high temperatures from solar energy, which is a renewable source. Disadvantages: Still this technology is laboratory phase Low durability due to high heat The design of the system is quite bulky. 57  Electrode Materials for Electrolysis of Water High cyclability High ionic conductivity High surface area High mechanical, thermal, and chemical stability 53 Electrolysis of Water 54 Fuel Cell 55 Hydrogen Fuel Cell Bus  Hydrogen Storage Material Hydrogen has the highest energy density by weight and is considered to be potentially the cleanest of fuels, emerging only water as an oxidation product. In spite of this, storage of large amounts of hydrogen in a lightweight tank for use in automobiles has presented a major challenge to its widespread use. Transportation of compressed hydrogen requires a very high-pressure technology and is a concern of public acceptance. Moreover, for liquid hydrogen, the requirement of harsh cryogenic 56 conditions presents significant disadvantages. Liquid Organic Hydrogen Carrier (LOHC) LOHCs are low molecular weight organic compounds in the liquid state at room temperature that can liberate hydrogen gas (fuel) in the presence of a catalyst, forming spent fuel that can be converted back to the charged fuel by hydrogenation, thus closing the loop. 57  Liquid Organic Hydrogen Carrier (LOHC) Methylcyclohexane/toluene (6.1 wt% theoretical hydrogen storage capacity) 58  Liquid Organic Hydrogen Carrier (LOHC) The hydrogen storage capacity of decalin (DEC) is 7.3 wt%. 59 Prototype Truck Powered by H2 from LOHC 60 Methanol Economy 61  Methanol Economy CO2 hydrogenation to methanol is an exothermic reaction (CO2 + 3H2 → CH3OH + H2O, ΔH298 K = −49.4 kJ mol–1); therefore, a high reaction temperature is thermodynamically unfavorable. The development of catalysts that enable low-temperature operation has thus been vigorously pursued. 62  Benefits of Methanol Lower Production Costs Handling and Transportation Lower Flammability Risk High Octane and Horsepower Environmental Benefits Reduces Oil Import Bill “Methanol Economy will also create close to 5 million jobs through methanol production/application and distribution services. Additionally, Rs 6000 crore can be saved annually by blending 20% DME (Di-methyl Ether, a derivative of methanol) in LPG. This will help the consumer in saving between Rs 50-100 per cylinder” 63 Binding of H2 with Metal: Key Step During Hydrogenation Splitting ▪ Initially, the filled σ orbital of H2 donates a pair of electrons to the vacant d orbital of the metal: two-electron, three center (2e,3c) bond for this interaction. ▪ Back bonding into the H–H σ* causes additional weakening or even breaking of the H–H σ bond because the σ* is antibonding with respect to H–H. ▪ Free H2 has an H–H distance of 0.74 Å, but the H–H distances in H2 complexes go all the way from 0.82 to 1.5 Å. ▪ Eventually, the H–H bond breaks and a dihydride is formed. 64  Metal Hydride Batteries ▪ A nickel-metal-hydride battery is a type of rechargeable battery similar to the widely used nickel-cadmium (NiCd) battery. ▪ The main advantages of the metal hydride over the NiCd batteries are that they are more easily recycled and do not contain the very toxic element Cd. ▪ The attractive properties of nickel-metal-hydride batteries include high power, long life, a wide range of operating temperatures, short recharging times, and sealed, maintenance-free operation. 65  Metal Hydride Batteries ▪ The cathode is made from a mixed metal alloy at which the metal hydrides are formed reversibly. ▪ The anode is made from nickel hydroxide. The electrolyte is a basic solution of 30 per cent by mass KOH. The electrode reactions are: ▪ There is no net change in the electrolyte concentration over the charge− discharge cycle. ▪ The strength of the M–H bond in the metal hydride is crucial to the operation of the battery. The ideal bond enthalpy falls in the range 25−50 kJ mol−1. 66