Fund. of Chem. for Engineers
Fund. of Chem. for Engineers CHEM 1372
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This 48 page Class Notes was uploaded by Dominic Kling on Saturday September 19, 2015. The Class Notes belongs to CHEM 1372 at University of Houston taught by Shoujun Xu in Fall. Since its upload, it has received 77 views. For similar materials see /class/208149/chem-1372-university-of-houston in Chemistry at University of Houston.
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Date Created: 09/19/15
Subatomic Particles Protons and neutrons are located at the center of an atom at the nucleus Electrons are dispersed around the nucleus For neutral atoms of e39 equals to of p Cations atoms loses that number of e39 Anions atoms gains that number of e39 Table 21 Subatomic Particles Approximate Relative Location Particle Symbol Relative Mass Charge in Atom Proton pJr 1 1 Inside nucleus Neutron n 1 0 Inside nucleus Electron e0 0000545 1 Outside nucleus Copyright 2004 Pearson Prentice Hall Inc General Chemistry 4 h edition Hill Petrucci McCreary Perry Isotopes and Average Mass Atoms that have the same number of protons but different numbers of neutrons are called isotopes The atomic number Z is the number of protons in the nucleus of a given atom of a given element The mass number A is an integral number that is the sum of the numbers of protons and neutrons in an atom The number of neutrons A Z Average mass of an element from two isotopes Ave Mass Isotopel X Abundancel Isotope Mass2 X 100 Abundancel General Chemistry 4 h edition Hill Petrucci McCreary Perry Wavelength Frequency amp Energy The relationship between wavelength and frequency clV c 300 X 108 ms in vacuum speed of light Ehv E energy of one photon h Planck s constane General Chemistry 4 h edition Hill Petrucc i McCreary Perry 4 Bohr s Hydrogen Atom Electron energy E was quantized Each speci ed energy value is called an energy level of the atom Er1 Bn2 n is an integer andB 2179 X 10 18 J n l is ground state 1L AE B112 n2 AEhV General Chemistry 4 h edition Hill Petrucc i McCreary Perry Valence Electrons and Core Electrons The valence shell is the outermost occupied principal shell The valence shell contains the valence electrons For main group elements the number of valence shell electrons is the same as the periodic table group number 2A elements two valence electrons etc The period number is the same as the principal quantum number n of the electrons in the valence shell 0 Electrons in inner shells are called core electrons Pammagnetism atoms or ions with unpaired electrons General Chemistry 4 h edition Hill Petrucci McCreary Perry Quantum Numbers The principal quantum number n 0 Determines the energy of the orbital 0 Can have positive integral values from 1 2 The orbital angular momentum quantum number l 0 Determines the shape of the orbital Can have integral values from 0 l 2 n l s p d f The magnetic quantum number ml 0 Determines the orientation of the orbital 0 Can have any integral values from l to l 21l values The electron spin quantum number ms Explains some ne structures in atomic spectrum 0 Can have values ofl2 and l2 Shape of orbitals s pX py pZ and d General Chemistry 4 h edition Hill Petrucci McCreary Perry Naming Binary Compounds Molecular compounds 0 The name consists of two words 0 First word name of the element that appears rst in the formula 0 Second word stem of the name of the second element ending with l39de Names are further modi ed by adding pre xes to denote the numbers of atoms of each element in the molecule Molecular compounds 0 No pre xes for the number of ions Hydrates of ionic compounds 0 The compound name is followed by hydrate Where the blank is a pre x to indicate the number of water molecules General Chemistry 4 h edition Hill Petrucc i McCreary Perry Naming Binary Compounds and Hyd rates N203 dinitrogen trioxide AlCl3 aluminum chloride FeS ironII sul de CaClzo 6HZO calcium chloride hexahydrate General Chemistry 4 h edition Hill Petrucc i McCreary Perry Monatomic Ions Group IA metals form ions of 1 charge Group IIA metals form ions of 2 charge Aluminum a group IIIA metal forms ions With a 3 charge Nonmetal ions of groups V VI and VII usually have charges of 3 2 and 1 respectively Group B metal ions transition metal ions often have more than one possible charge A Roman numeral is used to indicate the actual charge A few transition elements have only one common ion Ag Zn Cd and a Roman numeral is not often used General Chemistry 4 h edition Hill Petrucci McCreary Perry 10 Writing Lewis Structures Skeletal Structures The skeletal structure shows the arrangement of atoms Hydrogen atoms are terminal atoms bonded to only one other atom The central atom of a structure usually has the lowest electronegativity In oxoacids HClO4 HNO3 etc hydrogen atoms are usually bonded to oxygen atoms Molecules and polyatomic ions usually have compact symmetrical structures General Chemistry 4 h edition Hill Petrucci McCreary Perry VSEPR Notation and Strategy In the VSEPR notation used to describe molecular geometries the central atom in a structure is denoted as A terminal atoms as X and the lone pairs of electrons as E Applying the VSEPR method 1 Draw a Lewis structure of the molecule or ion 2 Determine the number of electron groups 3 Identify the electrongroup geometry 4 Identify the molecular geometry General Chemistry 439h edition Hill Petrucci McCreary Perry 11 ElectronGroup Geometries An electron group is a collection of valence electrons locallzed 1n a region around a central atom One electron group A single unpaired electron an unshared pair of valence electrons a bond single double or triple The repulsions among electron groups lead to an or1entatlon of the groups that 1s called the electron group geometry These geometries are based on the number of electron groups 12 Electron Electrongroup groups geometry 2 Linear Trigonal planar 4 Tetrahedral 5 Trigonal bipyramidal 6 Octahedral General Chemistry 4 h edition Hill Petrucci McCreary Perry Hybridization of Atomic Orbitals Table 102 Hybrid Orbitals and Their Geometric Orientation Hybrid Orbitals Geometric Orientation Example sp Linear BeCl2 Sp2 Trigonal planar BF3 sp3 Tetrahedral CH 4 sp3d Trigonal bipyramidal PC15 sp3 d2 Octahedral SF6 Predicting hybridization count the electron groups Expanded valence shell The total number of orbitals does NOT change during hybridization General Chemistry 4 11 edition Hill Petrucci McCreaIy Perry 14 Formal Charge Formal charge is the difference between the number of valence electrons in a free uncombined atom and the number of electrons assigned to that atom When bonded to other atoms in a Lewis structure When formal charges are required they should be as small as possible Negative formal charges should appear on the most electronegative atoms Adjacent atoms in a structure should not carry formal charges of the same sign General Chemistry 4 h edition Hill Petrucci McCreary Perry 15 Resonance Delocalized Bonding When a molecule or ion can be represented by two or more plausible Lewis structures that differ only in the distribution of electrons the true structure is a composite or hybrid of them The different plausible structures are called resonance structures The actual molecule or ion that is a hybrid of the resonance structures is called a resonance hybrid Electrons that are part of the resonance hybrid are spread out over several atoms and are referred to as being delocalized Copyright 2004 Pearson Prentice Hall Inc General Chemistry 4 h edition Hill Petrucci McCreary Perry Formula Mass Moles Atoms Formula mass sum of the masses of the atoms or ions present in a formula unit Mole mol amount of substance that contains as many elementary entities as there are atoms in exactly 12 g of the carbon 1 2 isotope Ayogadro s number N A 6022 X 1023 mol 1 General Chemistry 4 h edition Hill Petrucc i McCreary Perry 16 Balancing Chemical Equations If an element is present in just one compound on each side of the equation try balancing that element rst Balance any reactants or products that eXist as the free element last 0 In some reactions certain groupings of atoms such as polyatomic ions remain unchanged In such cases treat these groupings as a unit At times an equation can be balanced by first using a fractional coefficients The fraction is then cleared by multiplying each coefficient by a common factor General Chemistry 4 h edition Hill Petrucci McCreary Perry 17 Stoichiometric Equivalence and Reaction Stoichiometry A stoichiometric factor or mole ratio is a conversion factor obtained from the stoichiometric coef cients in a chemical equation In the equation COg 2 H2g gt CH3OH1 1 mol CO is chemically equivalent to 2 mol H2 1 mol CO is chemically equivalent to 1 mol CH3OH 2 mol H2 is chemically equivalent to 1 mol CH3OH 1 mol CO 1 mol CO 2 mol H2 2 mol H2 1 mol CH3OH 1 mol CH3OH General Chemistry 4 h edition Hill Petrucci McCreary Perry 19 Outline of Stoichiometry Involving Mass Grams of substance A 1 I X molar mass of A Molarity x Volume 9 Moles of substance A X 11101 B mol A Moles of substance B 9 Moles Vlolarity Volume gtlt molar mass of B Grams of substance B Copyright 2004 Pearson Prentice Hall Inc General Chemistry 4 h edition Hill Petrucci McCreary Perry 20 Limiting Reactant We recognize limiting reactant problems by the fact that amounts of two or more reactants are given One way to solve them is to perform a normal stoichiometric calculation of the amount of product obtained starting With each reactant The reactant that produces the smallest amount of product is the limiting reactant General Chemistry 4 h edition Hill Petrucc i McCreary Perry Yields of Chemical Reactions The theoretical yield of a chemical reaction is the calculated quantity of product in the reaction The actual yield is the amount you actually get When you carry out the reaction Percent yield actual yield theoretical yield X 100 General Chemistry 4 h edition Hill Petrucci McCreary Perry 21 22 Molarity and Dilution moles of solute Molarity liters of solution Mass Mole 69 Volume M X Vconc Mdil X Vdil COllC General Chemistry 4 h edition Hill Petrucc i McCreary Perry 23 The Rate Law amp Method of Initial Rates d A The method of initial rates is a method of establishing the rate law for a reaction nding the values of the exponents in the rate law and the value of k A series of experiments is performed in which the initial concentration of one reactant is varied Concentrations of the other reactants are held constant General Chemistry 4 h edition Hill Petrucci McCreary Perry Summary of Kinetic Data Table 134 A Summary of Kinetic Data for Reactions of the Type A gt products Integrated StraightLine Units Half Order Rate Law Rate Law Plot k of k life 1 0 Rate k A kt A0 A vs I slope M s E A 0693 1 Rate kA In E kt in A vs 2 slope 3 A10 k 2 Rate kA2 1Avst slope M 1 s 1 AL t A10 Copyright 2005 Pearson Prentice Hall Inc General Chemistry 4 h edition Hill Petrucc i McCreary Perry kA0 25 Catalysis A catalyst increases the reaction rate without itself being used up in a chemical reaction In general a catalyst works by changing the mechanism of a chemical reaction Often the catalyst is consumed in one step of the mechanism but is regenerated in another step The pathway of a catalyzed reaction has a lower activation energy than that of an uncatalyzed reaction so more molecules at a fixed temperature have the necessary activation energy The yield does NOT change General Chemistry 4th edition Hill Petrucci McCreary Perry Chemical Equilibrium When a system reaches equilibrium the forward and reverse reactions continue to occur but at equal rates Equilibrium Forward and reverse rates are equal Reaction rate i n I I I t e Time After equilibrium the concentrations of reactants and products remain constant General Chemistry 4 h edition Hill Petrucc i McCreary Perry 27 The Equilibrium Constant Expression For the general reaction aAbB gtgGhH The equilibrium expression is GgH K A Bb General Chemistry 4 h edition Hill Petrucc i McCreary Perry 28 Equilibria Involving Gases and Kp PGgPHh P AMP 13 Kc and Kp are related by Kp Kc RDAWgaS P Angas mol of gaseous products mol of gaseous reactants gh a b The equilibrium constant expression does not include terms for pure solid and liquid phases Example CaCO3s CaOs COzg Kc C02 Kp PCOZ General Chemistry 4 h edition Hill Petrucc i McCreary Perry 29 The Reaction Quotient Q For nonequilibrium conditions the expression having the same form as Kc or K1 is called the reaction quotient Qc or Qp The reaction quotient is not constant for a reaction but is useful for predicting the direction in Which a net change must occur to establish equilibrium To determine the direction of net change we compare the magnitude of Qc to that of Kc Qc lt Kc forward reaction Qc gt Kc reverse reaction Qc Kc equilibrium General Chemistry 4 h edition Hill Petrucci McCreary Perry 30 Le Chatelier s Principle When any change in concentration temperature pressure or volume is imposed on a system at equilibrium the system responds by attaining a new equilibrium condition that minimizes the impact of the imposed change If the concentration of one of the reactants is increased Q is now less than Kc The concentrations of the products increase the equilibrium is shifted to the right If the concentration of one of the products is increased Q is now greater than Kc The concentrations of the reactants increase the equilibrium is shifted to the left General Chemistry 4 h edition Hill Petrucc i McCreary Perry 31 Changing External Pressure or Volume in Gaseous Equilibria When the external pressure is increased or system volume is reduced an equilibrium shifts in the direction producing the smaller number of moles of gas When the external pressure is decreased or the system volume is increased an equilibrium shifts in the direction producing the larger number of moles of gas If there is no change in the number of moles of gas in a reaction changes in external pressure or system volume have no effect on an equilibrium gt Example H2g 12g 2H1 equilibrium is a affected by pressure changes General Chemistry 4 h edition Hill Petrucci McCreary Perry 32 Temperature Changes and Catalysis Raising the temperature of an equilibrium mixture shifts equilibrium in the direction of the endothermic reaction lowering the temperature shifts equilibrium in the direction of the exothermic reaction Consider heat as though it is a product of an exothermic reaction or as a reactant of an endothermic reaction and apply Le Chatelier s principle Adding a catalyst does not affect an equilibrium state A catalyst merely causes equilibrium to be achieved faster General Chemistry 4 h edition Hill Petrucci McCreary Perry First Law of Thermodynamics Energy cannot be created or destroyed AU U nal Jinitial Sign ConventionA U q W q PAV Energy entering a system carries a positive sign heat absorbed by the system endothermic or work done on the system Energy leaving a system carries a negative sign heat given of by the system exothermic or work done by the system General Chemistry 4 h edition Hill Petrucci McCreary Perry 33 34 Properties of Enthalpy Enthalpy is the sum of the internal energy and the pressure Volume product of a system HUPV AH qP Enthalpy is an extensive property so are U G S It depends on how much of the substance is present General Chemistry 4 h edition Hill Petrucc i McCreary Perry 35 Calorimetry Heat Capacity Specific Heat Heat evolved in a reaction is absorbed by the calorimeter and its contents In a calorimeter we measure the temperature change of water or a solution to determine the heat absorbed or evolved by a reaction The heat capacity C of a system is the quantity of heat required to change the temperature of the system by 1 C C qAT units are J C The Speci c heat or speci c heat capacity s is the heat capacity of one gram of a pure substance or homogeneous mixture s Cm qmAD qsmAT General Chemistry 4 h edition Hill Petrucci McCreary Perry 36 Measuring Enthalpy Changes for Chemical Reactions For a reaction carried out in a calorimeter the heat evolved by a reaction is absorbed by the calorimeter and its contents grxn QCalorimeter mass x speci c heat x AT Qwater qbomb heat capacity x AT gealonmeter Qwater Qbomb Possible parameters to calculate equilinrium temperature C or s General Chemistry 4 h edition Hill Petrucc i McCreary Perry 37 Hess s Law of Constant Heat Summation Hess s Law If an equation can be expressed as the sum of two or more other equations the enthalpy change for the desired equation is the sum of the enthalpy changes of the other equations Key 1 Build the desired reaction from given reactions Key 2 Remember multiplying appropriate coef cients Key 3 Pay attention to the signs General Chemistry 4 h edition Hill Petrucci McCreary Perry 38 Entropy and Entropy Change The greater the number of con gurations of the microscopic particles atoms ions molecules among the energy levels in a particular state of a system the greater is the entropy of the system Entropy generally increases when Solids melt to form liquids Solids or liquids vaporize to form gases Solids or liquids dissolve in a solvent to form nonelectrolyte solutions A chemical reaction produces an increase in the number of molecules of gases A substance is heated General Chemistry 4 edition Hill Petrucci McCreary Perry 39 Third Law of Thermodynamics amp Standard Molar Entropies Third Law of Thermodynamics the entropy of a pure perfect crystal can be taken to be zero at 0 K The standard molar entropy S is the entropy of one mole of a substance in its standard state Since entropy increases With temperature standard molar entropies are positive even for elements Entropy change of chemical reactions AS 21210 S products Zvr S reactants General Chemistry 4 h edition Hill Petrucci McCreary Perry Second Law of Thermodynamics amp Free Energy The Second Law of Thermodynamics establishes that all spontaneous processes increase the entropy of the universe system and surroundings The quantity TASuniV change AG For a process at constant temperature and pressure is called the free energy AG AH TAS General Chemistry 4 h edition Hill Petrucci McCreary Perry 40 41 Free Energy and Free Energy Change If AG lt 0 negative a process is spontaneous If AG gt 0 positive a process is nonspontaneous If AG 0 neither the forward nor the reverse process is favored there is no net change and the process is at equilibrium At equilibrium AG 0 Therefore at the equilibrium temperature the free energy change expression becomes AHTAS and ASAHT General Chemistry 4 h edition Hill Petrucci McCreary Perry Standard Free Energy Change AG The standard free energy change AG of a reaction is the free energy change When reactants and products are in their standard states The standard free energy of formation AGfO is the free energy change for the formation of 1 mol of a substance in its standard state from the elements in their standard states AGo 2v AG oproducts Zvr AG oreactants p f f The 4le0 is zero for pure elements in their standard state such as 02 g Hg 1 etc General Chemistry 4 h edition Hill Petrucci McCreary Perry 43 Relationship of AG to the Equilibrium Constant Keq AGO RT In Keq Keq is NOT Kc or Kp Solid and liquid ignore Gas use partial pressure in atm Ions or solution use molar General Chemistry 4 h edition Hill Petrucc i McCreary Perry 44 Important Electrochemical Terms An electrochemical cell consists of two halfcells With the appropriate connections between electrodes and solutions Oxidation a species loses electrons to another species Oxidation occurs at anode the substance is reducing agent Reduction a species gains electrons from another species Reduction occurs at cathode the chemical is oxidizing agent Two halfcells may be joined by a salt bridge that permits migration of ions Without completely mixing the solutions The anode is the electrode at Which oxidation occurs The cathode is the electrode at Which reduction occurs In a voltaic cell a spontaneous redox reaction occurs and rrent is generated General Chemistry 4 h edition Hill Petrucci McCreary Perry 45 Cell Diagrams and Examples The anode is placed on the left side of the diagram The cathode is placed on the right side A single vertical line represents a boundary between phases such as between an electrode and a solution A double vertical line represents a salt bridge or porous barrier separating two halfcells PtS FezaC1 Fe3aCI C aCI C2g PtS General Chemistry 4 h edition Hill Petrucci McCreary Perry 46 Common Cells and Baterries Dly cell Alkaline cells Primary cells i e nonrechargeable 15 V Anode Zn Cathode Graphite Moist paste of NH4C1 ZnClz and MnOz Graphite rod Alkaline is more expensive last longer and E0611 Whale does not drop as rapidly IT i CM39g Leadacid battery H t 3 Secondary cells i e rechargeable Pb node E A set of cells each has 2 V c Anode Pb Cathode PbOZ i Cell reaction Pbs Pb02s 2 Haq 2 H504quotaq H250 2 PbSO4s 2 11201 COW Charging reverse reaction Electrolyte density increases General Chemistry 4 h edition Hill Petrucci McCreary Perry 47 Protecting Iron from Corrosion The simplest defense against corrosion of iron is to coat it with paint or metal to exclude oxygen from the surface How about Al which is more active than Fe No need to protect aluminum because its oxide acts as its coating An entirely different approach is to protect iron With a more active metal Galvanized iron has been coated With zinc The zinc provides an alternative anode reaction the zinc corrodes protect1ng the non In cathodic protection an iron object to be protected is connected to a chunk of an active metal such as Mg General Chemistry 4 h edition Hill Petrucci McCreary Perry KineticMolecular Theory and 48 The Combined Gas Law KMT Provides a model for gases at the microscopic level Molecules are in rapid random motion Movement of gases through threedimensional space is called translational motion Combined Gas Law PV nRT If no mass loss PlVlT1 P22T2 P pressure V volume 11 moles of gas mol R constant T temperature K The value of R depends on the units of P and V General Chemistry 4 h edition Hill Petrucci McCreary Perry
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