Chem 1211 1st Edition Exam 3 Study Guide Lectures 14 21 Chapter 5 3 5 8 Explain heat of fusion and heat of vaporization Heat of fusion is the energy that is required to convert a substance from a solid at its melting point to a liquid heat of vaporization is the energy transferred as heat to convert a liquid at its boiling point to a vapor The total energy transferred as heat is the sum of the energies of the individual steps Qtotal q1 q2 q3 For example to convert 500 grams of ice at 50 degrees C to water vapor at 200 degrees celcius 1 2 3 4 5 Warm ice to 0 degrees celcius Converti to liquid water at 0 degrees celcius Warm liquid water to 100 degrees celcius Evaporate at 100 degrees celcius Warm the water vapor to 200 degrees celcius Then add all of the q s together First law of Thermodynamics U q w Aka change in energy content energy transferred as heat to from system energy transferred as work to from the system SIGN IS VERY IMPORTANT o For an endothermic reaction q is positive for an exothermic reaction q is negative o When work is done on the system w is positive when work is done by the system w is negative W P x V o Work at constant pressure pressure x change in volume State function changes in quantities depend only on the initial and final state ex enthalpy temperature volume energy o You can determine enthalpy change using two other reactions o Example What is the enthalpy change for the first reaction 2 C s O2 g 2 CO g delta Hrxn 2 CO g O2 g 2 CO2 g delta Hrxn 566kJ C s O2 g CO2 g delta Hrxn 393kJ ANSWER 221 kJ Reasoning o Double everything in the third equation gives you 786 kJ o Delta H1 Delta H2 Delta H3 o 566 786 o 220 Hess s Law if a reaction is the sum of two or more other reactions the enthalpy change rH for the overall process is the sum of the rH values of those reactions o Example Calculate the enthalpy change for the reaction in which 30 0 g of aluminum reacts with oxygen to form Al2O3 at 25 degrees Celsius and one atmosphere o 4 Al s 3 O g 2 Al2O3 s delta Hf Al2O3 1676 kJ mol ANSWER Use stoichiometry Convert 30 grams of Al to 1 11 moles Al It takes two moles of Al to get one mole of Al2O3 according to the equation so divide 1 11 by 2 to get 555 moles Al 2O3 Multiply 555 by 1676 kJ moles to get your answer approx 930 2 kJ rH n fH products n fH reactants o To find the enthalpy change add up the molar enthalpies of formation of the products each multiplied by its stoichiometric coefficient n and subtract from this the sum of the molar enthalpies of formation of the reactants each multiplied by its stoichiometric coefficient Product favored reaction at equilibrium reactions in which reactants are largely converted to products when equilibrium is reached Reactant favored reaction at equilibrium reactions in which only small amounts of product are present at equilibrium In most cases reactions with a positive enthalpy change are reactant favored and reactions with a negative enthalpy are product favored Chapter 6 Wavelength distance between successive crests high points of a wave measured in meters or nanometers Frequency the number of waves that pass a given point in some unit of time usually per second the frequency that stands for 1 wave per second is a hertz Wavelength and frequency are inverses o As wavelength goes down frequency goes up Red has the greatest wavelength so it has the lowest frequency Follow ROY G BIV C speed of light 3 x 108 mps w wavelength in meters x f frequency in Hertz E energy h Planck s constant x f o H 6 626 x 10 34 Js o Example What is the energy of 122 m radiation from a microwave oven Answer 1 63 x 10 24 J Reasoning To find the energy use the equation e hf but first you need to find the frequency You know the wavelength 122m so plug it into the equation c wf to get a frequency of 2 45x109 Hz Then multiply that frequency times Planck s constant to get the energy o Cosmic rays x rays UV visible infrared microwave radiowave energy and frequency wavelength increase this way increases this way total energy of an electron in the nth level Rhc n2 R Rydberg constant 1 0974 x 107 m 1 P Planck s constant c speed of light n principle quantum number Rydberg Equation 1 wavelength R 1 n12 1 n22 n1 n2 the quantum number n defines the energies of the allowed orbits in the H atoms the electron gap decreases as n increases deBroglie wavelength w h mv m mass v velocity paramagnetic elements and compounds that have unpaired electrons are attracted to a magnet diamagnetic substances in which all electrons are paired and experience a repulsion from a magnetic field Chapter 7 Quantum numbers a n periodic row or shell b l shape s p d f g h c m l l d spin number 1 2 or 1 2 Aufbau Principle a Rule 1 fill starting with lowest order of n l b Rule 2 if n l is the same start with lower n Example Which two orbitals have the same value for n l i 2s 2p ii 2s 3s iii 2p 3p iv 2p 3s 1 ANSWER iv for 2p add 2 1 and for 3s add 3 0 In the periodic table Rows 1A and 2A are s orbitals start with 1 Rows 3A and 8A are p orbitals start with 2 B rows are d orbitals start with 3 Example What is the electron configuration for chlorine I 1s22s22p5 He 2s22p5 3s23p5 Ne 3s23p5 Ne 3s13p6 1 ANSWER Ne 3s23p5 2 Reasoning noble gases are completely filled He 1s2 Ne 1s22s22p6 Chlorine is all of Neon plus 3s2 and 3p5 cations have a positive charge so they have fewer electrons anions have a negative charge so they have more electrons cations shrink and anions expand i charge smaller than corresponding atom ii charge larger than their corresponding atom II III IV V Trends Atomic radius increases as you move from the top to the bottom of the periodic table Atomic radius decreases as you move left to right across the periodic table Atomic energy is has the opposite trends Chapter 8 Definition isoelectronic has the same number of electrons Example With what atoms are K and Br isoelectronic i He Ne ii Ne Ar iii Ar Kr iv Kr Xe 1 ANSWER Ar Kr a REASONING Because K is it has one less electron than normal and because Br is it has one more electron than normal Octet rule element seeks to be surrounded by 8 electrons noble gases have 8 electrons and are stable Exceptions hydrogen can only have …