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HN ADVANCED CHEMISTRY II

HN ADVANCED CHEMISTRY II. CHAPTER 6: THERMOCHEMISTRY - the relationship b/n chemistry and energy - energy – the capacity to do work or to produce heat - law of conservation of energy – energy can be converted from one form to another but can be neither created nor destroyed

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HN ADVANCED CHEMISTRY II

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  1. HN ADVANCED CHEMISTRY II • CHAPTER 6: THERMOCHEMISTRY • - the relationship b/n chemistry and energy • - energy – the capacity to do work or to produce heat • - law of conservation of energy – energy can be converted from one form to another but can be neither created nor destroyed • *energy is either potential (stored) or kinetic (motion) • *some heat is produce during KE • - temp – measure of avg KE of the subs • - heat – transfer of energy b/n 2 objects due to temp diff • *energy can be transferred through work also • - state function or state property – a property that depends on its present state • *a change in this is dependent in the pathway taken • *energy is a state function • - Chemical energy • - system – the part of the universe on which we wish to focus • - surroundings – everything else in the universe

  2. - exothermic – energy flows out of the system • - endothermic – energy flows into the system • * energy gained by the surroundings = energy lost by the system • *exothermic rxns – some PE in bonds is converted into TE • *more energy is released when bonds of products are formed than when bonds are broken in reactants • *endothermic rxns – reverse is true • -The 1st Law of Thermodynamics – energy of universe is constant • - Internal energy (E) = KE + PE q = heat ΔE = q + w w = work • - thermo quantities  # and sign # = magnitude sign = direction from system • *work on surroundings = (-) • *work on system = (+) • Pg233 Sample exercise 6.1

  3. - Gaseous work – • - work done by a gas = expansion • - work done on a gas = compression • w = P x A x Δh P = pressure A = area of piston • Δh = distance piston moved • ΔV = A x Δh  w = -PΔV • *gives size of work required to expand a gas ΔV against P expanding = -w compression = +w • Pg234 Sample exercise 6.2, 6.3 • - Enthalpy and Calorimetry – • - enthalpy – (H) H = enthalpy E = internal energy • H = E + PV P = pressure V = volume • *state function • *at constant P, ΔH equals energy flow • ΔH = qp ΔH = change in enthalpy (also called heat of rxn) • qp = heat at constant pressure

  4. + ΔH = heat absorbed by system, endothermic • - ΔH = heat released to surroundings, exothermic • Pg236 Sample exercise 6.4 • Calorimetry – the science of measuring heat – temp change when a body absorbs or discharges energy as heat - heat capacity= C • C = heat absorbed • increase in T • - specific heat capacity – heat capacity per gram of subs.  J/oC•g or J/K•g • - molar heat capacity – heat capacity per mole or subs.  J/oC•mol or J/K•mol • Energy released = specific heat capacity x mass x change in temp (Tf-Ti) • ΔH = c x m x ΔT • ΔH is an extensive property (depends on amt of sub) – intensive property (does NOT depend on amt of sub) • Pg239 Sample exercise 6.5 (constant pressure)

  5. - when volume is held constant no work is done – use a “bomb” calorimeter • ΔE = q + w = q = qv (constant vol.) • ΔE = CcalorimeterΔT ΔE = (-) exothermic ΔE = (+) endothermic • Pg242 Sample exercise 6.6 • Hess’s Law – in going from reactants to products, ΔH is the same whether the rxn takes one step or a series of steps • ΔHtotal = ΔHstep1 + ΔHstep2 + ΔHstepetc. • *1) If rxn is reversed, sign of ΔH is reversed • 2) Magnitude of ΔH is directly proportional to quantities of reactants and products – if coefficients are multiplied by an integer so is ΔH. • Pg244 Sample exercise 6.7 • Pg245 Sample exercise 6.8

  6. Std Enthalpies of formation (ΔHof) – change in enthalpy that accompanies the formation of 1 mole of a cmpd from its elements w/all subs in their std states • ”o” indicates process has been carried out under std conditions • always written so 1 mole of product is formed  unit = kJ/mol ΔHorxn = ΣnpΔHof(products) - ΣnrΔHof(reactants) Σ = sum of np = mole of products nr = mole of reactants • * value for elements is 0 b/c there is no change in form • Pg249 Sample exercise 6.9 • Pg251Sample exercise 6.10 • Pg252 Sample exercise 6.11

  7. CHAPTER 7: ATOMIC STRUCTURE AND PERIODICITY • A new theory called quantum mechanics • - accounts for behavior of light and atoms • Electromagnetic radiation – • - light energy that travels in waves • - 3 primary characteristics: • 1) wavelength – (λ) – distance b/n 2 consecutive peaks or troughs in a wave • 2) frequency – (ν) - # of waves per second that pass a given point in space • 3) Speed – (c) – speed of light – 2.9979 x 108 m/s • c = λν c = speed of light • λ = wavelength (m or nm) • ν = frequency (cycles/sec) or Hertz  1/s or s-1 • *Classification of EM energy pg276 Figure 7.2 • pg277 Sample exercise 7.1

  8. - Max Planck • - said that matter can gain or lose energy in whole # multiples of “hν” • h = Planck’s constant = 6.626 x 10-34 J•s • ΔE = hν ΔE = change in energy h = Planck’s constant ν = frequency • - showed that energy can only be transferred (quantized) in discrete units of “hν”  called a quantum • pg 293 Sample exercise 7.2 • - Einstein - said that energy can be viewed as a stream of particles photons • Ephoton = hν = hc λ • - derived from famous equation: • E = mc2 from Theory of Relativity • *shows that energy has mass

  9. - can be combined to give mass of a photon of light • m = E = hc/λ = h c2c2 λc • *established dual nature of light – light acts as a particle and a wave • - de Broglie • - showed that particles also act like waves • λ = h h = Planck’s constant mν m = mass ν = velocity λ = wavelength • pg281 Sample exercise 7.3 • - λ caused by space b/n crystals • - waves have properties of particles and particles have properties of waves • - increase size = more particle properties • - decrease size = more wave properties

  10. Atomic spectrum – • - atoms emit excess energy in the form of light emission spectrum • - continuous spectrum – contains all λ of visible light (from white light) • - line spectrum – lines that correspond to discrete λ are produced (when an emission spectrum is passed through a prism) • * only certain energies are allowed for the electron in the hydrogen atom quantized • The Bohr Model • - Niels Bohr developed the Quantum Model for hydrogen • - e- in hydrogen moves around the nucleus on in certain allowed circular orbits • - energy levels available to the e- in the hydrogen atom

  11. - can be used to determine the energy change when an e- changes levels • *ground state – e- in its lowest possible energy state • ΔE = Efinal state – Einitial state • -ΔE = energy lost  more stable atom photon produced • **Bohr’s model was WRONG!! • - didn’t work for other elements - orbits not circular • The Quantum Mechanical Model of the Atom – • - Schrödinger and deBroglie compared the e- to a standing wave • - standing wave – waves are stationary (as in a guitar string) • - they do not travel along the length of the string - wavelengths must be whole #’s

  12. Heisenberg • - concluded that there is a fundamental limitation to just how precisely we can know both the position and momentum of a particle at a given time • Heisenberg Uncertainty Principle – • * the more we know about a particles position the less we know about its momentum and vice versa • - in the Quantum Mechanical Model of the Atom – specific motions are unknown so use probabilities • - size of a hydrogen 1s orbital is the radius that encompasses 90% of total probability • - orbitals are separated by areas of 0 probability of finding an e-nodes – increase n, increase # of nodes • n = 1, only ‘s’ orbitals s – 1 orbital • n = 2, ‘s’ and ‘p’ orbitals p – 3 orbitals • n = 3, ‘s’, ‘p’, and ‘d’ orbitals d – 5 orbitals • n = 4, ‘s’, ‘p’, ‘d’ and ‘f’ orbitals f – 7 orbitals ‘d’ and ‘f’ have different shapes

  13.   - the Bohr model had circular orbits so an e- was always a specific distance from the nucleus - orbital w/same values of n have same energy  degenerate • - Pauli Exclusion Principle – • - e- spin - +½ or -½ - stated that an orbital can hold only 2 e- and they must have opposite spins • - Polyelectronic Atoms – • - atoms w/more than 1 e- • - must consider the following: • 1) KE of e- moving around the nucleus • 2) PE of attraction b/n nucleus and e- • 3) PE of repulsion b/n 2 e-‘s

  14. - b/c we can’t give exact location of e- we can’t calculate the repulsion energy • *e- correlation problem • *use approximations to overcome • - e- in outer energy levels are not as strongly attracted to the nucleus b/c they experience the repulsion of all e- b/n it and the nucleus shielding effect • - orbitals in hydrogen were degenerate – not so in polyelectronic atoms • – prefer to go in order s  p  d  f • The Aufbau Principle • - as p+ are added 1 by 1 to the nucleus to build up the elements, e- are added to the orbitals- represents e- by using orbital diagrams • Ex: 1s 2s 2p *arrows represent e-: arrows represent opposite spins •   H ____ ____ ____ ____ ____ • He ____ ____ ____ ____ ____ • Li ____ ____ ____ ____ ____ • Be ____ ____ ____ ____ ____ • B ____ ____ ____ ____ ____ • Hund’s Rule • - orbitals of the same energy level (degenerate) will each contain an e- b/f any pair up • Ex: C 1s22s22p2 1s 2s 2p ___ ___ ____ ____ ____

  15. e- configurations – give locations of e- • Aufbau diagrams – show spin and which orbitals are filled • Noble gas configurations – allows us to skip writing the inner e- • valence e- - e- in the outermost principal quantum level of an atom – involved in bonding • core e- - inner e- • *elements in the same group have the same # of valence e- and same e- config of valence e- • transition elements – first to have e- in d orbitals • lanthanide and actinide series – Rare Earth Elements - includes ‘f’ orbitals • Representative elements – groups 1A-8A (excludes the transition elements) – group # gives total number of valence e- • pg308Sample Exercise 7.7

  16. Periodic Trends • 1) ionization energy – energy required to remove an e- from a gaseous atom or ion • - 1st ionization energy – energy required to remove the highest energy e- (I1) – as each e-is removed it b/c harder due to the proximity to nucleus and (+) charge atom takes on - IE decreases down a group and increases across a period – there are some exceptions to this general trend • pg311 Sample exercise 7.8 • Sample exercise 7.9 • 2) electron affinity – energy change associated w/the addition of an e- to a gaseous atom - EA decreases down a group and increases across a period – if an unstable ion forms there is a decrease in EA • 3) atomic radius – the size of an atom – can be measured distance b/n atoms in a molecule (½ the distance) in diatomics covalent atomic radii – other nonmetallic radiicome from measures taken from cmpds formed – metallic radii – from measures b/n metals atoms in metal crystals *for rep elements increase down a group b/c addition of energy levels and decrease across a period due to the increase in nuclear charge so e- are pulled closer • pg313 Sample exercise 7.10

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