CHM 1045 Spring 2014Study guide- Exam 3Chapter 6Endothermic- heat has to be supplied to the system BY the surroundings (+)Exothermic- any process that gives off heat, transfers heat from system TO the surroundings (-)Enthalpy (∆H)- thermodynamic function of a systemH=U + PVCalorimetry-measurement of heat changesHeat capacity (C) - amount of heat required to raise the temperature of A GIVEN QUANTITY of the substance by one degree Celsius (units of J/°C)Specific heat(s)- amount of heat required to raise the temperature of ONE GRAM of the substance by one degree Celsius (units J/g x °C)Calculations involving heat (q), mass (m) and temperature (t) change:C=msq=ms ∆ t∆ t=tfinal−tintialConstant Volume Calorimeter:-heat of combustion measured by placing a known mass of a compound in the constant-volume calorimeter, which is filled with oxygen at 30 atm of pressure-qrxnDOES NOT =∆ H because under constant- volume-qcal=Ccal∆ t-example 6.6Constant- Pressure Calorimeter:-used to determine the heat changes for noncombustion reactions-qrxn= ∆ H because under constant-pressure-example 6.7 and 6.8Standard enthalpy of reactions:-the enthalpy of a reaction carried out at 1 atm-equation: Σ n ∆ H °f(products)−∑n ∆ H °j(reactants)-example 6.10Hess’s Law and enthalpy of reaction:-for compounds that cannot be synthesized from their elements-breaking down reaction into a series of reactions-example 6.9Chapter 7Planck’s Theory and Classical Physics:-classical physics thought that energy was continuous and any amount could be released, Planck discovered that atoms and molecules emit energy only in certaindiscrete amounts, or quantaWavelength¿)- distance between identical points in successive wavesAmplitude (A)- vertical distance from middle of the wave to peak or troughFrequency (ν)- number of wavelength that pass a given point per second (cycles/sec = Hertz (Hz)= sec−1)Relationship between speed, wavelength and frequency:speed=(wavelength)(frequency )u=λν-u can be replaced with c for speed of light-example 7.1-remember frequency = Hz (cycles/sec = Hertz (Hz)= sec−1)Maxwell’s Theory of electromagnetic radiation:-electromagnetic radiation- emission and transmission of energy in the form of electromagnetic waves -electromagnetic waves- have two components1. electric field2.magnetic field-2 components have the same wavelength and frequency but travel in different planesElectromagnetic spectrum:-gamma rays-shortest wavelength and highest frequency-radio waves- longest wavelength and lowest frequency-Visible light ranges from wavelength of 400 nm(violet) to 700 nm (red)Planck’s equation to determine Energy, frequency, or wavelength of electromagnetic radiation:E=hν¿ ν=cλso …E=hcλ-h being Planck’s constant-example 7.2Photoelectric effect explained by Einstein:-electrons are ejected from the surface of certain metals exposed to light of a threshold frequency (certain min frequency)-the beam of light is made of particles called photons-If the frequency of the photons is such that the hν is = to the binding energyof the electrons, than the light will knock the electrons loose-If it is a light of higher frequency (smaller wavelength correlates with this) is used the electrons knocked loose will acquire kinetic energy-smaller wavelength = higher energy!hν=KE+W (work function)-A higher light intensity has more photons, thus knocks off a higher number of electrons (higher # of electrons emitted)-example 7.3Bohr’s model of the atom:-emission spectra- continuous or line spectra of radiation emitted by substances-line spectra- light emission only at specific wavelengths-Hydrogen atom:-electron is allowed to occupy only certain orbits of specific energies-attribute emission of radiation from energized hydrogen atom to the electron dropping from a higher-energy allowed orbit to a lower one and emitting a quantum of energy-energies that an electron in a hydrogen atom can occupy:En=−RH(1n2) -explanation of line spectrum of hydrogen: radiant energy absorbed by the atom causes the electron to move from a lower-energy state (smaller n value) to a higher energy state (higher n value). Radiant energy is emitted (photon) when the electron moves from a higher-energy state to a lower energy statethe complete equation:∆ E=RH(1ni2−1nf2)Solar System alignment of atom:- the electrons can only orbit at fixed radii from the nucleus. So the nucleus acts as the sun and the electrons are the planetsPredict wavelength (frequency) of electromagnetic radiation emitted (or absorbed) for transitions of hydrogen atom:∆ E=RH(1ni2−1nf2)λ=hc∆ E-example 7.4Electronic Transitions:-when an electron is at n=1 it is at its most stable state, or lowest energy state, the ground state-the stability diminishes as the electron hops up to level 2,3, these are excited statesDeBroglie’s relationship of wavelength of particles:-electrons/ particles have wavelike properties, behave like standing waves- have constructive interference and destructive interferenceλ=hmu-example 7.5Heisenberg Uncertainty Principle- it is impossible to know simultaneously both the momentum (p which = mass x velocity) and the position of a particle with certainty; answer to the problem of trying to locate a particle in a waveBohr’s orbits- are fixed around the nucleus in a circular formationOrbitals-do not have a defined shape, but have different shapes for each orbitalElectron density- gives the probability that an electron will be found in a particular region of an atom4 quantum numbers-describes address of electron-n- principal quantum number-determines the energy of an orbital,-l- angular momentum quantum number, tells shape of the orbital, equal to between 0 and n-1l=between o∧n−1-ml−¿ magnetic quantum number,orientation of the orbital in spaceamount of values possible for ml=(2 ×l)+1-ms−¿ electron spin quantum number, which possible spinning motion the electron takesms=+12∨− 12l quantum number: all the orbitals differ in size as energy level changes. (larger #= larger size)s=0, spherical shapep=1, two lobes on opposite sides of the nucleusd=2, 4 lobes on mostf=3Orbital letter for l Quantum # associated# of orbitals # of electronss o 1 2p 1 3 6d 2 5 10f 3 7 14Orbitals in order of increasing energy:1s,2s,2p,3s,3p,4s,3d,4p,5s,4dFilling order of electrons:Pauli Exclusion Principle- No 2 electrons can have the same 4 quantum numbers, thus no 2 electrons occupy same
View Full Document
Unlocking...