CHM 1045 Spring 2014 Study guide Exam 3 Chapter 6 Endothermic 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 system H U PV Calorimetry measurement of heat changes Heat 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 ms q ms t t t final tintial Constant 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 q rxn DOES NOT H because under constant volume q cal C cal t example 6 6 Constant Pressure Calorimeter used to determine the heat changes for noncombustion reactions q rxn H because under constant pressure example 6 7 and 6 8 Standard enthalpy of reactions the enthalpy of a reaction carried out at 1 atm equation n H f products n H j reactants example 6 10 Hess 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 9 Planck s Theory and Classical Physics Chapter 7 classical physics thought that energy was continuous and any amount could be released Planck discovered that atoms and molecules emit energy only in certain discrete amounts or quanta Wavelength distance between identical points in successive waves Amplitude A vertical distance from middle of the wave to peak or trough Frequency 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 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 components 1 electric field 2 magnetic field 2 components have the same wavelength and frequency but travel in different planes Electromagnetic 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 h c so E h c h being Planck s constant example 7 2 Photoelectric 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 h is to the binding energy of 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 h 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 3 Bohr s model of the atom substances emission spectra continuous or line spectra of radiation emitted by 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 R H 1 n2 2 E R H 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 state the complete equation 1 2 ni 1 nf 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 planets Predict wavelength frequency of electromagnetic radiation emitted or absorbed for transitions of hydrogen atom 1 nf 1 2 ni E R H 2 hc E example 7 4 Electronic Transitions state the ground state h mu when an electron is at n 1 it is at its most stable state or lowest energy the stability diminishes as the electron hops up to level 2 3 these are excited states DeBroglie s relationship of wavelength of particles electrons particles have wavelike properties behave like standing waves have constructive interference and destructive interference example 7 5 Heisenberg 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 wave Bohr s orbits are fixed around the nucleus in a circular formation Orbitals do not have a defined shape but have different shapes for each orbital Electron density gives the probability that an electron will be found in a particular region of an atom 4 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 1 l between o n 1 ml magnetic quantum number orientation of the orbital in space amount of values possible for ml 2 l 1 ms electron spin quantum number which possible spinning motion the electron takes 1 2 1 2 ms l quantum number all the orbitals differ in size as energy level changes larger larger size s 0 spherical shape p 1 two lobes on opposite sides of the nucleus d 2 4 lobes on most f 3 Orbital letter for l of orbitals of electrons s p d f Quantum associated o 1 2 3 1 3 5 7 Orbitals in order of increasing energy 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d Filling order of electrons 2 6 10 14 Pauli Exclusion Principle No 2 electrons can have the same 4 quantum numbers thus no 2 electrons occupy same space paramagnetic contain unpaired electron spins and are attracted by a magnet like this they r in 2 separate orbitals odd of electrons diamagnetic do not contain net unpaired spins and are slightly repelled by a magnet like this even of electrons Hund s Rule
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