American Chemical Society Cumulative Exam (Chapters 5-7)

Chapter 5 • Ideal gas law (density, pressure, volume, and molecular weight) • Solving stoichiometry problems involving gases. • Calculating partial pressures and mole fractions. • States of matter/Solutions Notes: 1) gas= molecules/ atoms in constant random motion a. fills the container it occupies b. low density c. compressible d. mixtures are homogeneous 2) ideal gas assumption= often intermolecular forces are essentially negligible, size of molecules can often be ignored a. gases are measured using mass, volume, pressure and moles b. pressure= measure of total amount of this push exerted by gas molecules hitting the entire surface at one instant i. push on the surface (force) ii. force exerted per unit area of surface by molecules in motion 3) Gas Laws a. Empirical Gas Laws i. Boyle’s Law= volume varies inversely with pressure at a given temperature ii. Charles’ Law= volume at constant pressure is proportional to its absolute temperature b. Combined Gas Law= if P,V, and T are changing their combined relationship is (PiVi)/Ti = (PfVf)/Tf c. Avogadro’s Law= equal volumes of any two gases at the same T and P contain the same number of molecules i. volume is proportional to the number of moles d. Ideal Gas Law combines the three proportionalities i. PV=nRT e. Dalton’s Law= sum of pressures of all different gases in a mixture equals the total pressure 4) Partial Pressures of Gas Mixtures a. mole fraction= fraction of moles in A in the total moles of the mixture b. real gases don’t follow PV=nRt perfectly i. Van der Waals corrects for the nonideal nature of real gases c. kinetic molecular theory= simple model based on the actions of individual atoms i. volume of particles is negligible ii. particles are in constant motion iii. no inherent attractive or repulsive forces iv. average KE of particles is proportional to its temperature v. diffusion= transfer of gas through space over time vi. effusion= transfer of gas through a membrane or orifice 1. Graham’s law= rate of effusion of diffusion is inversely proportional to the square root of its molecular mass vii. as absolute temperature increases so does average velocity (distribution of function “spreads out” thus resulting in more water molecules with faster speeds) viii. in order to have the same average KE, heavier molecules must have a slower average speed Chapter 6 • Exothermic/endothermic processes • Calculating heat (or DH) of rxn. from stoichiometry. • Relating heat, specific heat capacity, mass, and DH (pay attention to units) • Thermochemistry Notes: 1) energy of a system= its capacity to do work a. work is done to achieve motion against an opposing force b. when a system changes energy due to difference in temperature between the system and its surrounding heat is exchanged i. heat is related to temperature ii. thermal motion= disorderly motion 2) exothermic process= chemical reaction/ physical change where heat is evolved a. “out of” a system b. deltaq is negative 3) endothermic process= chemical reaction/ physical change where heat is absorbed a. “into” a system b. deltaq is positive 4) thermodynamics= the relationship between heat and other forms of energy a. “system” is the part we are interested in i. boundary can be physical or imaginable, permeable or impenetrable to water, conducting or insulating, and rigid or flexible 5) thermochemistry= study of quantity of heat absorbed or evolved from chemical reactions a. energy= capacity to move matter b. chemical energy= energy stored within the structure of a molecule or atom c. kinetic energy= energy of motion or energy being transferred d. potential energy= energy stored in an object or associated with the composition or position of the object e. internal energy= sum of the kinetic and potential energy of the particles making up a substance f. law of conservation of energy= energy cannot be created or destroyed i. energy can be transferred between objects ii. energy can be transformed from one form to another g. Measurements of energy i. joule= amount of energy needed to move a 1kg mass a distance of one meter ii. calorie= amount of energy needed to raise one gram of water by one degree C 1. 1 cal= 4.184 J h. conservation of energy requires that total energy change in the system and the surrounding must be 0 i. 1st law of thermodynamics= law of conservation of energy 1. internal energy of an isolated system is constant ii. state function only depends on initial and final conditions not on the process used q (heat) system gains heat energy (+) w (work) system gains energy from work (+) delta u system gains energy (+) system releases heat energy (-) system releases energy by wok (-) system releases energy (-) 1) q (heat energy)= energy that flows into or out of a system because of a difference in temperature between the system and its surroundings a. heat= exchange of thermal energy between the system and its surroundings i. exchange occurs when system and surroundings have different temperatures 1. heat flows from high temperature to low temperature b. calorimetry= calculation of the amount of heat from temperature change c. heat capacity= quantity of heat required to raise the temperature by one degree C d. specific heat capacity= heat required to raise the temperature of 1 gram of a substance by 1 degree C e. thermal equilibrium= heat flows from high to low temperature until objects reach equilibrium f. calorimeter= device used to measure the heat absorbed or evolved during a physical or chemical change g. enthalpy (state function)= a property of a system that depends only on its present state and is independent of any previous history of the system h. endothermic reaction= heat transfers from surroundings to a system i. exothermic reaction= heat transfers from system to surroundings j. calorimetry at constant pressure= reactions done in aqueous solutions are at constant pressure (open to the atmosphere) i. calorimetry is often nested foam cups containing the solution 2) determining delta Hr(direct method)= law of summation of heats of formation a. the enthalpy of a reaction is equal to the total formation energy of the products minus that of the reactants 3) when looking for enthalpy: a. calculate heat absorbed by calorimeter b. calculate heat per mol 4) standard enthalpies of formation= 1 atm and 25 degrees C a. enthalpy change for the formation of one mol of a substance in its standard state form its component elements in their standard state 5) Hess’s Law= delta H (overall reaction) a. for a chemical equation that can be written as the sum of two or more steps, delta H for this equation is then the sum of enthalpy changes for the individual steps b. 4 Rules: i. phases of reactants and products are important ii. temperature of the reaction is important iii. if you reverse the reaction the sign of delta H changes iv. if the reaction is multiplied then delta H is also multiplied Chapter 7 • Relating wavelength and frequency of light (in terms of energy, color, …) • Calculating the energy of a photon, electron, (wave-particle duality) • Rules for quantum numbers. • Ground states Notes: 1) electromagnetic radiation= type of energy embodied in oscillating electric and magnetic field travelling through space a. light is a wave, can be diffracted and has constructive and destructive interference b. light= electromagnetic wave i. wavelength (nm)= distance between any two adjacent identical points ii. frequency (Hz)= number of wavelengths that pass a fixed point per second c. electromagnetic spectrum= range of wavelengths and frequencies of electromagnetic radiation i. visible light extends from the violet end to red end d. blackbody radiation= when you heat a solid it can emit radiation e. Planck’s quantum theory= energy of atoms and molecules take only discrete quantities i. energy is multiples of h(frequency) ii. atoms of a solid oscillate with a certain frequency 2) photoelectric effect= ejection of electrons from the surface of metals by radiation a. no electrons ejected unless frequency exceeds some threshold b. kinetic energy increases linearly with frequency but independent of intensity c. an electron is ejected when struck by a single photon (behaves like a particle) 3) Bohr’s Theory of Hydrogen Atom a. Bohr’s postulates: i. Energy level= an electron can only have specific energy levels in an atom ii. transition between energy levels= an electron can change energy levels by a “transition” from one energy level to another b. when an electron undergoes a transition from a higher energy level to a lower one, the energy is emitted as a photon i. elementary unit of light (photon) is a particle ii. light exhibits interference (it is a wave) c. electron diffraction= electrons present an interference pattern demonstrating wave-like behavior i. 2 electrons do not interfere with each other, one electron interferes with itself 4) deBroglie proposed that particles could have wave-like behavior and he predicted that the wavelength of a particle was inversely proportional to its momentum a. standing waves= only certain wavelengths can occur on a string i. if an electron behaves like a standing wave in a hydrogen atom, the length of the wave must exactly fit the circumference of the orbit b. energy of an electron depends on its “residence” in certain orbitals i. shell in a certain distance from center, subshell in a certain shape, subshell with an orientation and electrons spin direction 5) electrons are described by 4 Quantum numbers: a. principal qn (n)= energy i. principle qn= the “shell number” where an electron resides ii. n= 1,2,3,... iii. the smaller “n” is, the smaller the orbital and lower the energy of the electron b. angular momentum qn (l)= shape i. angular momentum qn= distinguishes “sub-shells” in a given shell that have different shapes 1. each main shell is divided into subshells with a distinctive shape 2. l= any integer from 0,1,...,(n-1) 3. subshells are denoted by numbers a. s=0, p=1, d=2, f=3, g=4 i. s= spherical (1) ii. p= dumbbell (3) 4. d= cloverleaf and dumbbell (5) c. magnetic qn (mi)= orientation i. magnetic= distinguishes orbitals in a subshell that have different shapes and orientations in space 1. each subshell is subdivided into orbitals capable of holding a pair of electrons 2. can be any integer from -l to l 3. each orbital within a subshell has the same energy d. spin qn (ms)= spin i. spin= two possible spin orientations of electrons residing in a given orbital 1. each orbital can hold only two electrons whose spins must opposed one another 2. equal to +/- (½)