Chemistry Exam 2 Study Guide
Chemistry Exam 2 Study Guide CHEM 1120
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This 11 page Study Guide was uploaded by Anzlee on Thursday October 6, 2016. The Study Guide belongs to CHEM 1120 at Middle Tennessee State University taught by Ngee S Chong in Fall 2016. Since its upload, it has received 25 views. For similar materials see General Chemistry II in Chemistry at Middle Tennessee State University.
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Date Created: 10/06/16
EXAM 2 STUDY GUIDE Prerequisites to Review: *Remember how to do Lewis Dot Structure *Review of Group Names on Period Table: 1A/1- Alkali Metals 2A/2- Alkali Earth Metals 6A/16- Chalcogens 7A/17- Halogens (Diatomic) 8A/18- Noble/Inert Gases *States at Room Temperature: Gas: Mg and Br Liquid: Fr, Cs, Gr, and Rb Solid- all others *Solubility: -Solute- what’s going into solvent; smaller number of moles -Solvent- dissolves solute; larger number of moles -Solubility- maximum amount of substance it can dissolve at a given volume -Miscible- liquids are mutually soluble in any proportion Chapter 6 Intermolecular Forces • Interactions between nonpolar molecules o Dispersion- momentary shift in electron density o Dispersion (London) forces- caused by presence of temporary dipoles in molecules (weakest bond) § Larger molecules usually solid, then liquid, then gas o Temporary (induced) dipole- separation of charge produced in atom or molecule by a temporary uneven distribution of electrons (middle strength) § May be caused by a reaction between a polar and nonpolar molecule o Polarizability- the ease that an electron cloud in a molecule, ion, or atom can be distorted, inducing a temporary dipole § Larger molecules/elements have higher polarizability because intermolecular forces are weaker Factors Affecting Strength of Dispersion: • Size of atom/molecule- larger are more polarizable because the outer valence electrons are being weakly pulled by the positive nucleus; dispersion increases with polarizability o Molar mass size is directly correlated with boiling point/melting point o RVP: reid vapor pressure of gasoline regulated by Environmental Protection Agency • Shape of molecules- increased surface area causes increased interactions and stronger interactions, which affects physical and chemical properties; linear molecules have higher dispersion than branched molecules with similar molecule weight o Constitutional isomers (structural isomers)- molecules that have the same formulas, but different connections between atoms; differently arranged o Larger surface = larger dispersion = higher boiling point o Viscosity- measure of resistance of a fluid to flow (cP- centipoise unit) § factors: molecular shape, molar mass, and temperature § higher molar mass= higher viscosity Interactions Involving Polar Molecules: • Dipole-dipole attraction- the force between polar molecules • Hydrogen bond- strongest dipole-dipole interaction o occurs between hydrogen bonded to a small and highly electronegative element (F, O, N) and an atom of O or N in another molecule o Ex. between complementary sites on double stranded DNA- between A and T or C and D o All alcohols; all amino acids can have hydrogen bonds o More hydrogen bonding = higher boiling point • Boiling points of Binary Hydrides- when boiling points are related to attractive forces, be able to determine boiling point order • Ion-Dipole- force between an ion and a molecule with a permanent dipole • Sphere of hydration- water molecules surrounding ion in aqueous medium Solubility: • Depends on relative strength of interactions between molecules • Ionic/polar solutes are soluble in polar solvents o No solution if different forces • Nonpolar solutes are soluble in nonpolar solvents o No solution if different forces • More than one force may need to be examined o Solubility decreases as hydrogen bonding energy decreases and dispersion increases • Hydrophobic- repels water; lowers solubility • Hydrophilic- attracts water; heightens solubility Physical States: • Factors that affect state: intermolecular forces, temperature, pressure • Phase diagram o Graphical representation of substance’s states depending on temperature and pressure o Lines represent points where two states on either side coexist in equilibrium o Triple point- where all phases exist at same time o Critical point- where liquid and gas have same density o Supercritical fluid- substance above critical temperature and pressure Properties of Water: • Surface tension- energy needed to separate molecules of the liquid’s surface; directly correlates with strength of intermolecular forces • Cohesion- interactions between same particles • Adhesion- interactions between different particles • ex. meniscus § concave- adhesive forces greater than cohesive forces § convex- cohesive forces greater than adhesive forces • Capillary action- liquid can spontaneously flow against gravity; involves adhesive and cohesive forces • Density of water- decreases as a solid o Important for aquatic ecosystems Chapter 11 Properties of Solutions • Enthalpy of Solution depends on: o Energies that are holding the solute ions in the crystal lattice o Attractive force holding solvent together o Interactions between solute ions and solvent molecules • Lattice energy- energy released when 1 mole of the ionic compound forms from free ions in gas phase; energy released when crystal lattice forms (positive) • ΔH ion-ionenergy required to remove ions from crystal lattice (negative) • Born-Haber cycle- series of steps with change of energy (ΔH) that describe the formation of an ionic solid from its elements (sublimation, bond breaking, ionization, electron affinity, formation) Isoelectronic- same electron configuration when electrons are lost or gained Na is isoelectronic with Ne Vapor Pressure: • Pressure exerted by gas in equilibrium with liquid; evaporation and condensation rates are equal • Normal boiling point- ambient pressure must be standard pressure • Factors affecting vapor pressure: o Temperature/surface area; overcoming intermolecular forces o Presence of nonvolatile solute- affects rate; decreases vapor pressure o Clausius-Clapeyron Equation: related vapor pressure with temperature of substance to its heat of evaporation • Fractional Distillation- separate a mixture of compounds based on their differing boiling points o More volatile components have enriched vapor pressure • Raoult’s Law- total of overall pressure is equal to the sum of each individual pressures of the components, in an ideal solution • Real vs. Ideal solutions- due to differences in solvent-solvent and solvent-solute interactions Osmosis: • Fluid flows across a semipermeable membrane to balance the concentration of that fluid on both sides • Osmotic pressure- pressure applied to membrane to stop flow of solvent o Formula: iMRT • Hypertonic state- water migrates out • Hypotonic state- water migrates in • Isotonic state- water concentration is at equilibrium o Cells within body should be isotonic • Reverse osmosis- solvent pushed through membrane, leaving higher concentrated solution behind o Ex. water distillation/purification Chapter 11 Online Homework Samples: 8, 16, 18 Test 2 Material Thermodynamics Spontaneous Reactions: • Most are exothermic- ∆H < 0 o ex. combustion • Endothermic spontaneous reactions- ∆H > 0 o particles in product are more spread out than starting reactants o ex. cold packs • Gas à liquid à solid o Heat is released • Solidà liquidà gas o Heat is put in Entropy: • Entropy (S)- how dispersed energy is in a system at a temperature o Effected from molecular motion and volume o Increases from: increasing temperature, volume, complexity of structure, and independent particles o Can never be negative (only zero if K is zero) • Second Law of Thermodynamics- entropy of universe is equal to the entropy of the system and the surroundings (greater than zero) • Entropy and microstates o Motion of molecules in quantized- different molecular states are separated by energies o Energy state/energy level- allowed value of energy o Microstate- distribution of particles within energy level • Boltzmann Equation: -23 k Bn W o kB= 1.38*10 J/K o W = number of microstates • Third Law of Thermodynamics- perfect crystal provides baseline for entropy because at absolute zero (0 K or -273 C), the entropy is zero 0 • Standard Molar Entropy (S )- absolute energy of 1 mole in standard state (298 K and 1 bar of pressure) o Found from how much heat energy a substance must have to change temperature by one value • Types of Molecular Motion (increases with increasing temperature): o Translational- movement through space o Rotational- perpendicular spinning motion around axis o Vibrational- movement of atoms to and away from each other • Entropy Change: ∆S rxn= ∆S sys S final Sinitial • Isothermal Process o ∆S = q rev o qrev= flow of heat for reversible process • Gibbs Free Energy (G)- maximum energy released that is available to do work o constant temperature and pressure o ∆G = ∆H -T∆S o ∆H = ∆G +T∆S o efficiency = work done divided by energy produced Chapter 13: Chemical Kinetics • Kinetics- rate of the change of concentrations of substances in chemical reactions o Reaction Rate- how quickly reaction occurs; concentration change over time o Reactant molecules must collide with sufficient energy (above activation energy) to form products o Factors effecting rate- physical state, concentration, temperature, and catalysts o Rate constant = k o Rate Law- defime relntionship between rate of reaction and concentrations § k (A) (B) • m and n are reaction order with respect to A and B (usually 1 or 2; never 3 or above) • m + n is the overall order of reaction o Reaction order- number defining dependence of rate on concentration • Photochemical Smog- internal combustion engines produce compounds that interact with sunlight, producing a mixture of gases Half-Life (t 1/2 • Time of a chemical reaction where the concentration of the reactant decreases by half o ln A/t =0-0.693 = -kt o t1/2= 0.693/k § Example: An isotope has a half life of 14.3 days. How long does it take for 95% of the sample to decay? Activation Energy (E ) a • Energy of molecular collisions reactants must have to break bonds and therefore form products • Arrhenius Equation o k = Ae -Ea/RT § A- collision frequency factor § R- universal gas constant (note units) § T- temperature in kelvin Reaction Mechanisms • Steps that show how reaction occurs (molecular level) • Needs to be consistent with the rate law o Elementary Step- single process o Intermediate- species produced in one step and used in the next step o Molecularity- number of ions, atoms, or molecules in an elementary step
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