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UI CHEM 1120 - Exam 1 Study Guide
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Chem 1120 1st EditionExam # 1 Study Guide Lectures: 1 - 12Lecture 1 (January 21)What are the 6 different types of intermolecular forces and describe eachIon-Dipole - force between ion and polar molecule with dipole momentHydrogen Bonding - force from attractions between molecules with H bondedto electronegative element (OH, HF, NH, etc)Dipole Dipole - polar molecules interact or become closeIon Induced Dipole - weak force from ion inducing dipole in an atom or non-polar molecule Dipole Induced Dipole - weak force from polar molecule influencing dipole in atom or nonpolar moleculeDispersion Forces - forces from induced dipoles attracting each other Explain the differences between a solute and a solvent, and saturated vs un-saturated vs supersaturatedSolute is the dissolved material, solvent is the dissolving agent, saturated is when a solution’s solvent holds as much solute as is possible (dissolved solute in equilibrium with solid solute particles), unsaturated is when there is less solute than can be dissolved in a solution, and supersaturated is when the solution’s solvent holds more solute than a saturated solutionDescribe the process of dissolution3 steps: 1) crystals separate into ions (endothermic) 2) water molecules sep-arate to create “holes” to accommodate ions (endothermic) 3) ions fill the holes created by the water molecules (exothermic) *Heat of Solution = HSOLUTE + HSOLVENT + HMIXLecture 2 (January 23) Describe the idea of entropyEntropy is a thermodynamic measure of the randomness or disorder of a sys-tem. In our world, we assume objects move from a higher energy level to-ward a lower energy level, and the same is true for chemical processes. Mostrelease more heat than they absorb, making them exothermic, although some can be endothermic. When entropy increases, the reaction is sponta-neous and vice versa.Name the five different concentration units and know how to complete prob-lems for each, including ppm, ppb, and vapor pressure loweringMolarity, M = moles solute/Liters solutionMolality, m = moles solute/kg of solventMass percent, m% component A = (mass of A/total mass of solution) X 100Volume percent, v% component A = (V of A/total V of solution) X 100Mole Fraction, X = moles of A/total moles of solutionppm = (mass A/total mass) X 10^6 ppb = (mass A/total mass) X 10^9Vapor pressure lowering, PSOLUTION = XSOLVENT + POSOLVENTExample: How many grams of glucose (C6H12O6) must be dissolved in 552 grams of water at 20 degrees C (v.p. = 17.5 torr) to lower its vapor pressure by 2.0 torr?Solution:The change in PSOLUTION = 2.0 torr, so 15.5 torr = XWATER x (17.5 torr)molar masses = 180.1559 g/mol and 18.02 g/mol(552 g water)/(18.02 g/mol) = 30.64 mol waterXWATER = (15.5torr/17.5 torr) = (30.64 mol water/30.64mol water + mol glu-cose)mol glucose =3.953(3.953 mol glucose x 180.1559 g/mol) = 712.3 g glucoseLecture 3 (January 26)Give the freezing point lowering and boiling point elevation equa-tions and know how to use each/what each component of the equa-tions mean△Tf = -ikf m i = van’t hoff factor (2 when a substance ionizes, usually 1)△Tb = ikb m m = molality kb and kf = boiling and freezing molal con-stantsExample: Vinegar is essentially a 5.0% (w/w) solution of acetic acid (HC2H3O2) in water. What is the freezing point of vinegar? kf = 3.90 (acetic acid), 1.86 (water) (units = degrees C/m)Solution: Assume 1 kg of solution= 0.95 kg water= 0.05 kg = 50 g acetic acid(50 g)/(60.05g/mol) = 0.8326 mol acetic acid molality = (0.8326 mol)/(0.95 kg) = 0.8764 m △Tf = -ikf m = (1.86)(0.8764) = -1.63 degrees CDescribe osmosis, give the osmotic pressure equation, and know howto apply this equation as well as what each component of the equa-tion meansOsmosis is the diffusion of a solvent (usually water) through a semi-perme-able membrane into a solution. Osmotic pressure (π) is the pressure result-ing from osmosis and equal to the minimum counter pressure necessary to prevent osmosis. π = MRT M=Molarity R=0.08206 T=KelvinLecture 4 (January 28)Explain how to find the van’t Hoff factor and why the actual values are slightly different than the expected onesTo find the van’t Hoff factor is pretty simple. It is equal to the moles of solute dissolved in a solution. For salts, you just take the number of ions over the formula units. NaCl splits into two ions; therefore, the van’t Hoff factor is two.The van’t Hoff factor usually ends up as 1 or 2 depending on if it dissolves into ions or not.Acknowledge the difference between a colloid and a suspension, and discusshydrophilic vs hydrophobic colloids A suspension is a heterogeneous mixture with dispersed particles larger enough to be seen and a colloid is a mixture with dispersed particles larger than a solution’s, but smaller than a suspension’s. For a hydrophilic colloid, the surface is hydrophilic while the core may be hydrophobic. The surface groups bond to water and they are large molecules. For a hydrophobic col-loid, it must be stabilized by absorbed ions on the surface, and these ab-sorbed ions interact with water and particles repel each other. The tail is hy-drophobic while the head is polar.Lecture 5 (January 30)For a generic reaction, describe how to find the rate law due to concentration, and the rates of each reactant and product mathematicallyIn most cases for a generic reaction, aA + bB ——> cC + dD, the rate law dueto concentration looks like: Rate = k [A]m[B]n Show the equations for average rate and instantaneous rate, and also show how to find the units of a rate, giving the units for first and second order rates.average rate = △[A]/△t instantaneous rate = slope of the tangent to the curve (rate at an arbitrarily short time)Units of rate = (units of rate constant)(units of concentration)order1st order rate units = s^-1 2nd order rate units = M^-1 * s^-1Lecture 6 (February 2)Explain the process of finding reaction order when given a set of data. Additionally, make a table of all the reaction orders and their corresponding units, rate laws, half life equations, etcWhen given a set of data, see where a set of concentrations doubles, triples, quadruples, etc, and then look at the corresponding rate constants. Comparethe ratio of how the concentrations change and how the rate laws change at the same time. If the ratio is 1:1, then the reaction is first order. If the ratio isnot affected by a concentration, then the order with respect to that


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UI CHEM 1120 - Exam 1 Study Guide

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