Chemistry Exam 2 Study Guide
Chemistry Exam 2 Study Guide chem 10061-001
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This 7 page Study Guide was uploaded by Jessica Brown on Thursday March 17, 2016. The Study Guide belongs to chem 10061-001 at Kent State University taught by David bowers in Summer 2015. Since its upload, it has received 108 views. For similar materials see general chemistry 2 in Chemistry at Kent State University.
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Date Created: 03/17/16
Exam 2 Study Guide Chapter 13 1. Solute particles separate a. Endothermic process 2. Solvent particles separate a. Endothermic process 3. Solute and solvent particles mix a. Exothermic process ∆H soln =∆H solute + ∆H solvent +∆H mix Hsoln: the total enthalpy change o Can be endothermic or exothermic Endothermic if Hmix is less then Hsolute + Hsolvent Exothermic if Hmix is greater than Hsolute + Hsolvent Heat of Hydration The process of surrounding solute with solvent o Gives you ∆H solvation Solvating with H2O o ∆H hydration Remember that solid ionic solutes must be separated into its gaseous ions o Recall Lattice Energy o Ionic compound dissolving in H2O gives you ∆H solute = -∆H Lattice o If∆H hydration (exothermic) >∆H lattice (endothermic) then ionic compound dissolves ∆H hydration follows trends based on ions charge density o Charge Density: the ratio of charge to volume Higher charge density the more negative (exothermic) the ∆H hydration It is more negative for… Smaller ions Ions with a higher charge Cations < Anions Be sure to check out Enthalpy diagrams Entropy Entropy: random motion Does not support order o Getting and keeping order requires work (in form of energy) Thus why universe favors entropy—less work because no order! Entropy can be used to determine the solubility of a solute o ∆S > 0 Exothermic (+) spontaneous o ∆S < 0 Endothermic (-) non-spontaneous o ∆H < 0 Exothermic o ∆H > 0 Endothermic Entropy and the States of Matter S gas > S liquid > S solid Solution Equilibrium: when solid is dissolving at the same rate of recrystallization Saturated: maximum amount at a given temperature Unsaturated: less then max When you add more solute it dissolves Supersaturated: More than saturated Very Unstable Temperature and Solubility Increase temperature increase kinetic energy has an effect on the forces present Solids: more soluble at higher temperatures o Heat encourages the molecules to break free from lattice Gases: decreased solubility at increased temperatures o Encourages molecules to overcome intermolecular forces and escape the solution as a gas Pressure and Solubility Solids & Liquids: little effect o This is because solids and liquids are already in a condensed state Gases : major effect o Increased pressure means increased solubility of gas Henery’s Law Expresses quantitative relationship between gas pressure and solubility Gas solubility (S gas) is directly proportional to partial pressure of gas Concentration: proportion of substance in mixture (intensive property) Extensive Property: depend on quantity of a mixture present Intensive Property: doesn’t depends on quantity of mixture present Ex.) density, color, melting/boiling point, temperature etc IMPORTANT EQUATIONS amount mol )solute Molarity (M) volume ( )olution MolesSolute Molality (m) Mass ( )solvent Masssolute Parts by Mass Mass solution VolumeSolute Parts by Volume Volume Solution molesolute Mole Fraction(X) molesolute+molesolvent Mass of solute Parts per million (ppm) x10 6 totalmass **All of these equations MUST be memorized. They are not given on the exam!** Colligative Properties Colligative Properties (collectively): depends only on the number of solute particles in solution and not on other properties of the solute 1. Vapor Pressure Reduction (∆P) 2. Boiling Point Elevation (∆T ) b a. Solution boils at a higher temperature then a pure solvent b. ∆T b K m b i. Where ∆T = b (sobution) – T (sobvent) ii. K = molal boiling point elevation constant b 3. Freezing Point Depression (∆T ) f a. Solution freezes at a lower temperature i. ∆T f K mf 1. Where ∆T = T (solvent) – T (solution) f f f 2. K f molal freezing point point depression constant 4. Osmotic Pressure (∏) a. Osmosis: process by which solvent flows through a semipermeable membrane from a dilute to a concentrated solution b. Semipermeable Membrane: allows water to enter but not solute molecules c. Osmotic Pressure: applied pressure required to prevent the net movement of water from the solvent to the solution d. Two solutions needed i. One that is higher in concentration (more dissolved) and 1 more dilute (less dissolved solute) e. Quantifying Osmotic Pressure i. ∏ = MRT 1. M= molarity 2. R= 0.08206 L atm/ mol k 3. T = Kelvin Recall Electrolyte: substance that conducts electricity when dissolved in H2O Strong Electrolyte: solute that dissolves completely into ions in solution Weak Electrolyte: Solute that only partially dissolves into ions Underlying Theme of Colligative Properties Properties come about because solute particles can’t move between phases Presence of solute decreases the mole fraction of the solvent, this lowers the number of solvent particles that escape the solution per unit time o This lowering requires a new balance in the numbers of particles that move between the phases per unit time—this is what causes colligative properties All colligative properties can be used to calculate the molecular weight o Osmotic pressure is the most reliable due to it having the largest changes and the most accurate values Nonvolatile, Nonelectrolyte solutions Not ionic and doesn’t dissociate Vaper pressure lowering and Raoult’s Law o Nonvolatile solute is dissolved in a liquid causing the vapor pressure of liquids are reduced Entropy is responsible Entropy increases as liquid turns to gas S increases for formation of a solution Less solvent molecules need to vaporize to reach the same entropy without a solute Psolution=Pressure of a solution Psolution = Xsolvent ( P solvent) 0 P solvent= vapor pressure of pure solvent ∆P = Xsolute (P solvent) ∆P= P solvent – P solvent Strong Electrolyte Solutions (ionic or strong acid and bases) Solute formula designates the number of particles Multiply by van’t hoff factor o Measured value for electrolyte solution/ expected value for nonelectrolyte solution o For these replace i (van’t hoff factor) infront of all the equations for the colligative properties Rate Law Rate law only includes reactants Balancing coefficients aren’t always equal to reaction orders! Rate Law Assumptions o Reactions products do not always show up in the rate law o Rate depends on concentration and temperature only Reaction order can only be determined with experimental data 1 order Rate is directly proportional to concentration o Ex.) Rate doubles when [A] doubles 2nd Order Rate is proportional to the square of concentration o Ex.) rate quadruples when [A] doubles 0 Order Reagent concentration has no effect on rate o Rate does not change when [A] doubles m n Rate = k [A] [B] Integrated Rate Laws Integrated Rate Law: gives understanding of how time and rate are related ** Look at equations for the orders!! These equations will be given but you must know which equation does to which order. Half Life: for a reaction is the time taken for the concentration of a reactant to drop to half its initial value Collision Theory A model that explains reaction rate as based on the number of solute particles o Molecules must collide to react—at the right speed and right orientation basis of rate law o Higher concentrations mean higher chances of collisions o Temperature is critical! Activation Energy (Ea): the minimum energy with which molecules must collide to react When particles collide effectively—they end up hitting the activation state. o The energy difference between the reactants and the activated state is the activation energy (Ea) for the reaction Lower Ea = a faster reaction Transition State Theory A model that explains how the energy of reactant collisions is used to form a “high energy transitional species” that can change reactant to product o Contains partial bonds Catalyst Lowers the activation energy which causes an increase in K and therefore causes an increase in rate Increases the forward and the reverse reactions Increases the rate but the catalyst is not consumed Not essential to the mechanism
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