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Chemistry Exam 2 Study Guide

by: Jessica Brown

Chemistry Exam 2 Study Guide chem 10061-001

Marketplace > Kent State University > Chemistry > chem 10061-001 > Chemistry Exam 2 Study Guide
Jessica Brown

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About this Document

Conceptual material from exam 2
general chemistry 2
David bowers
Study Guide
Chemistry, General Chemistry, Science
50 ?




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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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