Chapter 41-43 Book Notes
Chapter 41-43 Book Notes Chem 143
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This 6 page Class Notes was uploaded by Cassidy Zirko on Saturday January 30, 2016. The Class Notes belongs to Chem 143 at University of Montana taught by Dr. Cracolice in Spring 2016. Since its upload, it has received 100 views. For similar materials see General Chemistry 2 in Chemistry at University of Montana.
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Date Created: 01/30/16
Chem 143, Prof. Cracolice, Week 1 Chapter 41: Why do some Solution Properties Depend only on the Number of Dissolved Particles? 1/25/16 41.1 Why do Some Substance Properties Depend only on the Number of Dissolved Particles? Ideal Solutions no interaction among dissolved solute particles Physical properties of solution differ from physical properties of its components Dilute solutions compare properties of solution with properties of solvent o 1. Differences between value of property of solution and value for pure solvent is proportional to concentration of solute o 2. Concentration on which value of property depends must be express in number of particles—doesn’t matter if its ionic or molecular Colligative property depends entirely on concentration of solute particles in the solution and has nothing to do with what they are (second property of dilute solutions allows this classification) How is the Vapor Pressure of a Solution Affected by the Number of Dissolved Particles? o Quantity of dissolved solids in solution increases small decrease of vapor pressure o Change in vapor pressure (VP) occurs when solute is added to solvent ∆ P change∈pressure ) o VP of pure solvent VP of solution= o ∆ P ∝ X , X fraction of solution made up, mole fraction solution o Grater quantity of solute, greater change in VP o Mole Fraction number of moles of a component of a mixture divided by the total number of moles of all components X= molescomponent1 =mole fractionof component1 o Σmolesof allcomponentsaddedtogether o Sum of mole fraction of all components of any mixture must be equal to 1 o In dilute solutions change in some properties is ∝ to concentration of solute particles o Proportionality constant is the vapor pressure of pure substance, P o ∆ P=P° X Solution,mole fraction o Raoult’s Law vapor pressure of a solution is proportional to the mole fraction of the solvent, which is the solution component responsible for vapor pressure o P ° is gather from the table in the data pack, find temperature and corresponding Vapor pressure in mmHg Why is the Vapor Pressure of a Solution Lower than the Pressure of the Pure Solvent? Chem 143, Prof. Cracolice, Week 1 o Entropy measure of energy dispersal at the molecular level, more ways to disperse energy at the molecular level entropy increases o Entropy increase as the substances changes from a liquid to a gas Ex. as water evaporates, entropy increases o Number of ways to disperse energy of the solvent increases when solution is formed o Energy is more dispersed in a larger volume because the density of the number of ways of dispersing energy increases o Entropy of solution is greater than the entropy of the pure solvent o Vapor pressure of a solution is lower than the vapor pressure of corresponding pure solvent How is the Boiling Point of a Solution Affected by Number of Dissolved Particles? o Boiling Point increase with increasing concentration o Boiling Point Elevation ∆ T b change in boiling point, difference between a solution and the corresponding temperature for boiling the pure solvent is proportional to the molal concentration of the solute (moles of solute per kilogram of solvent), ∆ T b =K b o K bolal boiling point elevation proportionality constant in ℃ /kg, o T bboiling point elevation colligative property o Molality, m number of moles of a solute dissolved in 1kg of solvent, molesolute m= kgsolvent o molality isn’t very convenient because units can be measure in a solution that is already made o as volume of a solution changes by heating or cooling, the mo9laity changes How is the Freezing Point of a Solution Affected by the Number of Dissolved Particles? o Freezing point of solution decreases with increasing concentration o When solution freezes, solid forms pure solvent o Solid solvent + heat liquid solvent o Heat is removed from the system during the freezing process o ∆ T change in freezing temperature, freezing point depressing f o ∆ T ∝ m ∆ T = Km f f f o K –fmolal freezing point depression constant How Can Changes in Boiling and Freezing Points be used to determine Molar Mass? ∆T f (¿b) o Can find molality from m= K which then is expressed as mol solute/ kg f (¿b) solvent Chem 143, Prof. Cracolice, Week 1 o Using molality as a conversion factor between moles of solute and kilograms of solvent, find number of moles of solute o Using the defining equation for molar mass, MM=g/mol, calculate molar mass of solute How are Boiling and Freezing Points Affected by Ionic Solutes? o For ideal solutions, both solute and solvent are volatile o Vapor pressure of a solution is the sum of the partial vapor pressure of the solute ° ° puls that of the solvent,solnX1 1 X 2 2 … o Colligative properties concern only the number of solute particles, ionic or molecular o Ion Multiplier, i equal to the number of moles of ions resulting from the dissociation of one mole of solute ∆ ∆ o Tf= iKmf(freezing) or T b= iKbm (Boiling) o i number of total compounds in a molecular formula ex. NaCl i=2 o most solutions don’t conform precisely with calculated values o solvent and/or solute particles interact with each other or themselves o interactions are electrical in nature o more dilute solution, eater interaction between particles approaches ideal character Chapter 42: How does Particle Size Affect Solutions? 1/27/16 42.1 What is Osmosis? Semipermeable membrane having very ting submicroscopic spores Individuals are always in constant motion Molecules continue to move through the membrane in both directions Dynamic Equilibriumopposite changes occur at the same rate Concentration of particles in dissolved water causes colligative Osmosis flow of any solvent through a semipermeable membrane from a dilute solution or pure solvent to a more concentrated solution Osmotic pressure π pressure required to restore equilibrium in the rates of flow between the two sides of a semipermeable membrane How is Osmotic Pressure Determined? o Colligative property proportional to molar concentration o π=RTiM , mass and molar mass can be substituted in for M o Equation can be sued to estimate moles or molar mass of a large complex unknown solvent molecules o Same units as ideal gas equation Chem 143, Prof. Cracolice, Week 1 o You wont necessarily have a wrong answer if osmotic pressure is very large o Super important because cell membranes are semipermeable a shit in osmotic pressure can be fatal o Isotonicsolution with same concentration o Hypertonic solution which has a concentration greater than the internal of the cell o Hypotonic solute concentration that is less than the cell 42.2 When is a Solution No Longer a Solution? Colloid glue, substances that are partially transparent and has visible particles in it Tyball Effect sunlight scattered by colloidal particles in air or water Large particles cause light to scatter and don’t form homogenous mixture s What Types of Colloids Exist? o Occur in all states of matter o Aerosol when a liquid or solid is dispersed in a gas o Sol solid dispersed in a liquid o Solid sol solid dispersed in a solvent o Foam gas is dispersed in a liquid or solid o Emulsion mixture of 2 or more immiscible liquids o Gel liquid dispersed in a solid o Hydrophilic dispersed phase molecules are attracted to water o Hydrophobic colloidal particles separate from water o Electrical double layer surrounded colloid particles caused by large colloidal molecules having many electrons o Absorb ions of the colloidal particles that adhere to the surface of the water molecules because of ions having induced dipole attraction o Large outer shell surrounding the colloidal particles repelled by the outer shell of other colloidal particles o Surfactants, surface active agents large nonpolar section and a polar head and at one end of the molecules o Nonpolar tail is attracted to hydrophobic colloid particles o Polar heads attracted to water molecules o Colloidal substance becomes stabilized in the water How are Colloidal Particles Removed from Dispersions? o Dialysis using semipermeable membrane to separate colloidal particles from solution o Agglomeration, coagulation or flocculation causes dispersed particles to come into contact so that they are attracted to each other through intermolecular forces o with no ionion repulsion hydrophobic colloidal particles can agglomerate and form particles that are large enough to filter out Chem 143, Prof. Cracolice, Week 1 Chapter 43: What is the Relationship Among Reaction Speed, Concentration and Stoichiometry? 1/29/16 Kinetics investigates speed, or rate, of chemical reactions Reaction Mechanism closely related knowledge of events during a chemical reaction some reactions are very slow, some are fast 43.1 What are Major Influences on Reaction Speed? States of reactants: depends on frequency of molecular collisions more particles, more collisions fast reaction o Solids have less surface area less space for collisions so slower reaction o Homogenous phase states of reactants are all the same o Heterogeneous phase reactants are in different phases Concentration of reactants: higher concentration means more particles in a given space and allows for more frequent collisions Reaction temperature: chemical reactions occur faster at higher temperatures (pressure cookers) Addition of a catalyst: catalyst substance that increases speed of reaction because it lowers the energy needed for the reaction initiation o Catalyst is either nonparticipant or regenerated o Enzyme molecule that acts as a biological catalyst 43.2 How are Reaction Speeds Measured? Speed quantity that states how fast something is moving Rate quantity of one thing considered in relation to another measure quantity u Reaction rates change in concentration of a species per unit of time Reaction rates expressed in terms of reactant for product Simple reaction: decomposition of reactants formation of products, RP −∆ R ] ∆[P ] o Rate= ∆T = ∆T , square brackets indicate concentration Rates expressed as positive quantities but final concentrations are always less than initial concentrations hence the use of the negative sign on the reactants How are Reaction Rates Calculated? o Spectrophotometer measures color intensity electronically o Average rate defined as the average rate of change in concentration of a species over a specified time interval ≡− ∆ R ] | [R| average rate ∆T or ∆T Chem 143, Prof. Cracolice, Week 1 Instantaneous Reaction rate at a particular instant in time, found using calculus Need straight line that touches the concentration in question (tangent line), time curve at point of interest then find slope to get instantaneous rate How Reaction Rates Related to Reaction Stoichiometry? o Rate of chemical reaction is based on which reactant or product is measured o aA+bB cC+dD (general equation) |∆[A]| |∆[B | ∆[ ] ∆ [ ] o Rate = a∆T = b∆T = c∆T = d ∆T o Rate of decomposition of reactants is always negative without absolute value signs o Use quantity algebra, don’t need the negatives or absolute value sign on reactants to go from one species to another