Chem 1212 Test 2 Study Guide
Chem 1212 Test 2 Study Guide CHEM1212
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This 17 page Study Guide was uploaded by Cheyenne Grooms on Sunday September 25, 2016. The Study Guide belongs to CHEM1212 at University of Georgia taught by Donald Wayne Suggs in Fall 2015. Since its upload, it has received 6 views. For similar materials see Freshman Chemistry II in Chemistry at University of Georgia.
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Date Created: 09/25/16
Chem 1212 Test 2 Study Guide T/Tr 3:30 – 4:45 End of Chapter 13 Chapter 15 Colligative Properties, Rate, and Equilibrium Chapter 13 Colligative Properties Colligative properties are physical properties that only apply to solutions Depend ONLY on the ratio of the number of particles of solute to the solvent o The more particles in solution will increase the effect on the specific property Does NOT depend on the identity of the solute 1. Boiling Point Elevation a. A solute mixed into a solution increases the boiling point elevation because the vapor pressure is lowered i. The more solute added = the higher the boiling point elevation and the lower the vapor pressure 2. Freezing Point Depression When a solute is dissolved in a solution it causes the freezing point of the liquid to decrease o The more solute in a solution = the greater decrease in freezing point! *If asked to order compounds from least to greatest boiling point elevation the compound with the MOST ions will have the HIGHEST boiling point elevation; if two compounds dissociate into the same # of ions the compound with the LARGEST MOLAR MASS will have the HIGHEST boiling point elevation *If asked to order compounds from least to greatest freezing point depression the compound with the most ions will have the GREATEST freezing point depression which means it will have the LOWEST final temperature. The compound with the LEAST amount of ions will have the LOWEST freezing point depression which means it will have the HIGHEST final temperature. Same rule applies here as it does in boiling point elevation if the compounds have the same number of ions. In the final temperature equations for boiling point elevation and freezing point depression…. i represents the Van’t Hoff Factor the Van’t Hoff Factor accounts for the number of ions an ionic compound dissociates into KEEP IN MIND that ionic compounds DO NOT dissociate perfectly like we were once told The Van’t Hoff factor will need to be calculated unless the problem specifically says NONVOLATILE NONELECTROLYTE (meaning the Van’t Hoff Factor will = 1 because the compound won’t dissociate) or if the problem states that the compound PERFECTLY ionizes or something along those lines (meaning that the compound would ionize as we would expect. For example NaCl Van’t Hoff factor would = 2 if this were the case. 1 Na and 1 Cl) In the Van’t Hoff Factor Equation Measured the value that was found during an experiment Calculated the value that was found by mathematically calculated using the weight of the solute to determine molality or the change in freezing point or boiling point *Be sure to account for the Van’t Hoff Factor when calculating the mols of an ionic compound ***Also, be sure to set up a molar ratio if finding the mols of a specific element in a compound for instance to find the mols of Cl- in NaCl2 you would first have to find the mols of NaCl2 then multiply by 2 because for every 1 mol of NaCl2 there are 2 mols of Cl- 3. Osmotic Pressure a. **** BE SURE TO PAY ATTENTION TO UNITS OF R VALUE AND UNITS GIVEN IN PROBLEM MUST MATCH IN ORDER TO CANCEL OUT!! i. If given a value in torr or mmHg be sure to convert to atm before plugging into your equation b. **** ALSO PAY ATTENTION TO WHAT UNIT THEY ASK FOR THE ANSWER IN AND BE SURE TO CONVERT TO THAT UNIT BEFORE PUTTING IN YOUR ANSWER i. 1 atm = 760 mm Hg and torr 4. Vapor Pressure Lowering a. Use Raoult’s Law to calculate (shows the amount that the vapor pressure lowers as a solute is added to a solution) b. Whenever a solute is added to a solution the vapor pressure will DECREASE c. So … increase solute = decrease vapor pressure ***KNOW HOW TO***** Convert grams, molarity, molality, mols, % by weight, density, mol fraction etc. into each other, respectively o For example if a freezing point depression question gives you 25% by weight of the solute you have to be able to assume 100 grams of solution so that means you have 25 grams of solute and 100-25= 75 grams of solvent. So you can then convert grams of solvent to kilograms. Convert grams of solute to mols. Divide mols of solute by kilograms of solvent and calculate the molality. Thus being able to plug the molality in and solving the equation. Chapter 14 Reaction Rates, Rate Law Expressions, Method of Initial Rates **be sure to pay attention to the wording of the problems to determine whether or not an answer should be reported as positive or negative …. For example the word “removal” would already indicate a loss of whatever it is you are looking for so report a positive answer Rate of Disappearance is equivalent to the change in concentration of whatever reactant/product you are looking for divided by the change in time Increased concentration of reactants = increased rate= increased particles = more opportunities for collisions to occur Effective collision is the energy of the particle to overcome energy barrier AND the correct orientation for the reaction to occur Rate is impacted by… Concentration of reactants Temperature Physical state of the reactants Presence of a catalyst Pressure To determine the order of a given reactant …. Given a table of data. Pick one set of data for the reactant you are looking for that changes! At the same time pick the set of data that corresponds to the other reactants that STAYS THE SAME Ratio the rates for each set of data and set it equal to the ratio of the rate constants [with filled in values chosen from first two steps] for each set of data. The constant group will cancel out and you will be left with a number = a number raised to a coefficient of x, y, or z. In order to solve for the coefficient take the natural log (ln) of both sides and divide appropriately to solve for your missing variable When dealing with Rate law and Rate Law Constants (k) be sure that k is in the appropriate units associated with the order of the reaction you are working with! Integrated Rate Equations ****METHOD OF INITIAL RATES PROBLEM WILL BE ON THE TEST! Integrated rate law problems are only used when you have one reactant that is known!!! *if a problem states “rate of consumption” report your answer as positive! When dealing with integrated rate law your TIME units MUST match the time units given in your RATE CONSTANT K o I personally recommend changing any times BEFORE computing an answer … I feel like it is easier that way and you are less likely to calculate the wrong answer Also know that each integrated rate law can be plotted to form a line …. ! There may very well be a question on the test that gives you a graph and asks what order the reaction is … so you must know what slow corresponds to what order integrated rate law equation *** If given a problem that asks for the concentration of a reactant/product with NO INITIAL CONCENTRATION …. DO NOT USE INTEGRATED RATE LAW EQUATIONS Set up a molar ratio using the concentration of the reactant that DID have an initial concentration. (This value will be the value you calculated using the integrated rate law equation). So if the concentration of A after 2 seconds in 2a B equals 1M then you would divide 1M A by 2 mols A for every 1 mol of C Collision Theory If temperature increases the higher the number of particles that have enough energy to undergo chemical reaction will increase = an increase in reaction rate o A larger fraction of molecules that have the energy to collide and cause a reaction A transition state is the state of a reactant in the middle of being converted from a reactant to a product or vice versa HIGH ENERGY For a reaction to occur the molecules must have the PROPER MOLECULAR ORIENTATION o For example cannot bond to a hydrogen that is already bonded; usually will have to bond somewhere on central atom (not always the case though) A catalyst creates a DIFFERENT PATHWAY for the reaction to occur; changes the mechanism of the reaction speeds up reaction *the slow reaction is the RATE DETERMINING reaction Reaction Mechanisms A products = unimolecular rate = k[A] A + B product = bimolecular rate = k[A][B] A+A product = bimolecular rate = k[A]^2 2A + B product = termolecular rate = k[A]^2[B] *elementary steps tell you how to get from A B *each step in a mechanism is an elementary step Chapter 15 Equilibrium Rates of forward and reverse reactions are equal when in equilibrium (RATES are equal NOT amounts of reactants vs. products!) Be careful with heterogeneous reactions (involve solids and liquids and gases) liquids and solids will NOT show up in the rate constant for an equation involving a gaseous reactant/product Equilibrium constants are a function of temperature and activation energy If Kc is < 1 the reaction is reactant favored If Kc > 1 the reaction is product favored Solve for Qc to determine which direction the reaction is going in Qc < Kc reaction will go forward Qc > Kc reaction will go reverse Set up ICE charts to solve for X then in turn solve for the concentrations If a reaction is going reverse the products concentration will be equal to –x and the reactants will be equal to +x If a reaction is going forward the reactants concentration will be equal to –x and the reactants will be equal to +x If you increase partial pressure it will stress the equilibrium and the reaction will move to the left o When you change pressure you change volume which changes the molar concentration If you have equal mols of product gas and reactant gas the pressure wont change If you are not given concentrations but pressures then set up an ICE chart in terms of partial pressure No initial product means the reaction will definitely move forward Pressure equilibrium will be when the time and pressure at which pressure stars being constant Equations are attached hand written because IDK how to do all that nonsense on the computer (: HOPE THIS HELPS ATLEAST A LITTLE BIT WE GOT THISSSSS !!!!
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