Chemistry 1220 Exam 1 study guide
Chemistry 1220 Exam 1 study guide CHEM 1220
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This 11 page Study Guide was uploaded by Sean Bhatnagar on Monday January 25, 2016. The Study Guide belongs to CHEM 1220 at Ohio State University taught by Dr. Fus in Spring 2016. Since its upload, it has received 143 views. For similar materials see General Chemistry 1220 in Chemistry at Ohio State University.
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Date Created: 01/25/16
Chemistry Study guide 1 chapters 11 13 and 14 111 Intermolecular forces in liquids and solids are much stronger than those in gases Assumes both volume and shape of its container Expands to ll its container Is compressible Flows readily Diffusion within a gas occurs rapidly Liguid Assumes shape of portion of container it occupies Does not expand to ll its container Is virtually incompressible Flows readily Diffusion within a liquid occurs slowly w Retains own shape and volume Does not expand to ll its container Is virtually incompressible Does not ow Diffusion within a solid occurs extremely slowly 112 Intermolecular forces are weaker than intramolecular forces 0 3 types of intramolecular forces ionic metallic and covalent bonds 0 Boiling points go up as intermolecular forces go up Melting points go up as intermolecular forces go up 0 3 types of intermolecular forces dispersion forces dipoledipole and hydrogen bonding collectively called the quotvan der Waals forcesquot All intermolecular forces are electrostatic involving positive and negative species like ionic bonds Interactions get stronger the as the magnitude of the charges increases and weaker as the distance between charges increases Dispersion forces are based on instantaneous dipole moments also called quotLondon dispersion forcesquot Instantaneous dipole moments are based on electrons moving in the electron cloud At some point in time the distribution of electrons on each side of the nucleus may be lopsided creating a small dispersion charge Polarizability the ease at which the charge distribution is distorted the quotsquishiness of the electron cloudquot 11 Polarizability increases as the number of electrons increases So in general the dispersion forces increase as the size of the molecule increases The shape of the molecule also changes the magnitude of the dispersion forces The permanent presence of dipole moments are called quotdipoledipole forcesquot based on if a molecule is polar or not draw a lewis structure DipoleDipole forces are stronger than dispersion forces Hydrogen Bonds gt DipoleDipole Bonds gt Dispersion Forces Hydrogen bonding occurs between hydrogen and uorineoxygennitrogen Hydrogen bonds are the strongest because there is only one electron so the dipole is very very strong Iondipole forces occur between an ion and a polar molecule When the molecular weights differ greatly the attractive forces are generally stronger in the substance with the higher weight 3 Viscosity resistance of a liquid to flow molasses Viscosity can be measured by the time it takes a liquid to ow through a thin vertical tube or at which a steel ball falls through liquid Viscosity decreases at higher temperatures Surface tension the energy required to increase the surface area of a liquid by a unit amount Surface area is based on the net interior pull of molecules making the liquid at the surface pack closely together Cohesive forces intermolecular forces that bind similar molecules to one another Adhesive forces intermolecular forces that bind molecules to a surface Capillary action when liquid rises up a very narrow tube based on adhesive forces to the tube wall and surface area reducing surface area pulling the liquid up the tube used for nutrients in plants 4 Phase changes changes of state Phase changes are accompanied by a change of energy in the system Fusion and melting are the same quotheat of fusionquot is in kJmol Sublimation solid to gas Vaporization liquid to gas Temperature remains constant until the END of the phase change Heating curves look like stairs the at parts are the phase changes and the inclines are the heating portions Heating curve graph of temperature vs heat added Critical point the highest temperature at which a distinct liquid phase can form 11 11 11 Critical pressure pressure required to bring about liquefaction at this critical temperature Supercritical uid when temperature exceeds the critical temperature and pressure exceeds the critical pressure the gas and liquid phases are indistinguishable 5 As molecules vaporize from liquid to gas the gas exerts a pressure on the closed container Vapor pressure pressure of the vapor on the container once it has reached a constant value when the LZGGZL transitions are in equilibrium Volatile liquids that evaporate readily Substances with high vapor pressures means the equilibrium has higher gas content because equilibrium only refers to the equality in RATES Temperature increase will increase vapor pressure because the increased kinetic energy given to molecules allows more of them to break out of the liquid phase Normal boiling point boiling point of a liquid at 1atm Boiling point point at which the vapor pressure is equal to that of the external pressure Clausiusclapeyron equation describes the relationship of vapor pressure and temperature 6 Phase diagram three branched chart used to describe the equilibrium conditions between states think SLG in a clockwise fashion starting with the leftmost state Vapor pressure curve the curve between gas and liquid on the phase diagram ends at the critical point beyond which is the supercritical uid Sublimation curve curve between the solid and gas phase Melting curve curve between the liquid and solid phase usually slopes towards the right as pressure increases because in most cases solid is more dense than liquid Normal melting point melting point at 1atm Triple point the intersection of the vaporpressure sublimation and melting curves Melting curve for water slants backwards because of the rare liquid is denser than solid characteristic for water 7 Liquid crystal the viscous milky state of some organic compounds Liquid phase molecules arranged randomly think scattered rattlesnake egg magnets REMs Nematic liquid crystalline phase long axes of molecules aligned but not aligned at ends think REMs all standing up but at different heights Smectic A liquid crystalline phase Molecules aligned in layers long axes of molecules perpendicular t layer planes remember perpendicular Smectic C liquid crystalline phase molecules aligned in layers long axes of molecules inclined with respect to layer planes think slightly skewed but similar to smectic A Certain liquid crystals stack better due to benzene rings Cholisteric liquic crystal the molecules pack into layers the long axis of each molecule is oriented parallel to its neighbors within the same layer think single slices of the other phases stacked horizontally atop one another Cholisteric liquid crystals produce unusual color patterns with visible light used to monitor temperature changes when conventional methods are unfeasible Chapter 13 Properties of Solutions 131 Solutions are formed when one substance disperses uniformly throughout another The mixing of gases is a spontaneous process associated with an entropy increase Gases spontaneously mix unless restrained by their containers Solutions made from solutes of solid or liquid state may or may not mix based on the intermolecular forces think NaCl and H20 Dispersion forces dominate in nonpolar NP nonpolar solutions Iondipole forces dominate in ionic substances in water Solutesolute interactions between solute particles must overcome in order to disperse the solute particles through the solvent Solventsolvent interactions between solvent particles must be overcome to make room for the solute particles in the solvent Solventsolute interactions between solvent and solute particles occur as the particles mix Solvation when solute molecules are surrounded by solvent molecules Hydration solvation with water as the solvent AHsoln AHsolute AHsolvent AHmix Separation of solvent and solute molecules requires energy so the enthalpy is positive then it drops down largely when mixed as this releases energy The difference between the mixed energy released and the energy required to break the bonds is the AHsoln This chart of the aforementioned points is the Hess s Law one lonic solutes do not dissolve in nonpolar solvents Polar liquid solutes water will not dissolve in a nonpolar liquid solvent octane Chemical reactions cannot be recovered when dehydrated unlike physical reactions salt in water when dehydrated will recover the salt 132 Crystallization as more particles dissolve there is a higher chance of them colliding with the surface and reattaching to the surface of the original solid this is the opposite of the solution process Equilibrium is reached when the rate of crystallization and the rate of solution are equal Saturated a solution in equilibrium with undissolved solute additional solute will not dissolve Solubility the amount of solute needed to form a saturated solution in a given quantity of solvent Unsaturated when less solute is dissolved than the amount needed to form a saturated solution Supersaturated when under suitable conditions more solute is dissolved than that of a saturated solution Usually heat is used to make a solution supersaturated when the solution is cooled down particles will fall out of solution and crystallize because a supersaturated solution is considered unstable However for crystallization to occur the particles must align themselves to properly form crystals 133 The stronger the attractions between the solute and the solvent the greater the solubility of solute in that solvent POLAR DISSOLVES POLAR due to favorable dipoledipole interactions Miscible pairs of liquids that mix in all proportions acetone and water lmmiscible pairs of liquids that do not dissolve one another gasoline and water gasoline is NP and water is P Hydrocarbons molecules just containing C and H atoms are NP NONPOLAR DISSOLVES NONPOLAR Alcohols Organic compounds with a framework of hydrocarbons with a polar OH group attached these groups are able to form hydrogen bonds For alcohols as the number of carbon atoms increases the OH group becomes an ever smaller part of the molecule making it act more nonpolar decreasing its solubility in water and increasing its solubility in NP solvents To increase its solubility the molecules should increase OH groups why glucose which has 5 OH groups is very soluble in water Finally LIKE DISSOLVES LIKE The solubility of any gas is increased as the partial pressure of the gas above the solvent increases pressure increases increase solubility Henry s law Sg kPg relates partial pressure of gases and solubility of the gases Solubility of solid solutes in water tends to increase as temperature increases as seen by solubility curves Solubility of gaseous solutes in water decreases with increasing temperature think of when you warm a glass of cold tap water bubbles rise because the air dissolved comes out of solution Thermal pollution warm water is less dense than cold water so it sits at the surface As it is warmer less oxygen can dissolve in it which means less oxygen can get to deeper water and life can die 134 Mass percentage mass of component in solutiontota mass of solution X 100 Very dilute solutions are measured in quotparts per million ppmquot and quotparts per billion 9quot Ppm mass of componenttota mass X 106 Ppb is the same as ppm except with 109 Mole fraction of component moles of componenttota moles of all components X is typically used as a symbol for mole fraction Molarity M moles of soluteliters of soln Molality m moles of solutekg of solvent KNOW HOW TO CONVERT BETWEEN CONCENTRATION UNITS 135 Colligative properties depend on the quantity concentration but not the identity of solute particles Examples of colligative properties freezingpoint lowering boilingpoint raising vaporpressure lowering and osmotic pressure Nonvolatile a substance with no measurable vapor pressure Adding a nonvolatile solute to a volatile solvent decreases the overall vapor pressure The vapor pressure of a volatile solvent above a solution containing a nonvolatile solute is proportional to the solvent39s concentration in the solution RaOUIt39S LaW Psoln XsolventPosolvent AP XsolutePosolvent ldeal solution one that oberys Raoult39s Law there are many cases where the solution is not ideal Addition of a nonvolatile solute brings down the vapor pressure which brings down the vaporpressure curve LG curve making a higher temperature for the normal boiling point Hence increasing the boiling point Change in boiling point is directly related to molality m ATb Kbm Kb quotmolal boilingpointelevation constantquot Molality is based on the TOTAL moles of solute particles 1m of NaCl is 2m 1m Na 1m C So consider whether the solute is an electrolyte or nonelectrolyte when calculating boilingpoint elevation Based on the previous note of how the vaporpressure curve moves down the triple point is moved to the left thus decreasing the normal freezing point ATf Kfm Osmosis the net movement of solvent toward the solution of higher solute concentration as if the solutions were driven to attain equal concentrations Osmotic Pressure OP oberys a law similar to the ideal gas law OPVnRT when the V is divided nV is M so OP MRT Cell in hypertonic environment higher solute concentration outside causes solvent to leave the cell the cell will shrivel this is called crenation Cell in a hypotonic environment higher solute concentration inside causes solvent to enter the cell the cell will swell or even rupture this is called hemolysis lsotonic solution one that matches the concentration of the cell preventing crenation and hemolysis 136 Particles 5nm to 1000nm are considered quotcolloidal particlesquot they are small enough to remain suspended in solution but large enough to be seen or have an effect on the aesthetic Colloids solutions containing colloidal particles or dealing with colloidal dispersions Tyndall effect the scattering of light by a colloid Examples of colloids fog smoke aerosol whipped cream foam milk emulsion paint sol marshmallow solid foam butter solid emulsion ruby glass solid sol Most important colloids are those where the solvent is water they are either hydrophilic water loving or hydrophobic water fearing Typically a colloid will have hydrophobic groups on the interior of the molecule with hydrophilic polar groups on the surface interacting with the water enzymes antibodies Adsorption adhering to a surface ions adsorb to hydrophobic molecules to stabilize them To remove colloidal particles coagulation must be used Heating a colloidal dispersion or adding an electrolyte to a dispersion brings about coagulation increasing the size of these colloidal particles and allows them to be ltered out In dialysis a semipermeable membrane is used to allow the passage of ions and prevent the passage of colloidal particles Chapter 14 Chemical Kinetics Kinetics is based on the rates at which reactions occur called quotreaction ratesquot Reaction mechanism stepbystep molecularlevel view of the pathway from reactants to prducts 141 Factors that affect reaction rates are as follows Physical state of the reactants for example reactions involving solids will occur faster if the solid has greater surface area hence why many medicines are in the form of a powder Reactant concentrations many reactions will occur faster if the concentrations of one or more reactants is greater steel wool bursting into ames in pure oxygen but burning slowly in air which is only 20 02 Reaction temperature reaction rates generally increase as the temperature increases as T goes up KE goes up increasing collisions increasing the likelihood of reactions occurring The presence of a catalyst catalysts speed up reactions Catalyst agents that increase reaction rates without themselves being used UP On a molecular level reactions are based on collisions For a collision to lead to a reaction however it must be with enough energy to break the bonds and the right orientation to form the new bonds 142 Reaction rate change in concentration of the reactants or products per unit of time usually molarity per second Ms By convention rates are expressed as positive quantities so include a H when calculating the rate of disappearance of a reactant It is typical for rates to decrease as a reaction proceeds because the concentration of reactants decreases Instantaneous rate rate at a particular instant during the reaction approximated using tangent lines like in calculus To nd a reaction rate that is balanced on stoichiometry multiply the instantaneous rate by one over the coef cient You do not need to do this to nd the rate of a certain reactant or product 143 Rate law kAB K is referred to as the quotrate constantquot K must have the units that cancel out the individual reactants rates until the nal units are Ms Reaction order the exponents on the reactants in the rate law Overall reaction order the sum of the exponents Second order increasing the concentration by two quadruples the rate exponent of 2 Zero order takes the reactant out of the rate law exponent of zero reactant s concentration has zero impact on the rate Rate laws can only be determined experimentally there is no correlation between exponents and reaction orders although it may seem as if there is Most reaction orders are 0 1 or 2 but instances occur where the reaction order is fractional K of 109 or greater means a fast reaction k of 10 or less indicates a slow reaction Rate of a reaction depends on the concentration however the rate constant does NOT 144 Relating a rate law to time involves integration Firstorder reaction nAt nAo kt Secondorder reaction 1At kt 1Ao To nd the order without rate data plot nA and 1A vs time and see which is linear Zeroorder reaction At kt Ao Halflife tm the time required for the concentration of a reactant to reach half of its initial value To solve for halflife given a rate constant simply plug in 12 the initial concentration for At In a rstorder reaction the concentration of the reactant decreases by 12 in each series of regularly spaced time intervals each interval equal to t12 In secondorder and other reactions the halflife depends on the concentrations and therefore changes as the reaction progresses 145 As temperature increases so does the reaction rate this is due to the rate constant being dependent on temperature Collision model based on kineticmolecular theory this model accounts for the effects of both reactant concentrations and temperature on the rate of the reaction Collision model says as concentration increases the likelihood of collisions increases increasing reaction rates Also as temperature increases as does kinetic energy increasing the force and frequency of collisions Molecules must be oriented in a certain way during a collision for the reaction to take place Activation energy the minimum energy required to initiate a chemical reaction Activated complextransition state the arrangement of atoms shown at the top of a reaction39s energy pro le at the highest activation energy RATES ARE DEPENDENT ON ACTIVATION ENERGY At higher temperatures a larger fraction of molecules have suf cient kinetic energy to overcome the activation energy and cause a reaction f equot EaRT where R is 8314 JmolK Arrhenius equation relates the temperature and activation energy to the reaction rate Arrhenius k Aequot EaRT k is the rate constant Ea is the activation energy R is the gas constant previously mentioned T is the absolute temperature A is the frequency factor 146 Reaction mechanism steps by which a reaction occurs Elementary reaction reactions that occur in a single event of a single step Molecularity the number of molecules that participate as reactants in an elementary reaction Unimolecular moecuarity of 1 Bimolecular and termoecuar are selfexplanatory using the above buet Termolecular reactions are very rare in comparison to uni and bi four or more is so rare that they are never proposed as part of a reaction mechanism Multistep mechanism consists of a sequence of elementary reactions that result in the balanced chemical equation Intermediate a molecule that is created in one of the steps and consumed in the next a reactant and product that is not in the nal balanced chemical equa on Intermediates can be identi ed as the trough between two transition states in an energy pro le of a reaction Rate laws can only not be determined experimentally if the reaction is elementary then it is based on the moecuarity Ratedetermining step step in the mechanism that is the slowest has the highest activation energy Whenever a fast step precedes a slow one we can solve for the concentration of an intermediate by assuming that an equilibrium is established in the fast step Manipulating the fast steps rate laws and solving for the intermediate allows one to create a rate law for the overall reaction based on the slow step that does not involve the intermediate 147 Catalyst a substance that changes the speed of a chemical reaction without undergoing a permanent chemical change itself Homogenous catalyst a catalyst that is present in the same phase as the reactants in a reaction mixture A catalyst is present at the start and end of a reaction while an intermediate is created and consumed during the reaction A catalyst lowers the overall activation energy of a reaction possibly by offering a different mechanism for the reaction Heterogenous catalyst a catalyst that exists in a phase different from the phase of reactant molecules usually as a solid in contact with either gaseous reactants or with reactants in a liquid solution Heterogenous catalysts are usually metals or metal oxides and are given very large surface areas because the rst step in catalysis is the adsorption of reactants to the surface of the catalyst Enzyme a biological catalyst Most enzymes are large protein molecules that are very selective in the reactions they catalyze sometimes an enzyme will only operate in only one reaction Active site where the enzyme catalysis takes place Substrate the substance that reacts at the active site Lockandkey model the substrate acts as the key and the active site as the lock Enzymesubstrate complex the combination state of the substrate and the active site Enzyme inhibitors when anything other than the necessary substrate attaches to the active site it destroys the activity of the enzyme nerve poison
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