CHE 131: General Chemistry, Notes for Exam 2
CHE 131: General Chemistry, Notes for Exam 2 CHE 131
Stony Brook U
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This 5 page Study Guide was uploaded by Robert_Smith on Sunday March 20, 2016. The Study Guide belongs to CHE 131 at Stony Brook University taught by Roy Lacey in Winter 2016. Since its upload, it has received 25 views. For similar materials see General Chemistry IB in Chemistry at Stony Brook University.
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Date Created: 03/20/16
03/20/2016 CHE 131: General Chemistry Exam 2 Study Guide ____________________________________________________________________________ __ Limiting Reactants Limiting Reactan the reactant that limits how long the reaction takes It will always be used up by the end of the reaction You can check for the limiting reactant by testing which reactant produces the least amount of a certain product, using their molar ratios from a balanced equation Percent Yield the amount of product created in real life divided by how much theoretically should have formed ____________________________________________________________________________ __ Solutions solutions a homogeneous mixture of two or more substances Can be a gas, solid, or liquid A solvent exists in greater quantity and dissolves a smaller amolute s Ionic substances dissolve into their ions; molecular substances do not disassociate Concentration mount solute / amount solution Molarit a measure of concentration, (moles solute) / (liters solution) Unit is M Dilution involves lowering the molarity of a solution by adding stock solution to a solute MdiluVdil= Mconcentraeconcentrated ____________________________________________________________________________ __ Electrolytes, AcidBased Reactions, & Precipitation Solubility soluble substancewill dissolve in a solution and not recipitat(a solid formed by the combination of two insoluble ions) Soluble cations: alkali metals, ammonia Soluble anions: nitrate, acetate, halides, sulfates Insolubilit insoluble substancewill form a precipitate in solutions Soluble compounds: hydroxides, sulfides, carbonates, phosphates 03/20/2016 Electrolytes a solute that makes ions in a solution These ions harge carriers)can run an electric current through the solution Nonelectrolytes does not ionize or run a current (e.g. sugar) Strong electrolytes breaks down almost completely into ions, conducts electricity well Weak electrolytes only partially dissociate into ions, don’t conduct electricity well The strength of an electrolyte isn’t related to its solubility Ionic Equation an equation that shows the ions formed by the reactants and the products A Net Ionic Equationdoes not includpectator ions (ions that don’t change during the reaction and are the same on either side of the equation) ____________________________________________________________ AcidBase Reactions, Stoichiometry, & Titrations Amphiprotic substances that accept or donate protons (e.g. water) Neutralization reaction an acid and base combine to create a salt and water Equivalence point point in a redox titration when the number of electrons lost by the oxidized substance equals the number gained by the reduced species Titration when one adds an unknown substance to a known solution until the equivalence point has been reached (usually marked by a change in the solution’s color One usually does this to try to find the concentration of the unknown solution using thetitran(the concentration of the known solution) ____________________________________________________________ Redox Equations Redox Reaction (or OxidationReduction Reaction) involve the transfer of electrons The electron transfer is marked by the change inoxidation numbers ( the charge of the ion formed by part of the substance) Oxidation numbers are 0 for neutral atoms, usually +1 for H except when it forms hydrides with metals (then it is 1), it is usually 2 for O Oxidation increases a substance’s oxidation number (it becomes more positive as it loses electrons) Reduction decreases a substance’s oxidation number (it becomes more negative as it gains electrons) 03/20/2016 Oxidizing agent does oxidation, is reduced Reducing agent does reduction, is oxidized Balancing Redox Equations Split equation into halfreactions of oxidation and reduction Balance all elements, using water to balance O and H+ (for acidic solutions) or OH (for basic solutions) to balance H Balance charge with electrons ____________________________________________________________ Gasses, Pressures, & Gas Laws Ideal Gas Law PV = nRT R is the gas constant, which is given during exams T must always be measured in Kelvins, not celsius. This is true for all of the following gas laws P is pressure in atm, V is volume in liters, and n is the number of moles Boyle’s Law V = k/P k is a constant Charles’ Law V = bT b is a constant Avogadro’s Law V = a n a is a constant, and n is the number of moles Pressure P = F / A Pressure equals force per unit area Units: 1 atm = 760 mmHg = 760 torr = 101.325 kPa A manometer measures pressures of various gases Standard temperature and pressure (STP) at STP, T = 273 K and P = 1 atm At STP, l mole of gas takes up 22.4 L Density (PM) / (RT) M is the molar mass of the gas R is the gas constant, which is given during exams ____________________________________________________________ Dalton’s Law, Kinetic Molecular Theory, & Real Gases 03/20/2016 Dalton’s Law is a way to calculartial pressur(pressure exerted by one gas in a mixture) P =(niRT)/V Ptot = P1 +P2 + .Pn =ntot((RT)/V) Mole Fraction the proportion of the mixture that the gas makes up na a χ =a na+b +..n n ntotal Pa =χaP otal Kinetic Molecular theory a model that explains gas behavior Pressure is the impulse per collusion times the frequency of collisions with the walls of the container PV = Nm u2 u = 3RT M 2 M is the molar masu. s the mean speed of all the molecules squared. Average Kinetic Energy (Temperature) KEavg= (3/2)RT Diffusion the mixing of gases, happens more quickly for light molecules Effusion the rate at which gas molecules pass through a small hole in a chamber Real vs. Ideal Gaseseal gases don’t acct ideally at high pressures because of intermolecular forces and the finite volume of gas molecules Adjusted Ideal Gas Law 2 (Pobs+ a(n/v) (Vnb) = nRT ____________________________________________________________ Forms of Energy & Enthalpy Energy is stored in chemical bonds, is used and released during chemical equations Potential energ energy based on position Chemical Energy stored in bonds Kinetic Energy k = (1/2) m v , m is mass and v is velocity Work = force times distance Units 1 J = (1 kg m )/s1 cal=4.184 J 1 Cal = 1 cal System ncludes everything involved in reactions, buurroundings 03/20/2016 Open system allows mass and temperature changes Closed system a llows temperature changes Isolated system doesn’t allow any changes State function measures only the difference between the starting and ending state, the path between the two states does not matter Equations ΔE = q + w ΔE is the energy change, q is heat, w is work done on system W = P ΔV ΔP is the volume change, w is work, P is pressure ΔH = ΔE V ΔH is the enthalpy change ____________________________________________________________ Calorimetry Exothermic heat is released to surroundings Endothermic heat is absorbed from surroundings Enthalpy H = E + PV ΔH = ΔE + PΔV Calorimeter a device used to measure heat exchanges during reactions Specific heat capacity the heat required to raise the temperature of one gram of a substance by 1 degree Celsius at constant pressure
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