Chem 162 Final Exam Questions and Answers Latest Updated 2024/2025 (Graded A+)

Chemistry definition correct answers Study of structure, properties, transformations of matter Matter correct answers Anything that has mass + takes up space Phases: solid, liquid, gas Condensed phases = solids + liquids Intermolecular Forces (IMF) correct answers = Interactions between molecules/atoms/ions Solution correct answers = Homogenous mixtures of 2+ pure substances In a solution, the solute is dispersed uniformly throughout the solvent - Solute = compound(s) in lesser amount - Solvent = compound in greater amount E.g. air Ability of substances to form solutions depends on ... ? correct answers 1) Natural tendency toward mixing (always favorable): - Entropy = measure of energy randomization/energy dispersal in a system - All things in nature want to be as spread out/disordered as possible (AKA increase their entropy) - Solution formed = entropy of system is increased! 2) Intermolecular Forces (depends on solute-solvent interactions): - Strength of IMF: attractive intermolecular forces are another one of the big driving forces contributing to solution formation between solute/solvent molecules. Covalent VS Ionic Compounds correct answers Covalent = generally more soluble in nonpolar solvents, b/w 2 nonmetallic atoms Ionic = generally more soluble in polar solvents, b/w 2 atoms with opposite charge Solute-Solvent interactions correct answers Soluble compound = can mix homogeneously in all proportions with another compounds Insoluble compound = cannot mix homogeneously in all proportions with another compound Miscible liquids = mix in all proportions with another liquid Immiscible liquids = do not mix in one another Chem 162 Final Exam Questions and Answers Latest Updated 2024/2025 (Graded A+) Range of solubility for all compounds: stronger the solute-solvent interaction, greater solubility of a solute in that solvent *** In order for a solute-solvent interaction to be favorable (soluble with each other), both must have SIMILAR POLARITY! "LIKE DISSOLVES LIKE" Solute-Solvent Combinations correct answers Soluble: - Polar + polar: water, sugar - Ionic + polar: "Hydration Shells" = solvent interface of any compound that consists of the solute. - Non-polar + non-polar: octane Insoluble: Non-polar + polar Ionic + non-polar Non-Polar Gases in Water correct answers London dispersion force = weakest IMF, temporary attractive force when electrons in 2 adjacent atoms occupy positions that make the atoms form temporary dipoles. E.g. N2, O2, Ar, Kr in water *** Larger gas = more soluble it will be in water Solubility of non-polar gases is VERY low, but solubility will increase with increasing London dispersion forces! Solute-solute interactions (Forming a Solution) correct answers Must be OVERCOME to DISPERSE PARTICLES when making a solution These "interactions" could be IMF in covalent compounds, Coulombic attractions in ionic compounds, metallic bonding in metals, etc. Solvent-solvent interactions correct answers Must be OVERCOME to MAKE ROOM for the solute (same types of interactions as above) Solvent-solute interactions correct answers Must be LARGE ENOUGH to COMPENSATE FOR THE ENERGY that must be put into breaking solute-solute + solvent-solvent interactions (same types of interactions as above) Must be GREATER THAN solvent-solvent + solute-solute interactions to form solution, because increasing entropy/creating more favorable IMF = solvent-solvent + solute-solute interactions, solution still forms because entropy is still increasing solvent-solute solvent-solvent, solute-solute: solution may or may not form, depending on relative disparity (solution wants to form to increase entropy, but it may/may not overcome breaking already-very-favorable interactions) Relative energies of solution formation correct answers delta H (solution) = delta H (solute) + delta H (solvent) + delta H (mixture) delta H = heat energy "energy" for a reaction to occur, delta H (mixture) must be close in magnitude to the sum of delta H (solute) + delta H (solvent) - AKA solvent-solute = solute-solute and solvent-solvent *** Energetically favorable solution formation: decrease in enthalpy (thermodynamic quantity) AND/OR increase in entropy (randomness) Aqueous solution correct answers = Solution where the solvent is liquid water Most common type (Remember: solutions can be made with any phases of matter!) Solubility of aqueous solutions correct answers Solubility = MAXIMUM amount of solute that can dissolve in a given amount of solvent at a given temperature Saturated solutions = have maximum amount of solute dissolved in the solvent to which NO MORE SOLVENT can be dissolved at a given temperature Unsaturated solutions = any amount of solute less than the maximum amount dissolved in solution (at a given temperature). Supersaturated solutions = have more solute dissolved than a saturated solution (normally possible) at a certain temperature Supersaturation correct answers Usually made by increasing the solvent's temperature, making a saturated solution at the higher temperature, then cooling the solution to a lower temperature very carefully These solutions are unstable - crystallization can usually be stimulated by adding a "seed crystal" or scratching the side of the flask Dissolving + Crystallization correct answers Dissolving = solutes into solvents Crystallization = opposing process of dissolving, occurs when solute particles join back together Rate of opposing processes is equal = additional solute will not dissolve unless some solute crystallizes from solution -- SATURATED SOLUTION If we have not yet reached the amount that will result in crystallization -- UNSATURATED SOLUTION Temperature effect on solubility correct answers Generally, the solubility of SOLIDS into liquids INCREASES with INCREASING TEMP * Ce2(SO4)3 = exception Examples: - Making tea - Making rock candy Solubility of GASES into liquids DECREASES with INCREASING TEMP Examples: - Flattening of soda left out on a hot day - Thermal pollution Pressure effect on solubility correct answers Solubility of GASES into liquids INCREASES with INCREASING PRESSURE * Solubility of solids into liquids is not substantially effected by pressure! Examples: - Pop of soda when opening can - Scuba diving accidents when coming up too fast Why do bubbles form on the inside wall of a cooking pot when water is heated on the stove, even though the water temperature is well below the boiling point of water? correct answers Dissolved gases are less soluble in solution as temperature increases Henry's Law correct answers = Quantifying the phenomenon that the solubility of gases into liquids INCREASES with increasing pressure Expressing Solution Concentration correct answers Qualitatively, we can say a solution is "dilute" in a certain solute or "concentrated" in a certain solute However, we would like to quantify the amount of solutes in solutions - there are many different ways to quantify solution concentration! Main way: Molarity (M) = moles solute/Liters solution Molality (m) = moles solute/kg solvent Mass Percent correct answers Mass % = mass solute (g)/mass solution (g) x 100 = Wt/Wt% (Wt%) ppm and ppb correct answers Sometimes, solutions are very dilute in solute concentration. So, we tend to use "parts per million (ppm)" or "parts per billion (ppb)" ppm = mass solute (g)/mass solution (g) x 10^6 ppb = mass solute (g)/mass solution (g) x 10^9 Volume Percent correct answers Volume % = mL or L of solute/mL or L of solution x 100 = Vol/Vol % ppm = mL of solute/mL of solution x 10^6 ppb = mL of solute/mL of solution x 10^9 Consequences of solutions on physical properties correct answers Colligative properties = depend on the NUMBER OF PARTICLES present in a solution, NOT on the type of particles present Examples: - Vapor pressure lowering - Freezing Point Depression - Boiling Point Elevation - Osmosis Vapor pressure lowering - Colligative Properties correct answers When a solution is made with a NON-VOLATILE solute (not easily evaporative), the vapor pressure of the solution is lower than the vapor pressure of the pure solvent Raoult's Law for Non-Volatile Solutes correct answers P(solution) = X(solvent) x P(solvent) For 2+ volatile (evaporative) components in a solution, Raoult's Law also states that the partial vapor pressure of each volatile component of an ideal mixture of liquids = vapor pressure of pure component x mole fraction in the mixture Freezing Point Depression - Colligative Properties correct answers Generally, adding a solute to a solvent LOWERS the solvent's freezing point delta T(f) = i x m x K(f) New FP of solution = T(original solvent) - T(new soln) i = van't Hoff factor m = molality (mols solute/kg solvent) K(f) = Freezing Point depression constant for the solvent E.g. in the winter, the wood frog floods its cells with sucrose to prevent its vital organs from fully freezing. Van't Hoff Factor (i) correct answers = Term used in various colligative property equations in order to account for IONIC COMPOUNDS breaking up into multiple particles in solution Boiling Point Elevation - Colligative Properties correct answers Generally, adding a solute to a solvent INCREASES the solvent's boiling point delta T(b) = i x m x K(b) delta T(b) = T(new solution) - T(original solvent) Osmosis correct answers = flow of solvent from a solution of lower solute concentration to a solution of higher solute concentration, through a semipermeable membrane * Remember: nature wants to be as spread out + random as possible (entropy)! Osmosis creates pressure buildup on the side the solvent is traveling TOWARDS Process of osmosis is 1 great reason why you should not drink saltwater (or anything too salty) to hydrate yourself! (Seawater in intestinal tract = concentrated solution, interior of body cells = dilute solution) Osmotic Pressure correct answers pi = iMRT R = 0.0821 L x atm/mol x K Biological applications of osmosis correct answers Red blood cells (RBCs) have semipermeable membranes Like the small intestine + other types of cells in the body, red blood cells are at the mercy of osmosis - Shriveled red blood cells = crenation, HYPERTONIC solution, concentration inside the cell concentration outside the cell, so the cell shrivels! - Swollen red blood cells = hemolysis, HYPOTONIC solution, concentration inside the cell concentration outside the cell, so the cell bursts! Colloids correct answers = Suspensions of particles larger than individual ions/molecules/solid particles, but too small to be settled out by gravity (5-1000 nm) e.g. fog, smoke (ash in air), whipped cream (air bubbles in butterfat), milk, opal *** DEFINING CHARACTERISTIC: TYNDALL EFFECT!!! E.g. Soapy water: - Typical soap molecule structure has nonpolar tail + ionic head - Soap molecules come together to form 3D spherical structures (micelles) in order to interact with water as little as possible: nonpolar tails on inside, ionic heads on outside (water on exterior) - Micelles act as emulsifiers because they help in allowing oils/fats to be "washed away" in water Tyndall Effect correct answers = Phenomenon of colloidal suspensions able to scatter rays of light (solutions cannot do this!) Other examples: - Laser show - Headlights on a foggy night Chemical Kinetics correct answers = area of chemistry concerned with the rates (speeds) of chemical reactions Kinetics also offers insight into the energy required for a reaction to begin (activation energy) + reaction mechanisms (step-by-step way bonds are broken + reformed in chemical reactions) Reaction rate correct answers = rate of a chemical reaction measured in how much the reactant's concentration decreases (reactants used up) OR product concentration increases (produces products) in a given time period Relative reaction rates can be fast or slow - we want to study how fast a reaction proceeds Average rate = change in measured concentrations in any particular time period, considered a linear approximation of a concentration vs. time curve Larger time interval = greater deviation of average rate from instantaneous rate Rate correct answers = generally, a change in something (in this case, concentration) over a time period For a reaction A -- B, rate = - change [A]/change in time = change [B]/change in time Negative sign = reactants being USED UP (because by convention, we always want rate to be a positive value!) Rates measured in chemical kinetics: - Average rate - Instantaneous rate - Initial rate Reaction Rate VS Time correct answers As time goes on, the rate of a reaction generally slows down because the concentration of the reactants decreases At some point, the reaction stops, either because the reactants run out or because the system has reached equilibrium Instantaneous Rate correct answers = change in concentration at any one particular time period - Value for instantanous rate = slope of a line tangent to the curve at that particular point (first derivative of the function) Initial rate correct answers = instantaneous rate at time zero, t(0) - often the RATE OF INTEREST to chemist Reaction Rate Constant correct answers The rate of change will give a different value depending on which reactant/product you use. So to be consistent, the change in the concentration of each substance is multiplied by 1/stoichiometry coefficient. For a reaction aA + bB -- cC + dD, the rate = -1/a x delta[A]/delta t = -1/b x delta [B]/delta t = + + 1/c x delta [C]/delta t = + 1/d x delta [D]/delta t Measuring reaction rate in the lab correct answers To measure reaction rate, you need to be able to measure the concentration of at least 1 COMPONENT in the mixture at many points in time Some reactig ons occur slowly enough that samples can be periodically withdrawn from the reaction vessel + analyzed to determine the progress of the reaction 3 techniques are commonly used to monitor a reaction mixture: - Polarimetry - Spectroscopy = involves a light source + monochromator - Gas Chromatography = involves a carrier gas supply + oven Creating chemical rate laws correct answers Generally, we know reactions slow down when reactants are used up, and we can predict the way that reactions are going to occur based on familiar interactions. So, we should be able to come up with a mathematical expression for the rate of any reaction. We can consider reaction rates in terms of reactants or products. By convention, we've decided to use reactants to describe the reaction rate. Rate law = equation relating CONCENTRATION of reactants to RATE of the reaction (only applies when the reverse reaction is negligible) Rate of a reaction is directly proportional to the concentration of each reactant raised to a power: for the reaction A -- Products, Rate = k[A]^n n = "order of the reaction" with respect to that reactant (usually an integer that determines rate dependence on reactant concentration) (overall) order of reaction = sum of exponents on the reactants k = "rate constant" (constant for a particular reaction Average/Relative Rates VS Rate Laws correct answers For a reaction 2A -- 3C Average/relative rate: -1/a delta [A]/delta t = + 1/c delta [C]/delta t - Based on stoichiometric coefficients - Rates can be determined for ANY time period throughout the reaction, using ANY concentration difference of reactants/products Rate Law: k[A]^n - NOT based on stoichiometric coefficients, so the order of the reaction (n) must be determined EXPERIMENTALLY! - Only INITIAL (instantaneous) rates can be used - Only INITIAL concentration of REACTANTS can be used We use "Method of Initial Rates", where the same reaction is performed many times but the starting concentrations of reactants are varied + corresponding initial rates are determined. Then, we determine how rate is impacted by changes of initial reactants - this is how we create rate laws for all reactions! Overall Order of Rate Laws correct answers - If the reaction is ZERO ORDER (n = 0), the rate of the reaction is always the same regardless of how much [A] is present (concentration of reactants has no effect on rate) Doubling initial [A] will have NO EFFECT on the reaction rate either