CHM142 Final Exam Review with correct solutions

A positively charged particle and a negatively charged particle are initially far apart. What happens to their electrostatic potential energy as they are brought closer together? - ANS-- decreases Does the potential energy of the two particles increase or decrease when the distance is increased? - ANS-- increase If allowed to move, will protons be repelled or attracted to one another? - ANS-- Electrostatic repulsion is much greater than gravitational attraction and the protons move apart When a system does work on its surroundings, w will be a ________ value - ANS-- negative When a system ________, ΔE is always negative - ANS-- gives off heat and does work Of the following, which one is a state function? - ANS-- H Which of the following cannot leave or enter a closed system: heat, work, or matter? - ANS-- matter Which cannot leave or enter an isolated system? - ANS-- matter, work, and heat What do we call the part of the universe that is not part of the system? - ANS-- surroundings From the viewpoint of the chemical reactants as the system, what do you expect for the signs of q and w in this process? - ANS-- both of the signs should be negative Which of the following is an endothermic process? - ANS-- ice melting and boiling soup Would the measured heat change represent ΔHΔH or ΔE? - ANS-- ΔE If there is a difference, which quantity is larger for this reaction? - ANS-- ΔEΔH According to the definition of enthalpy, H =E + (PV), so ΔH =Δ E + Δ(PV). For an ideal gas at constant temperature and volume, Δ(PV) = V ΔP =RTΔn. For this reaction, Δn is negative. Thus VΔP or Δ(PV) is negative. Because ΔH = ΔE + Δ (PV), the negative Δ(PV) term means that ΔE is larger than ΔH. - ANS-- . Under what condition will the enthalpy change of a process equal the amount of heat transferred into or out of the system? - ANS-- when a process occurs under constant external pressure During a constant-pressure process, the system releases heat to the surroundings. Does the enthalpy of the system increase or decrease during the process? - ANS-- the enthalpy of the system decreases In a constant-pressure process, ΔH = 0. What can you conclude about ΔE, q, and w? - ANS-- q = 0 and ΔE = w Of the following, ΔH°f is not zero for ________. - ANS-- F_2 (s) What is meant by the term standard conditions, with reference to enthalpy changes? - ANS-- P = 1 atm, TT= 298 K What is meant by the term standard enthalpy of formation? - ANS-- This is the enthalpy change that accompanies formation of one mole of a substance from elements in their standard states What is the value of the standard enthalpy of formation of an element in its most stable form? - ANS-- ΔH∘f = 0 Which is more stable at room temperature, an O2 molecule or two separate O atoms? - ANS-- O2 molecule The process of solute particles being surrounded by solvent particles is known as ________ - ANS-- solvation If you put a drop of food coloring in water and watch the drop disperse, is entropy increasing or decreasing? - ANS-- Entropy is increasing Why doesn't NaCl dissolve in nonpolar solvents such as hexane, C6H14? - ANS-- Interactions between ions and nonpolar molecules tend to be very weak. Thus, the energy required to separate the ions in NaCl is not recovered in the form of ion-C6H14 interactions The oxygen atom in a water molecule points towards the sodium ion because its partial negative charge is attracted to the sodium ion's positive charge. This is called ion-dipole interaction - ANS-- . Which atom of water is associated with the cation? - ANS-- Oxygen atom, because the partial negative charge is localized on the oxygen atom Which solid will be more soluble in water, the one with the larger lattice energy or the one with the smaller lattice energy? - ANS-- The ionic solid with the smaller lattice energy T/F a solute will dissolve in a solvent if solute-solute interactions are weaker than solute-solvent interactions - ANS-- True T/F when a solution is made, the entropy of mixing is always a negative number - ANS-- False T/F a decrease in entropy favors mixing - ANS-- False A supersaturated solution _________ - ANS-- will rapidly precipitate if a seed crystal is added A solution with a concentration higher than the solubility is ______ - ANS-- supersaturated If you held the temperature and partial pressure of a gas over a liquid constant while doubling the volume of the liquid. Which statement below is true? - ANS-- the concentrations of gas molecule in the liquid is unchanged Molarity changes with a change in temperature. Molarity is defined as moles solute per unit volume of solution - ANS-- . Molality does not change with a change in temperature. Molality is defined as moles solute per kilogram of solvent - ANS-- . T/F adding a nonvolatile solute to a solution decreases the vapor pressure of the solution - ANS-- true T/F the value of the boiling-point elevation constant (Kb) depends on the identity of the solvent - ANS-- True As the concentration of a solute in a solution increases, the freezing point of the solution _________ and the vapor pressure of the solution _____ - ANS-- decreases, decreases What happens if a solute is added to a saturated solution? - ANS-- the added solute provides a template for the solid to begin to crystalize from solution, and a precipitate will form T/F NaCl dissolves in water but not in hexane because the water-ion interactions are stronger than hexane-ion interactions - ANS-- True T/F NaCl dissolves in water but not in hexane because the enthalpy of mixing NaCl with water is more negative than that of mixing NaCl with hexane - ANS-- True T/F NaCl dissolves in water but not in benzene because there are no hydrogen bonds in benzene - ANS-- False At equilibrium, ___________ - ANS-- the rates of the forward and reverse reactions are equal T/F the value of Kc depends on the starting concentrations - ANS-- False If Qc Kc, how must the reaction proceed to reach equilibrium? - ANS-- The reaction will proceed in the direction of more reactants, to the left According to the Arrhenius concept, an acid is a substance that ________ - ANS-- causes an increase in the concentration of H+ in aqueous solutions The conjugate base of HClO4 - ANS-- ClO4- Given that HClO4 is a strong acid, how would you classify the basicity of ClO4-? - ANS-- Negligible basicity T/F the value of Kw is always 1.0*10^-14 - ANS-- False Is it possible for a solution to have a negative pH? - ANS-- impossible What feature must any molecule or ion have in order to act as a Lewis acid? - ANS-- It must have an empty orbital T/F the extent of ionization of a weak electrolyte is increased by adding to the solution a strong electrolyte that has an ion in common with the weak electrolyte - ANS-- False Which of the following could be added to a solution of acetic acid to prepare a buffer? - ANS-- Sodium acetate or sodium hydroxide T/F The more negative ΔG° is for a given reaction, the larger the value of the corresponding equilibrium constant, K. - ANS-- True If ΔG° for a reaction is equal to zero, then ________ - ANS-- K = 1 The first law of thermodynamics - ANS-- ΔE = q + w When a system is at equilibrium _____ - ANS-- the process is not spontaneous in either direction A reversible process - ANS-- can be reversed with no net change in either system or surroundings T/F the melting of a substance at its melting point is an isothermal process - ANS-- True For an isothermal process, ΔS = - ANS-- qrev / T The second law of thermodynamics - ANS-- for any spontaneous process, the entropy of the universe increases T/F The entropy of the universe increases for any spontaneous process. - ANS-- True T/F The entropy change for an isothermal process depends on both the absolute temperature and the amount of heat reversibly transferred - ANS-- True T/F The entropy of the system must increase in any spontaneous process - ANS-- False T/F The entropy change of the system is equal and opposite that of the surroundings for any irreversible process - ANS-- False During a phase change, the temperature remains constant but the entropy change can be large as molecules increase their degrees of freedom and motion - ANS-- . At constant temperature and pressure, which statement gives the relationship between the sign ΔG and the spontaneity of the reaction? - ANS-- When ΔG 0, the forward reaction is spontaneous Is the standard free-energy change, ΔG∘, always larger than ΔG? - ANS-- No For any process that occurs at constant temperature and pressure, what is the significance of ΔG=0? - ANS-- the system is at equilibrium For a certain process, ΔG is large and negative. Does this mean that the process necessarily has a low activation barrier? - ANS-- No A reaction that is not spontaneous at low temperature can become spontaneous at high temperature if ΔH is _____ and ΔS is ______ - ANS-- + ,+ T/F If something is oxidized, it is formally losing electrons - ANS-- True T/F if there are no changes in the oxidation state of the reactants or products of a particular reaction, that reaction is not a redox reaction - ANS-- True Do free electrons appear anywhere in the balanced equation for a redox reaction? - ANS-- No, free electrons do not appear in the balanced equation for a redox reaction T/F The electrode where reduction occurs is called the anode - ANS-- false T/F the voltaic cell electrons flow from the anode to the cathode - ANS-- True The purpose of the salt bridge in an electrochemical cell - ANS-- maintain electrical neutrality in the half-cells via migration of ions an electrode at which oxidation occurs - ANS-- anode T/F When the cell potential is negative in a voltaic cell, the cell reaction will not proceed spontaneously - ANS-- True Of the following, only ________ is a valid unit for reaction rate - ANS-- mol/L-hr Which of the following would lead to an increased rate of reaction for gaseous reactants? - ANS-- increasing the temperature of the reactants T/F the overall reaction order is the sum of the orders of each reactant in the rate law - ANS-- True A reaction was found to be third order in A. Increasing the concentration of A by a factor of 3 will cause the reaction rate to _____ - ANS-- increase by a factor of 27 T/F the rate of a second order reaction can depend on the concentrations of more than one reactant - ANS-- True T/F the half-life for a first order rate law depends on the starting concentration - ANS-- False Under constant conditions, the half-life of a first-order reaction - ANS-- can be calculated from the reaction rate constant, is the time necessary for the reactant concentration to drop to half its original value, does not depend on the initial reactant concentration, and is constant How does the presence of a catalyst affect the activation energy of a reaction? - ANS-- a catalyst decreases the activation energy of a reaction T/F if you double the temperature for a reaction, you cute the activation energy in half - ANS-- False T/F Exothermic reactions are faster than endothermic reactions - ANS-- False T/F If you measure the rate constant for a reaction at different temperatures, you can calculate the overall enthalpy change for the reaction - ANS-- False As the temperature of a reaction of increased, the rate of the reaction increases because..... - ANS-- reactant molecules collide more frequently and with greater energy per collision In the energy profile of a reaction, the species that exists at the maximum on the curve - ANS-- activated complex In general, as temperature goes up, reaction rate - ANS-- goes up regardless of whether the reaction is exothermic or endothermic T/F the rate limiting step in a reaction is the slowest step in the reaction sequence - ANS-- True Of the following, ________ will lower the activation energy for a reaction - ANS-- adding a catalyst for the reaction Gamma rays - ANS-- neutral, strongest of the three beta rays - ANS-- negatively charged, medium strength Alpha rays - ANS-- positively charged, weakest of the three T/F radioactive decay is a first order kinetic process - ANS-- True If the size of a radioactive sample is doubled, what happens to the activity of the sample in Bq? - ANS-- the activity of the sample doubles. the number of disintegrations per second is proportional to the number of atoms or radioactive nuclei Due to the nature of the positron, __________ is actually detected in positron emission tomography - ANS-- gamma radiation