Chem II Aktiv Final Practice 12-21
The pH of a basic solution is 9.77. What is [OH⁻]?
.To determine the concentration of OH− in the solution with a pH of 9.77, we can first find the pOH of the solution: pOH=14.00−pH pH=4.23 To find the concentration of OH− we can use the relationship: [OH−]=10−pOH So if the pOH = 4.23, then [OH−]=10^−4.23 =5.9×10−5M
Consider the multistep reaction. What is the best rate law for the overall reaction? 2A + B -> C + D (slow) C <=> 2E (fast) A) Rate = k₁[A][B][C] B) Rate = k₂[C] C) Rate = k₁[A]²[B] D) Rate = (k₁[A][B])/(k₂[C]) E) Rate = k₁k₂[A]²[B]
Fast reactions following the slow step in a mechanism do not enter into the rate law, so C and k₂ will not be part of the rate law. The slow step involves only A and B and it is a termolecular reaction. Therefore the best rate law of the overall reaction would be Rate = k₁[A]²[B]. C
Compared to HCO₃⁻, H₂CO₃ has a A) Higher Ka B) Lower Ka C) Lower pKa D) Higher pKa E) Both (A) and (C)
For a given polyprotic acid, the more (H+) ions you remove, the stronger the remaining (H+) ions will be held. This results in a lower (Ka) for the remaining (H+). (H2CO3) has two H atoms compared to (HCO3−), thus a higher (Ka) A high (Ka) would have a lower (pKa) E
In a voltaic (galvanic) cell, oxidation occurs at the _____ and is where _____ in the salt bridge moves toward. A) cathode, anions B) cathode, cations C) anode; anions D) anode, cations E) salt bridge, both cations and anions
Oxidation occurs at the anode. As the electrons are removed from the solution, electrical neutrality is maintained as anions (negative ions) in the salt bridge move into the solution. C
Which of the following is true for a reaction at equilibrium? A) The rate of the forward reaction is greater than the rate of the reverse reaction. B) The rate of the forward reaction is less than the rate of the reverse reaction. C) The rate of the forward reaction is equal to the rate of the reverse reaction. D) The rates of the forward and reverse reactions become zero because the reaction stops. E) The rates of the forward and reverse reactions can no longer be determined.
When a reaction is at equilibrium there is no further change in the concentrations of the reactants and products. That means they must be formed at the same rate as they are breaking down, so the rate of the forward reaction is equal to the rate of the reverse reaction. C
When a system is at dynamic equilibrium, A) no reactions are occurring. B) a reaction is occurring in only one direction. C) the rates of the forward and reverse reactions are equal. D) all of the reactants have been converted to products
When a system is at dynamic equilibrium, the rates of the forward and reverse reactions are equal. C
What can be said about the concentrations of reactants relative to the concentrations of products at equilibrium? A) [Reactants] = [Products] B) [Reactants] > [Products] C) [Reactants] < [Products] D) [Products]/[Reactants] = Constant
When a system is at dynamic equilibrium, the rates of the forward and reverse reactions are equal. The concentrations of the reactants remain constant at equilibrium and so do the concentrations of the products. Therefore, the ratio between them will be constant at equilibrium. D
Which one of the following titrations is expected to have a pH < 7 at the equivalence point? A) HNO₃ titrated with LiOH B) HNO₂ titrated with KOH C) NaNO₂ titrated with HBr D) NaNO₃ titrated with HBr
When strong acids are added to a weak base, the conjugate acid that is formed in the reaction also reacts with water to produce more H+. This results in a lower pH. C
A reaction is determined to have the rate law rate = k[NO]²[H₂]. What is the rate-determining step in the mechanism? A) Step 1: 2NO<=>N2O2 B) Step 2:N2O2+H2->N2O+H2O C) Step 3: N2O+H2->N2+H2O D) Cannot be determined from the rate law
You can determine which step is rate-determining. To determine the rate law for a mechanism containing an equilibrium step, you must redefine the intermediate in terms of the equilibrium step. You cannot have any intermediates in the rate law. The rate determining step is Step 2.
Which of the following is true for a process where ∆S(universe) < 0 at 298 K? A) It is exothermic B) It is nonspontaneous. C) It is product-favored. D) It is spontaneous. E) It is endothermic.
Any spontaneous process must increase the entropy of the universe, according to the second law of thermodynamics B
Which of the following is a Lewis acid? A) Fe³⁺ B) CN⁻ C) NH₃ D) SCN⁻
A Lewis acid is an electron pair acceptor. From this list, Fe3+ is the Lewis acid.
For each of the following processes, determine the sign on the entropy and the best explanation for that sign. A gas is cooled at constant pressure from 40 °C to 20 °C. A) ∆S > 0 because the gas decreased in volume. B) ∆S < 0 because the gas decreased in volume. C) ∆S = 0 because the pressure does not change. D) ∆S > 0 because the gas decreased in temperature. E) ∆S < 0 because the gas decreased in temperature.
A decrease in temperature means there are fewer microstates available for the gas. Fewer microstates means a lower entropy according to Boltzmann's law. E
For each of the following processes, determine the sign on the entropy and the best explanation for that sign. A gas is compressed at constant temperature from 4.0 L to 2.0 L. A) ∆S > 0 because the gas has less volume available to it. B) ∆S < 0 because the gas has less volume available to it. C) ∆S = 0 because the temperature does not change. D) ∆S > 0 because the pressure of the gas had to increase. E) ∆S < 0 because the pressure of the gas had to increase.
A decrease in volume means there are fewer microstates available for the gas. Fewer microstates means a lower entropy according to Boltzmann's law. B
If a plot of 1/[A] versus time produces a straight line with a positive slope for the reaction A → B + C, what is the order of the reaction? A) Zero B) First C) Second D) Third E) Cannot determine order from this information
A graph of 1/[A] versus time yields a straight line with a positive slope for second order reactions. C
Galvanized is a term associated most closely with which metal? A) Fe B) Cr C) Hg D) Zn E) Pb
A metal such as iron is galvanized by coating it with a more easily oxidized metal that protects the iron from corrosion, acting as an anode and forcing the iron to act as a cathode. Zn is the most easily oxidized metal in the list, and is the one commonly used to galvanize other metals. D
If a chemical reaction has a negative ∆H and a positive ∆S, then A) it will be spontaneous at all temperatures. B) it will be non-spontaneous at all temperatures. C) it will be spontaneous at high temperatures and non-spontaneous at low temperatures. D) it will be spontaneous at low temperatures and non-spontaneous at high temperatures. E) the absolute entropy of the reactants will be less than 0.
A negative ΔG means a process is spontaneous, and a positive ΔG is always non-spontaneous. ΔG=ΔH−TΔS and T is always positive since it is in kelvin. A chemical reaction having a negative ΔH and a positive ΔS will always have a negative ΔG and will always be spontaneous. A
Which of the following solutions would be expected to have a pH greater than 7.00? Weak Acid Kₐ Weak Base Kb HCN 4.9 x 10⁻¹⁰ HONH₂ 1.1 x 10⁻⁸ HNO₂ 4.5 x 10⁻⁴ NH₃ 1.8 x 10⁻⁵ HIO 2.3 x 10⁻¹¹ C₆H₅NH₂ 4.3 x 10⁻¹⁰ HBrO 2.5 x 10⁻⁹ H₂NNH₂ 1.3 x 10⁻⁶ C₆H₅COOH 6.3 x 10⁻⁵ C₅H₅N 1.7 x 10⁻⁹ A) NH₄Br B) C₆H₅NH₃Br C) Ca(NO₃)₂ D) C₆H₅COONa
A pH greater than 7 indicates the presence of a proton acceptor rather than a proton donor. NH4+ and C6H5NH3+ are protic ions, with hydrogens attached to electronegative nitrogen, so they are proton donors. NO3− and C6H5COO− are possible proton acceptors, but NO3- is the conjugate base of a strong acid (nitric acid, pKa -1.5) whereas C6H5COO− is the conjugate base of a weak acid (benzoic acid, pKa 4). C6H5COO− is the strongest proton acceptor and raises the pH above 7. D
Consider the reaction below. Which of the following would increase the partial pressure of C at equilibrium? A (g) + B (g) ⇌ C (g) ΔH > 0 A) removing B. B) increasing the temperature. C) decreasing the total pressure. D) adding a catalyst.
A positive ΔHΔH indicates that this is an endothermic reaction with energy being required for the forward reaction to occur. Increasing the temperature would shift the reaction to the right to create more products to reach equilibrium. B
A battery that cannot be recharged is classified as a _____ A) primary battery B) secondary battery C) fuel cell D) electrolytic cell
A primary battery is one that designed to be used once and discarded. The electrochemical reaction in the cell is not reversible. A secondary battery can be recharged.
Which of the following is not true about a spontaneous process? A) A spontaneous process is one that continues on its own once begun. B) Spontaneous processes occur naturally. C) A nonspontaneous process does not occur unless some external action is applied. D) A nonspontaneous process does not mean it cannot ever occur under any conditions. E) A spontaneous process is also spontaneous in the reverse direction.
A spontaneous process will continue on its own once begun. Spontaneous processes occur naturally and nonspontaneous processes do not occur unless some external action is applied. E
Which of the following are spontaneous processes? 1. Ice melting at 1atm and 298 K (assume only ice is initially present). 2. Heat flowing from a hot object to a cold object. 3. An iron bar rusting.
All three of these processes are spontaneous and occur naturally.
Spontaneous processes are ones that occur quickly and have a low activation energy. A) False. Spontaneous processes always require an input of energy to overcome the activation energy, but always react quickly. B) False. Spontaneous processes can occur slowly, but always have a low activation energy. C) False. Spontaneous reactions can react slowly and can have a high activation energy. D) False. Spontaneous processes always react slowly and always have a high activation energy. E) True.
Although a spontaneous reaction has negative free energy and is thermodynamically favorable, the kinetics are not necessarily fast. Rusting and the conversion of diamond to graphite are both spontaneous processes that occur slowly and have a high activation energy C
Why does aluminum (Al) metal not undergo corrosion like iron does? A) Al does not easily react with oxygen. B) Fe gives cathodic protection to Al. C) A protective layer of Al₂O₃ forms on the surface of Al. D) Al is more difficult to oxidize than Fe. E) An electrical circuit cannot be completed on a surface of Al.
Aluminum is easily oxidized to Al2O3, but the surface layer of Al2O3 formed serves as a protective coating to the Al. C
For the electrochemical cell represented by Cr²⁺ | Cr³⁺ || Li⁺ | Li, E°(cell) = -2.63 V. This cell: A) Runs spontaneously B) Does not run spontaneously C) Is galvanic D) Is electrolytic E) Both (B) and (D)
An electrochemical cell with a negative voltage is not spontaneous, so it occurs only if electrical energy is applied. Therefore both does not run spontaneously and is electrolytic is correct. E
A galvanic cell Zn | Zn²⁺ || Ni²⁺ | Ni runs spontaneously. If a current is imposed to turn this into an electrolytic cell, which of the following will occur? A) Zn(s) still gets oxidized at the same rate B) Zn(s) gets oxidized at a faster rate C) Ni²⁺ gets oxidized D) Ni²⁺ gets reduced E) Zn²⁺ gets reduced
An electrolytic cell runs in the opposite direction of a galvanic cell. Applying a current to the galvanic cell Zn | Zn2+ || Ni2+ | Ni would convert the Zn anode to a cathode and cause Zn2+ to be reduced. E
An electrolytic cell converts: A) Chemical energy into electrical energy B) Chemical energy into mechanical energy C) Mechanical energy into electrical energy D) Electrical energy into chemical energy
An electrolytic cell uses an electric current to produce a chemical reaction, so it converts electrical energy into chemical energy. D
Using the information in the table, the rate law for the reaction 2 A(g) + B(g) → C(g) + D(g) is [A]₀ (M) [B]₀ (M) Rate (M/s) 0.100 2.50 0.460 0.200 2.50 0.920 0.300 1.25 1.38 A) Rate = k[A][B] B) Rate = k[B] C) Rate = k[A]²[B] D) Rate = k[A]
As the concentration of the of A is doubled while B is held constant, the rate is doubled. As the concentration of B is reduced by half, the rate is only affected by the change in concentration of A. The formula representing rate would be: Rate = k[A]. D
Magnesium chloride is a salt that dissolves in water according to the reaction: MgCl₂(s) ⇌ Mg⁺²(aq) + 2Cl⁻(aq). What is the expression for its equilibrium constant? A) K=[Mg⁺²][Cl⁻]/[MgCl₂] B) K=[Mg⁺²][Cl⁻]² C) K=[Mg⁺²][Cl⁻] D) K=[Mg⁺²][Cl⁻]²/[MgCl₂]
Compounds which are solids and liquids have constant composition and therefore do not appear in the equilibrium expression. Equilibrium constants are the products divided by the reactants. Coefficients become exponents. In this case, the equilibrium constant would be Kc=[Mg2+][Cl−]^2 B
Which of the following pairs of substances has the species with the higher entropy listed first? A) Na(s), Na(l) B) Mg(NO₃)₂(s), Mg(NO₃)₂(aq) C) Ca(s), UF₆(g) D) Ni(s), Br₂(l) E) Ar(g), Hg(l)
Entropy is a measure of disorder. Gases are more disordered and have the highest entropy values. Perfect crystalline solids have an entropy of 0 at absolute zero temperature because they are highly ordered and solids have higher entropies than perfect crystals but lower entropies than liquids. Liquids have entropies that are lower than gases but higher than solids. E
For a particular reaction, K = 1.67. What can be said about this reaction? A) There are many more products than reactants in the equilibrium mixture. B) There are many more reactants than products in the equilibrium mixture. C) There are roughly equal amounts of reactants and products in the equilibrium mixture. D) The reaction has not yet reached equilibrium because K does not equal 1.
Equilibrium constants are products divided by reactants. A small number indicates that the denominator is larger and a large number indicates that the numerator is larger. If K=1.67, this indicates that there are roughly equal amounts of reactants and products in the equilibrium mixture. C
If Kp is the equilibrium constant for the reaction 2 A (g) + B (g) ⇌ 3 C (g). What is the equilibrium constant (in terms of Kp) for the reaction 6 A (g) + 3 B (g) ⇌ 9 C (g)? A) I (Kp)^1/3 B) II (Kp)^-1/3 C) III (Kp)^3 D) IV (Kp)^-3
Equilibrium constants are the products divided by the reactants. Coefficients become exponents. Because of this, multiplying the coefficients by 3 results in an exponent of 3. C
Consider the equilibrium constant below. Which of the following reactions matches this equilibrium constant? Kc= [C]^3/[A] A) A (s) + B (aq) ⇌ 3 C (aq) B) A (l) + B (s) ⇌ 3 C (l) + D (s) C) A (aq) + B (s) ⇌ 3 C (aq) D) A (aq) ⇌ C (aq)
Equilibrium constants are the products divided by the reactants. Coefficients become exponents. In this case, the equilibrium constant shows that the product is C and the reactant is A. It also shows the coefficient for C is 3. Compounds which are solids and liquids have constant composition and therefore do not appear in the equilibrium expressions, so they can also be part of the chemical reaction. At minimum, the balanced chemical reaction would be A ⇌3CA ⇌3C. A and C can either be in gaseous or aqueous form. C
Consider the following chemical reaction at equilibrium: HF(aq) + H₂O(l) ⇌ H₃O⁺(aq) + F⁻(aq) If one drop of aqueous hydrochloric acid (HCl) is added, in which direction will the equilibrium (Q) shift? A) reactants B) products C) neither the reactants nor the products
Hydrochloric acid (HCl) is a strong acid, and dissociates to form H⁺ ions that react with the strongest base present in solution, fluoride (F−) to form hydrofluoric acid (HF). This causes Q to be greater than Keq, and the equilibrium shifts towards reactants to decrease Q to equal Keq. A
If the equilibrium constant of a given reaction is 2.54 what is the equilibrium constant of its reverse reaction?
If a reaction is reversed, the equilibrium constant expression is inverted. 1/2.54=0.394
Which is true for the endothermic reaction 2 SO₃(g) → 2 SO₂(g) + O₂(g)? A) Spontaneous at all T B) Spontaneous at low T C) Non-spontaneous at any T D) Spontaneous at high T
If both ΔH and ΔS are positive, then T must be large in order for ΔG to be negative. D
Consider the following acidic equilibrium: H₂CO₃(aq) + H₂O(l) ⇌ HCO₃⁻(aq) + H₃O⁺(aq). If you add NaHCO₃ to this solution, which of the following will occur? A) The reaction quotient will decrease. B) The reaction will shift in the reverse direction. C) The equilibrium constant will increase. D) No changes to the equilibrium positions will take place.
If you add NaHCO3NaHCO3 to this solution, the reaction will shift in the reverse direction to reestablish equilibrium B
At the equivalence point for the titration of HCN with KOH, the pH is expected to be A) 7 B) greater than 7 C) less than 7
In addition to the base being used in the titration, the conjugate base that is formed in the reaction with the weak acid also reacts with water to produce more OH−. This results in a higher pH B
Which of the following combinations can be used to make a buffer? (Assume equal volumes are used.) A) 0.30 M HCN and 0.30 M HBr B) 0.30 M HCN and 0.15 M HBr C) 0.30 M HCN and 0.30 M NaOH D) 0.30 M HCN and 0.15 M NaOH
In order to have a buffer you need an acid and its conjugate weak base in approximately equal concentrations. The partial neutralization of the weak acid by the strong base produces the weak conjugate base, CN−. Because the volume amounts of NaOH and HCN are equal, and the concentration of HCN is twice that of NaOH, this means that about half of the HCN will be neutralized, giving a buffer with roughly equal amounts of HCN and its conjugate base CN−. D
What is the smallest whole-number coefficient for H₂S when the equation H₂S + MnO₄⁻ → Mn²⁺ + SO₄²⁻ is balanced in acidic solution?
In the equation S increases in oxidation number from -2 to +6, losing 8 electrons, and Mn decreases in oxidation number from +7 to +2, gaining 5 electrons. The only way to balance the electrons is to give H2S a coefficient of 5 and MnO4− a coefficient of 8, resulting in a transfer of 40 electrons in the balanced equation. 5
Which of the following is the cell diagram for the reaction 3 Pb²⁺+(aq) + 2 Al(s) → 3 Pb(s) + 2 Al³⁺(aq) A) Pb(s) | Pb²⁺(aq) || Al³⁺(aq) | Al(s) B) Pb²⁺(aq) | Pb(s) || Al³⁺(aq) | Al(s) C) Pb(s) | Pb²⁺(aq) || Al(s) | Al³⁺(aq) D) Al(s) | Al³⁺(aq) || Pb²⁺(aq) | Pb(s) E) Al³⁺(aq) | Al(s) || Pb(s) | Pb²⁺(aq)
In the reaction 3Pb2+(aq)+2Al(s) →3Pb(s)+2Al3+(aq) Al is being oxidized at the anode and Pb2+ is being reduced at the cathode, so the cell diagram is Al(s) | Al3+(aq) || Pb2+(aq) | Pb(s) D
Which of the following will decrease the rate of a reaction? A) Adding a catalyst to the reaction. B) Increasing the temperature. C) Decreasing the surface area of a solid reactant. D) Increasing the concentration of the reactants.
Increasing the surface area of the reactants increases the reaction rate. The more surface area, the higher the likelihood that the reactants will collide and react. The rate of reaction is affected by the concentration of the reactants, the presence of a catalyst, the surface area of the reactants, and the temperature of the reaction. Removing or decreasing each of these would result in a decreased reaction rate. C
The Haber Process: N₂ + 3H₂ → 2NH₃ is an important industrial route for the production of ammonia. However, the reaction does not occur fast enough at room temperature to be useful. What could be done to increase the rate of this reaction the most?
Increasing the temperature increases the average kinetic energy of molecules resulting in more successful collisions. Catalysts increase the rate of reactions by lowering the activation energy. Both are useful strategies, and both are used in combination to increase the reaction rate the most in the Haber Process. E
Determine the sign on the entropy and the best explanation for that sign. A gas in a 10.0 L container is mixed with another gas while the temperature remains constant. A) ∆S > 0 because the original gas has less volume available. B) ∆S < 0 because the original gas has less volume available. C) ∆S = 0 because the temperature does not change. D) ∆S > 0 because there are more particles of different types present. E) ∆S < 0 because there are more particles of different types present.
Introducing more particles, especially more particles of a different type means that the number of microstates has increased. More microstates mean a higher entropy according to Boltzmann's law. D
What species are made at the anode and cathode, respectively, during the electrolysis of molten KBr? A) Br⁻(aq) and K⁺(aq) B) K(l) and Br⁻(aq) C) Br₂(g) and K(l) D) Br₂(g) + KBr(l) E) Br⁻(aq) + K(l)
Oxidation occurs at the anode, so Br2(g) is formed from oxidation of Br−, at the anode. Reduction occurs at the cathode, so K(l) is formed from reduction of K+ at the cathode. C
Which of the following has the largest standard molar entropy, S° (298.15 K)? A) He(g) B) H₂(g) C) NaCl(aq) D) KBr(s) E) Hg(l)
Perfect crystalline structures have an entropy of 0 because they are highly ordered. Gases have high entropy because they are very disordered and are random. Larger or heavier molecules have higher entropies. H2 has a larger standard molar entropy than He when both are in gaseous form because the H2 molecule has two atoms compared to a single atom of He. This means there are more microstates available for H2, so it will have the largest standard molar entropy. B
Which of the following guarantees a reaction will be spontaneous? A) ∆H > 0 B) ∆S(sys) > 0 C) ∆H < 0 D) ∆S(surr) > ∆S(sys) E) ∆S > ∆H/T
Positive values for ΔG indicate that the reaction will be nonspontaneous and negative values for ΔG indicate that the reaction will be spontaneous. E
If the reaction quotient (Q) is equal to the equilibrium constant (K) for a reaction then A) the reaction will proceed toward products. B) the reaction will proceed towards reactants. C) the reaction is at equilibrium and the reaction will stop completely. D) the reaction is at equilibrium and the reaction will proceed at equal rates in the reverse and forward direction. E) The reaction equation is required to answer this question.
Q is a ratio of products and reactants at a given time and K is the ratio of products and reactants at equilibrium. If Q is equal to K, then the reaction is at equilibrium; however, chemical equilibrium is a dynamic process. Both forward and reverse reactions are occurring at the same rate. D
Consider the following chemical reaction at equilibrium: CO(g) + H₂O(g) ⇌ CO₂(g) + H₂(g) If H₂ is removed, how will Keq for the reaction change? A) increase B) decrease C) stay the same
Removing a product does not alter Keq, which depends on reaction temperature. C
Reversible processes: A) Do not conserve energy B) Do not conserve momentum C) Are impossible in real life D) Are possible only at high temperatures
Reversible processes can only be approximated in real life because no process is 100% efficient and there are energy losses in the forward and reverse directions. If a process were truly reversible, then it would result in perpetual motion and be a violation of the 2nd Law of Thermodynamics. C
cWhich of the followings statements is (are) true for a galvanic (voltaic) cell when E° = +1.00 V? 1. The reaction is spontaneous 2. At equilibrium, K = 1. 3. ∆G° is negative. A) 1 only B) 2 only C) 3 only D) 1 and 3 only E) 2 and 3 only
Since ΔG∘=−nF when E∘ = +1.00 V K does not equal 1 at equilibrium because K=e(nFE°/RT) =e(n×96500×1.0/8.314× 298) =e38.9n which is a large positive number D
As E°(cell) increases: A) ∆G° increases B) ∆G° decreases C) ∆G° remains the same D) Not enough info
Since ∆G°=−nFE°, ∆G° decreases as E°(cell) increases. B
A reaction which is exothermic and has an overall increase in entropy is A) spontaneous only at high T B) spontaneous only at low T C) always spontaneous D) spontaneous in the reverse direction.
Spontaneity is determined by the free energy. When ΔG is negative, it is spontaneous. ΔG=ΔH−TΔS The problem indicates that the ΔS is positive. If the reaction is exothermic, this means that the ΔH is negative. ΔG is going to be negative no matter the temperature. C
What is the rate law for the proposed mechanism? Step 1: H2 (g) + 2NO (g) -> N2O (g) + H2O(g) Step 2: N2O (g) +H2 (g) -> N2 (g) + H2O (g) A) rate = k[H₂][NO] B) rate = k[H₂]²[NO] C) rate = k[H₂][NO]² D) rate = k[H₂]²[NO]² E) rate = k[H₂][N₂O]
Step one is termolecular with a rate law: rate = k₁[H₂][NO]². This is the slow step in the mechanism. Fast steps following the slow step do not enter into the rate law, so the overall rate law is rate = k[H₂][NO]². C
Which of the following affects E(cell) under nonstandard conditions? A) Concentration of reactants B) Concentration of products C) Temperature D) All of the above
The E(cell) under nonstandard conditions is affected by all three conditions: temperature, the concentration of reactants, and the concentration of products. D
Salt A has a greater solubility in water than Salt B. What can be said about their Ksp values? A) Salt A has a larger Ksp than Salt B B) Salt B has a larger Ksp than Salt A. C) Their Ksp values cannot be compared because we do not know the number of ions each produces.
The Ksp is directly related to the number of ions produced and we don't know this. Therefore the Ksp cannot be compared C
Which of the following species is the best reducing agent? Standard Reduction Potentials E° (V) F₂(g) + 2e⁻ → 2F⁻(aq) 2.87 Ag⁺(aq) + e⁻ → Ag(s) 0.80 Cu²⁺(aq) + 2e⁻ → Cu(s) 0.34 Pb²⁺(aq) + 2e⁻ → Pb(s) -0.13 Mg²⁺(aq) + 2e⁻ → Mg(s) -2.36 A) Pb B) Ag⁺ C) Mg D) F⁻ E) Cu
The best reducing agent is the one most easily oxidized, which is the one with the lowest reduction potential. From the choices on the list, Mg, with a reduction potential of -2,36 V will be the best reducing agent. C
Which of the following does the change in the free energy of a reaction predict? A) the work done B) the speed C) the spontaneity D) the final temperature E) the heat released
The change in the free energy of a reaction predicts the spontaneity of a reaction. A positive change in free energy indicates a nonspontaneous reaction. A negative change in free energy indicates a spontaneous reaction.
The reaction C₃H₈(g) + 5O₂(g) ⟶ 3 CO₂(g) + 4 H₂O(l) can be continuously conducted in what type of device? A) primary battery B) secondary battery C) fuel cell D) electrolytic cell
The energy from a reaction such as C3H8(g)+5O2(g) →3CO2(g)+4H2O(l) can be harnessed to produce electricity directly in an electrochemical cell called a fuel cell, so-called because the source of energy is a replaceable fuel such as C3H8(g). C
Consider the following equilibrium reaction: A (g) + B (s) ⇌ C (g) If Kp = 6 × 10⁻³ which species will have the highest partial pressure at equilibrium?
The equilibrium constant is calculated by dividing the partial pressures of the products by the partial pressure of the reactants. Coefficients become exponents. Compounds which are solids and liquids have constant composition and therefore do not appear in the equilibrium expression. Kp=PC/PA If the Kp is less than 1, this indicates that the partial pressure of A is larger than the partial pressure of C. A
The reaction Q(g) + R(g) → Z(l) is shown to be exothermic. Which of the following is true concerning the reaction? A) It is spontaneous only at high T B) It is spontaneous only at low T. C) It is nonspontaneous at all T. D) It is spontaneous at all T. E) It is nonspontaneous only at low T.
The free energy can be calculated using this formula. ΔG=ΔH−TΔS An exothermic reaction has a −ΔH and this reaction decreases in entropy, yielding a −ΔS . The only way that the ΔG will be negative is if the temperature is low. B
Which set of results applies to a reaction that is spontaneous at 250 K but is nonspontaneous at 350 K? A) ∆H < 0 and ∆S > 0 B) ∆H > 0 and ∆S > 0 C) ∆H < 0 and ∆S < 0 D) ∆H > 0 and ∆S < 0
The free energy can be calculated using this formula. ΔG=ΔH−TΔS If the reaction is spontaneous at low temperatures and nonspontaneous at high temperatures, this indicates that the both the ∆H and ∆S are less than 0. C
If ∆H < 0 and ∆S < 0, a reaction will be: A) Spontaneous B) Nonspontaneous C) At equilibrium D) Not enough information
The free energy can be calculated using this formula. ΔG=ΔH−TΔS If ΔH<0 and ΔS<0, the spontaneity of the reaction depends on the temperature. If the temperature is low, ΔG will be negative and the reaction will be spontaneous. If the temperature is high, ΔG will be positive and the reaction will be nonspontaneous. D
Which of the following is true for a particular reaction if ∆G° is -40.0 kJ/mol at 290 K and -20.0 kJ/mol at 390 K? A) ∆H >0 , ∆S > 0 B) ∆H < 0, ∆S < 0 C) ∆H > 0, ∆S < 0 D) ∆H < 0, ∆S > 0
The free energy can be calculated using this formula. ΔG=ΔH−TΔS This shows that the reaction is spontaneous at both temperatures. Also, this shows that the reaction becomes less spontaneous at higher temperatures, because the value of delta-G gets larger at higher temperatures. B
Which one of the following 1.0 M solutions would have the lowest pH? Weak Base Kb C₅H₅N 1.7 x 10⁻⁹ HONH₂ 1.1 x 10⁻⁸ C₆H₅NH₂ 4.3 x 10⁻¹⁰ H₂NNH₂ 1.3 x 10⁻⁶ A) C₅H₅N B) HONH₂ C) C₆H₅NH₂ D) H₂NNH₂
The lower the Kb, the weaker the weak base. In this case, C6H5NH2 would be the weakest weak base in the list and would have the lowest pH. C
The reaction rate of a reaction at 60 °C will be greater than at 30 °C because _____ A) the higher temperature leads to greater surface area on solid or liquid reactants. B) the reactants at 60 °C will be moving with too great of a speed to collide effectively. C) the activation energy will be lower at 60 °C. D) there is a greater proportion of reactants with the necessary kinetic energy to react. E) there is a greater likelihood that the reactants will have the correct orientation to collide effectively.
The molecules are moving faster at higher temperatures. This increases the likelihood that they have enough kinetic energy to react. D
Which of the following will be the weakest acid? A) HBrO B) HBrO₂ C) HBrO₃ D) HBrO₄
The more electronegative oxygen atoms there are, the higher the acid strength. Out of this list, HBrO contains the fewest number of electronegative oxygen atoms and would be the weakest acid. A
Which of the following reactions would have the most positive ∆S° value? A) SO₂(g) + Na₂O(s) ⟶ Na₂SO₃(s) B) CO₂(s) ⟶ CO₂(g) C) Fe³⁺(aq) + SCN⁻(aq) ⟶ FeSCN²⁺(aq) D) N₂(g) + 3 H₂(g) ⟶ 2 NH₃(g) E) 2 NO(g) + Cl₂(g) ⟶ 2 NOCl(g)
The most positive change in entropy would indicate that there is more disorder at the end of the reaction. Option B goes from one mole of a highly ordered solid to one mole of a very disordered gas. B
What is the order of the reaction if A decomposes to B and C with a rate constant of 8.43 × 10⁻⁴ s⁻¹ at a certain temperature? A) Zero B) First C) Second D) Third E) Cannot determine order from this information
The order of a reaction can be determined from the units of the rate constant. The rate constant of this reaction has the units s−1s−1, so it is a first-order reaction. B
A decrease of pH by 3 implies A) The H⁺ concentration triples. B) The OH⁻ concentration decreases by a factor of 3. C) The OH⁻ concentration decreases by a factor of 1000. D) The H⁺ concentration decreases by a factor of 1000.
The pH of a solution is calculated by finding the negative base ten log of the concentration of H+. A solution with a low pH has more H+ ions than a solution with a high pH. Therefore, an decrease of pH by 3 would be 10×10×10=1000, and would be an increase of H+. Therefore, an increase of [H+] by a factor of 1000 indicates a decrease of [OH−] by a factor 1000. C
For the reaction 2 A + 3 B → 4 D + 5 E, how is the rate of reaction expressed in terms of rate of disappearance of B? A) ∆[B]/∆t B) -∆B/∆t C) +1/3∆[B]/∆t D) -1/3∆[B]/∆t E) +3∆[B]/∆t
The rate of a reaction is equal to the rate of change of a reactant or product, divided by its coefficient in the balanced equation, with negative values for reactants because they are disappearing and positive values for products. For the given reaction 2A+3B⟶4D+5E2A+3B⟶4D+5E the rate in terms of the change in [B] is given by rate=(−1/3)(Δ[B]/Δt)
Identify the molecularity of the elementary reaction below: Br₂(g) → 2Br･(g) A) unimolecular B) bimolecular C) termolecular D) quadmolecular
The reaction is unimolecular. Unimolecular reactions involve the rearrangement of one reactant molecule to produce two or more. One Br2 molecule splits into two ions. A
The reason complex ion formation can increase the solubility of insoluble compounds is A) the complex ions formed precipitate. B) the complex ions shift the solubility equilibrium forward by removing the cation from the solution C) the complex ions shift the solubility equilibrium in the reverse direction by adding extra ions to the solution. D) complex ions are more soluble in general.
The reason complex ion formation can increase the solubility of insoluble compounds is the complex ions shift the solubility equilibrium forward by removing the cation from the Ksp. B
Which of the following is true about the total entropy of the universe? A) It is always increasing B) It is always decreasing C) It remains constant at a given T D) It always remains constant
The second law of thermodynamics states that the entropy of the universe is always increasing. A
In the statement 'all spontaneous changes result in an increase in entropy', the entropy change is _____. A) ∆S(sys) B) ∆S(surr) C) ∆S(univ) D) ∆S°(rev)
The second law of thermodynamics states that the entropy of the universe is always increasing. C
What will the sign on ∆S be for the following reaction and why? 2 Mg (s) + O₂ (g) → 2 MgO (s) A) Positive, because there is a solid as a product. B) Positive, because there are more moles of reactant than product. C) Positive, because it is a synthesis reaction. D) Negative, because there are more moles of gas on the reactant side than the product side. E) Negative, because there are more moles of reactant than product.
The sign of ΔS can be determined by comparing the number of moles of gas on the reactant and product side. Since the number of moles of gas is decreasing, entropy is decreasing and thus is negative. D
How does the third law of thermodynamics allow absolute entropies of substances to be determined? A) It defines a reference point by which entropy changes can be measured and assigned as an absolute entropy for a substance. B) It defines the temperature at which all absolute entropies are measured. C) It provides a reference point for the absolute entropy of the universe. E) It requires that a process be reversible to measure the absolute entropy change.
The third law of thermodynamics defines a reference point by which entropy changes can be measured and assigned as an absolute entropy for a substance A
Which of the following best describes the third law of thermodynamics? A) ∆U(univ) = ∆U(sys) + ∆U(surr) B) S° = 0 for perfect Li(s) at 0 K C) ∆S(univ) > 0 (spontaneous process) D) ∆S = ∆H(rev)/T at constant T E) ∆G = ∆H - T∆S
The third law of thermodynamics states that the entropy for a perfect crystal is 0 at absolute zero temperature in Kelvin. B
Which of the following quantities is based on the third law of thermodynamics? A) ∆H°(f) = 0 for Fe(s) at 298 K B) ∆G°(f) = 0 for Br₂(l) at 298 K C) ∆G° > 0 when ∆H° = 169 kJ/mol and ∆S° = 78.1 J/mol ･ K for 2H₂S(g) ⟶ 2H₂(g) + S₂(g) D) S° = 64.89 J/mol ･ K for Pb at 298 K E) q = -198.2 kJ/mol for 2SO₂(g) + O₂(g) ⟶ 2SO₃(g)
The third law of thermodynamics states that the entropy for a perfect crystal is 0 at absolute zero temperature in Kelvin. Option D is the only one that deals with entropy.
The half-life of element X is 500 years. If there are initially 8 g of X, how much will remain after 1500 years?
There are 3 half-lives. Find the amount after each half life. 8/2=4 4/2=2 2/2=1 1g
Which one of the following is a strong base? A) Mg(OH)₂ B) Ca(OH)₂ C) NH₃ D) CH₃OH
There are 8 strong bases: LiOH, NaOH, KOH, RbOH, CsOH, Ca(OH)2, Sr(OH)2,and Ba(OH)
Which describes the entropy change in the reaction? 2 Cl₂O₇(g) → 2 Cl₂(g) + 7 O₂(g) A) The Δentropy is (-) b/c a larger molecule (Cl₂O₇) is converted into two smaller molecules (Cl₂ and O₂). B) The Δentropy is zero b/c the reactants and products are all gases. C) The Δentropy cannot be determined b/c the temp is not specified. D) The Δentropy is (-) b/c there are more moles of products than reactants. E) The Δentropy is (+) b/c there are more moles of products than reactants.
There are two moles of gaseous reactants and nine moles of gaseous products. This is an increase in the disorder of the system and would have a positive entropy change. E
Considering the redox reaction Cr + Ni²⁺ → Cr³⁺ + Ni, how many electrons are transferred in the balanced reaction?
To balance the charges in the equation CrCr must have a coefficient of 2 and Ni a coefficient of 3, 2 Cr + 3 Ni²⁺ → 2 Cr³⁺ + 3 Ni2 Cr + 3 Ni²⁺ → 2 Cr³⁺ + 3 Ni so a total of 6 electrons are transferred in the balanced reaction.
The pH of a basic solution is 8.11. What is [H⁺]?
To determine the concentration of H+ in the solution, use the relationship: [H+]=10^−pH So if the pH= 8.11, then [H+]=10^−8.11= 7.8×10−9M
Which equation is used to determine the amount of time required for the initial concentration to decrease by 45% if the rate constant has units of s⁻¹? A) t = ln 2/k B) Rate = k[A] C) ln([A]/[A]₀) = -kt D) [A] = [A]₀ - kt E) 1/[A] = 1/[A]₀ + kt
To determine the order, you should look at the units of the rate. It has units of s−1�−1, which indicates that it is a first order reaction. The equation for a first order rate law is: ln([A]/[A]₀) = -kt C
Consider the reaction: ICl(g) + Cl₂(g) → ICl₃(s). The ∆G(f)° of ICl(g) is -5.5 kJ/mol and the ∆G(f)° of ICl₃(s) is -22.59 kJ/mol What is the ∆G° of the reaction, in kJ/mol?
ΔG∘=ΣΔG∘f(products)−ΣΔG∘f(reactants) Remember, ΔG∘f of Cl₂ is 0. ΔG∘=−22.59kJmol−(−5.50kJmol)=−17.1kJmo
