Thermodynamics
Kinetics
Acids/Bases
Electrochemistry
Equilibiurm
100
C(s) + O2(g) -> CO2(g) dH= -200.0 kJ H2(g) + (1/2)O2(g) -> H2O(l) dH= -347 kJ C2H2(g) + (5/2)O2(g) -> 2CO2(g) + H2O(l) dH= -1162 kJ Find the enthalpy change for: 2C = H2(g) -> C2H2(g) a) 415 b) 500 c) 378 d) 488 e) 299
What is Answer: a) 2[C(s) + O2(g) -> CO2(g)] 2(-200.0kJ) H2(g) +(1/2)O2(g) -> H2O(l) -347kJ 2 CO2(g) + H2O(l) -> C2H2(g) + (5/2)O2(g) +1162kJ 2C(s) + H2(g) -> C2H2(g) = 415kJ
100
The slow rate of a particular chemical reaction might be attributed to which of the following? I. a low activation energy II. a high activation energy III. the presence of a catalyst IV. the temperature is low V. the concentration of the reactants are high a) V. only b) I., III., and IV. only c) II. and IV. only d)I. and IV. only e) All can be causes.
What is Answer: c) Because high activation energies cause slow reactions, due to the fact that they take more time in releasing their bonds (which are often stronger), while low temperatures provide little availible energy needed for a reaction to occur.
100
Sodium Hydroxide is a strong base, this means that….. a) Aqueous solutions of NaOH contain equal concentrations of H+(aq) and OH-(aq). b) NaOH does not dissociate at all when it is dissolved in water, c) NaOH dissociates completely by Na+(aq) and OH-(aq) when it dissolves in water d) NaOH cannot be neutralized by a weak acid. e) NaOH cannot be neutralized by ordinary means.
What is Answer: c) When ever a strong base or acid mixes with water, they completely dissociate into their separate elements.
100
In the electrolytic decomposition of water:??2H2O → 2H2 + O2 a) Hydrogen is formed at the cathode and oxygen is formed at the anode. b) Hydrogen is formed at both the anode and the cathode. c) Oxygen is formed at both the anode and the cathode. d) Hydrogen is formed at the anode and oxygen is formed at the cathode. e) Neither are formed anywhere.
What is Answer: a) The H is the positive element, making it the cathode, while the O is the negative element, making it the anode.
100
In another experiment involving the above reaction (the last question) at 1000 degrees celsius, the equilibrium concentrations were found to be??[H2]=2.0 moles per liter?[CO2]= 5.0 moles per liter?[H2O]= 4.0 moles per liter?[CO]= 4.0 moles per liter ??What is the equilibrium constant, K, for this reaction?? a)0.40? b)0.63? c)0.005? d)1.6? e)3.8?
What is Answer: d) H2]=2.0 mol/L?[CO2]= 5.0 mol/L?[H2O]= 4.0 mol/L?[CO]= 4.0 mol/L??K = [H2O][CO] / [H2][CO2]?K = (4.0)(4.0) / (2.0)(5.0)?K = 1.6
200
Two solutions, both at the same temperature, are mixed. After mixing the temperature drops dramatically. Which of the following statements is/are true? I. Products have stronger bonds (lower enthalpy) than reactants. II. Products have weaker bonds (higher enthalpy) than reactants. III. Products are more stable than reactants. IV. Products are less stable than reactants. a) I only b) IV only c) I & III only d) II & IV only e) All are false
What is Answer: d) Because, the temperature drops after mixing, showing how heat is being absorbed making the reaction endothermic. Therefore, the products have weaker bonds (higher enthalpy) than the reactants and shows how the products are less stable than the reactants.
200
A reaction follows the rate law: Rate = k[A]2. Which of the following plots will give a straight line? a) 1/[A] versus 1/time b) [A]2 versus time c) 1/[A] versus time d) ln[A] versus time e) [A] versus time
What is Answer: c) The "2" exponent means this is a second-order rate law. Second-order rate laws give a straight-line plot for 1/[A] versus t.
200
The net ionic equation for the reaction that occurs during the titration of nitrous acid with sodium hy¬droxide is a) HNO2 + Na+ + OH– -> NaNO2 + H2O b) HNO2 + NaOH -> Na+ + NO2– + H2O c) H+ + OH– ->H2O d) HNO2 + H2O -> NO2– + H3O+ e) HNO2 + OH– -> NO2– + H2O
What is Answer: e) Becuase, all the other choices have the incorrect compounds present or have seperate elements when they should be compounds.
200
The equation that represents a reaction that is not a redox reaction is:??1. 2H2 + O2 → 2H2O??2. Zn + CuSO4 → ZnSO4 + Cu??3. 2H2O2 → 2H2O + O2??4. H2O + CO2 → H2CO3? a) All of these are redox reactions b) Reaction 4 c) Reaction 2 d) Reaction 3 e) Reaction 1
What is Answer: b) The charges for the products and the reactants for H2O + CO2 → H2CO3 are the same, showing how it is not a redox reaction; because a redox reaction contains an element being oxidized and one being reduced.
200
A 0.1-molar solution of acetic acid (CH3COOH) has a pH of about a) 1 b) 3 c) 7 d) 10 e) 14
What is Answer: b) An acid, any acid, will give a pH below 7; thus, answers C–E are eliminated. A 0.1-molar solution of a strong acid would have a pH of 1. Acetic acid is not a strong acid, so answer A is eliminated.
300
A reaction occurs that has both a positive delta S and a positive delta H value, from this information it can be concluded that the reaction…. a) Can be spontaneous at any temperature. b) Cannot be spontaneous at any temperature. c) Cannot be spontaneous at high temperatures. d) Can be spontaneous at only high temperatures. e) Can be spontaneous at only low temperatures.
What is Answer: d) At higher temperatures the amount of T delta S is high and can overcome the amount of a positive delta H in the equation dG= dH-TdS, making the reaction spontaneous.
300
The steps below represent a proposed mechanism for the catalyzed oxidation of CO by O3. Step 1: NO2(g) + CO(g) → NO(g) + CO2(g) Step 2: NO(g) + O3(g) → NO2(g) + O2(g) What are the overall products of the catalyzed reaction? a) CO2 and O2 b) NO and CO2 c) NO2 and O2 d) NO and O2 e) NO2 and CO2
What is Answer: a) Add the two equations together: NO2(g) + CO(g) + NO(g) + O3(g) → NO(g) + CO2(g) + NO2(g) + O2(g) Then cancel identical species that appear on opposite sides: CO(g) + O3(g) → CO2(g) + O2(g)
300
A solution of HCl and a solution of NaOH are titrated together to find the concentration of the HCl. The NaOH has a concentration of 2 and a volume of 15ml is used to turn the solution a light pink due to the presence of phenolphthalein. What is the concentration of the HCl if 10ml of it is used in the solution? a) 5 b) 3 c) 2.5 d) 8.79 e) 1.4
What is Answer: b) MaxVa = MbxVb; Ma= MbxVb=15x2=3 as the concentration of HCl. Va 10
300
In the reaction below, the oxidizing agent is:??2NaCl + 2H2SO4 + MnO2 → Na2SO4 + MnSO4 + 2H2O + Cl2 a) H+ b) Cl- c) Na+ d) Mn4+ e) O2-
What is Answer: d) Mn4+ Because, Mn goes from having a charge of +4 to a charge of +2, showing a gain of electrons.
300
For which of the following reactions will a reduction in volume NOT affect the equilibrium position? a) H2(g) + Cl2(g) <--> 2HCl(g) b) 2SO3(g) <--> 2SO2(g) + O2(g) c) N2O4(g) <--> 2NO2(g) d) C(s) + CO2(g) <--> 2CO(g)
What is Answer: a) Because, the reactant is a compound formed from the existing elements; so even with volume reduced the amount of reactant would be the same.
400
Which of the following are not exothermic? a) Combustion of butane.  b) Melting copper.  c) Freezing water.  d) Condensing steam. e) Sublimation of nitrogen
What is Answer: b) The Copper is going from a solid state to a liquid state, causing it to absorb energy (which is endothermic) in order for it to occur.
400
The mechanism below has been proposed for the reaction of CHCl3 with Cl2. Step l: Cl2 2 Cl(g) fast Step 2: Cl(g) + CHCl3(g) → CCl3(g) + HCl(g) slow Step 3: CCl3(g) + Cl(g) → CCl4(g) fast Which of the following rate laws is consistent with this mechanism? a) Rate = k[Cl2] b) Rate = k[CHCl3][Cl2] c) Rate = k[CHCl3] d) Rate = k[CHCl3]/[Cl2] e) Rate = k[CHCl3][Cl2]1/2
What is Answer: e) The rate law depends on the slow step of the mechanism. The reactants in the slow step are Cl and CHCl3 (one of each). The rate law is first order with respect to each of these. The Cl is half of the original reactant molecule Cl2. This replaces the [Cl] in the rate law with [Cl2]1/2.
400
Which of the following ions is the strongest Lewis acid? a) Na+ b) Cl– c) CH3COO– d) Mg2+ e) Al3+
What is Answer: e)
400
A sample of silver is to be purified by electrorefining. This will separate the silver from an impurity of gold. The impure silver is made into an electrode. Which of the following is the best way to set up the electrolytic cell? a) An impure silver cathode and an inert anode. b) An impure silver cathode and a pure gold anode. c) A pure silver cathode with an impure silver anode. d) A pure gold cathode with an impure silver anode. e) An impure silver cathode with a pure silver anode.
What is Answer: c) The impure silver must be oxidized so it will go into solution. Oxidation occurs at the anode. Reduction is required to convert the silver ions to pure silver. Reduction occurs at the cathode. The cathode must be pure silver, otherwise it could be contaminated with the cathode material.
400
2 SO3(g) ⇄ 2 SO2(g) + O2(g) After the equilibrium represented above is established, some pure O2(g) is injected into the reaction vessel at constant temperature. After equilibrium is reestablished, which of the following has a lower value compared to its value at the original equilibrium? a) Keq for the reaction b) The total pressure in the reaction vessel c) The amount of SO3(g) in the reaction vessel d) The amount of O2(g) in the reaction vessel e) The amount of SO2(g) in the reaction vessel
What is Answer: e) Because due to the increase in the amount of O2, less SO2 is formed from the SO3 in order to maintain equilibrium.
500
Which statement about the vaporization of acetone, CH3COCH3, is not correct ?    a) When acetone vaporizes, covalent bonds are broken.  b) The vaporization of acetone is the reverse process of condensation.  c) The vaporization of acetone is an endothermic process.  d) When acetone vaporizes, intermolecular interactions are overcome. e) Condensation is the reverse process of vaporization
What is Answer: a) The only change occurring for CH3COCH3 is a change in state of matter, it is not breaking apart therefore the bonds are not broken.
500
The reaction (CH3)3CBr(aq) + H2O(l) → (CH3)3COH(aq) + HBr(aq) follows the rate law: Rate = k[(CH3)3CBr]. What will be the effect of decreasing the concentration of (CH3)3CBr? a) The rate of the reaction will increase. b) More HBr will form. c) The rate of the reaction will decrease. d) The reaction will shift to the left. e) The equilibrium constant will increase.
What is Answer: c) The compound appears in the rate law, and so a change in its concentration will change the rate. The reaction is first order in (CH3)3CBr, so the rate will change directly with the change in concentration of this reactant. There is no equilibrium arrow, so the reaction is not in equilibrium. If the reaction were in equilibrium, d) would also be true.
500
All of the following experimental procedures will produce buffers, except one. Which procedure fails to yield a buffer solution? a) Mixing solutions ammonia and ammonium bromide. b) Mixing solutions of propanoic acid and potassium propanoate. c) Mixing solutions of nitric acid and potassium nitrate. d) Mixing solutions of butanoic acid and sodium butanoate. e) Partially reacting a weak acid with a strong base, ensuring that some of the weak acid remains in excess.
What is Answer: c) Because nitric acid is a strong acid
500
When a basic solution of KMnO4 is added to an SnCl2 solution, a brown precipitate of MnO2 forms and Sn4+ remains in solution. When the same basic solution of KMnO4 is added to an NaF solution, no reaction occurs. Which of the substances involved in these reactions serves as the best reducing agent? a)SnCl2 b) KMnO4 c) NaF d) MnO2 e) Sn4+
What is Answer: a) The Sn2+, from SnCl2, reduces the manganese from +7 to +4. This makes SnCl2 a reducing agent. The tin is oxidized to Sn4+, so KMnO4 is an oxidizing agent. NaF did nothing, so it behaves as neither an oxidizing nor as a reducing agent.
500
H2(g) + CO2(g) + 10kcal---->H2O(g) +CO(g)???3.0 moles of H2 (g) , and 4.5 moles of CO2 (g) are placed in an empty reaction vessel and the temperature is maintained at 1000 degrees Celsius as the reaction is allowed to come to equilibrium. After the equilibrium has been established, an analysis of the equilibrium mixture indicates that 2.0 moles of CO(g) and 2.0 moles of H2O(g) have been found. How much hydrogen, H2(g), is present at equilibrium??? a)1.0 mole? b)1.5 moles? c) 2.0 moles? d) 2.5 moles? e) 3.0 moles ?
What is Answer: a)??H2(g) + CO2(g) ----> H2O(g) + CO(g)??Initially:?mole of H2 = 3.0 mol?mole of CO2 = 4.5 mol?mole of H2O and CO = 0+2.0=2.0 mol??Equilibrium:?mole of H2 = 3.0 - 2.0 = 1.0 mol?mole of CO2 = 4.5 - 2.0 = 2.5 mol?mole of H2O and CO = 2.0 mol
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