21. The U-238 nucleus decays to form Pb-206 by α and β decays. Calculate the number of α decays.
(A)2
(B)4
(C) 6
(D)8
(E) none of these

1. Which of the experiments listed below did not provide the information stated about the nature of the atom? (A)The Rutherford experiment proved that the Thomson "plum pudding" model of the atom was essentially correct. (B) The Rutherford experiment determined the charge on the nucleus. (C) The cathode-ray tube proved that electrons have a negative charge. (D)Millikan's oil-drop experiment showed that the charge on any particle was a simple multiple of the charge on the electron. (E) none of these

2. The limiting reactant in a reaction (A)is the reactant for which you have the least number of moles. (B) has the lowest coefficient in a balanced equation. (C) has the lowest ratio of coefficient in the balanced equation to moles available. (D)has the lowest ratio of moles available to coefficient in the balanced equation. (E) none of these

3. A solution contains the ions Ag+, Pb2+, and Ni2+. Dilute solutions of NaCl, Na2SO4, and Na2S are available to separate the positive ions from each other. In order to effect separation, the solutions should be added in which order? (A)Na2S, NaCl, Na2SO4 (B) Na2SO4, NaCl, Na2S (C) Na2SO4, Na2S, NaCl (D)NaCl, Na2S, Na2SO4 (E) NaCl, Na2SO4, Na2S

4. Consider three 1-L flasks at the same temperature and pressure. Flask A contains CO gas, flask B contains N2 gas, and flask C contains O2 gas.In which flask do the molecules have the greatest momentum per impact? (A)The molecules in all the flasks have the same momentum per impact. (B) The molecules in two of the flasks have the same momentum per impact. (C) flask C (D)flask A (E) flask B

5. Consider the following equilibrium:N2(g) + 3H2(g) ⇄ 2NH3(g)with K = 2.3 × 10-6. 1.00 mol each of all reactants and products is placed in a 1.00-L container. Which way will the reaction initially proceed? (A)To the right. (B) We need to know the temperature. (C) The system is at equilibrium. (D)To the left. (E) none of these

6. As water is heated, its pH decreases. This means that (A)[OH-] > [H+]. (B) [H+] >[OH-]. (C) the water is no longer neutral. (D)Two of these are correct. (E) None of these is correct.

7. The reaction Cr(s) + NO3¯(aq) → Cr3+(aq) + NO(g) takes place in acidic solution.What is the coefficient of H2O(l) in the balanced equation? (A)3 (B) 5 (C) 4 (D)2 (E) 1

8. For a particular process q = -10 kJ and w = 25 kJ. Which of the following statements is true? (A)The system does work on the surroundings. (B) Heat flows from the surroundings to the system (C) ΔE = −35 kJ (D)All of these are true. (E) None of these is true.

9. For the reaction H2O(l) → H2O(g) at 298 K, 1.0 atm, ΔH is more positive than ΔE by 2.5 kJ/mol.This quantity of energy can be considered to be (A)the heat flow required to maintain a constant temperature. (B) the work done in pushing back the atmosphere. (C) the difference in the H—O bond energy in H2O(l) compared to H2O(g) (D)the value of ΔH itself. (E) none of these

10. Choose the correct statement. (A)A reaction that exhibits a negative value of ΔS cannot be spontaneous. (B) Exothermic reactions are always spontaneous. (C) Free energy is independent of temperature. (D)At constant pressure and temperature, a decrease in free energy ensures an increase in the entropy of the system (E) none of these

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