Third Exam – Form D – Key 1. C 2. B 3. A 4. B 5. E 6. B 7. D 8. C 9. A 10. C 11. A 12. A 13. B 14. C 15. B 16. A 17. A 18. C 19. B 20. 3 mol 21. K2CO3(s)  2 K1+(aq) + CO32−(aq) 22. 1 mol1.75 g x 134.4 gM = 0.125 L 23. (not graded) −2000 J 24. a) 2 H2S(g) ⇄ 2 H2(g) + S2(g) b) CH4(g) ⇄ C(s) + 2 H2(g) 22 2 22[ H ] [ S ] K = [ H S ] 224[ H ]K = [ CH ]1. Select the true statement regarding cubic unit cells A) The simple cubic has the smallest number of atoms and greatest packing efficiency B) The simple cubic has the largest number of atoms and the least packing efficiency C) The face centered cubic has the largest number of atoms and the greatest packing efficiency D) The body centered cubic has the largest number of atoms and the greatest packing efficiency E) The face centered cubic has the smallest number of atoms and the least packing efficiency 2. The unit cell shown at the right is of the mineral Chromatite, which is made of chromium ions (white spheres) and oxide ions (black spheres). Note there is a black sphere on each face, and white spheres at the corners and in the body of the cell. What is the chemical formula of this compound? A) Cr3O2 B) Cr2O3 C) CrO D) Cr2O E) CrO2 3. In the diagram at the right, identify the conductor. 4. Note the following melting points (all of these elements are considered to be non-metals): SeC2 : 46 oC SiS2 : 1090 oC Ga2Se3 : 1020 oC Sb2S5 : 75 oC In their solid state, how many of these materials would be molecular solids? A) 1 B) 2 C) 3 D) 4 E) 0 5. Select the best statement regarding bonding between molecules or ions in solids: A) The bonding in covalent solids is much weaker than in molecular or ionic solids B) The bonding in ionic solids is much weaker than in covalent or molecular solids C) The bonding in covalent and ionic solids is much weaker than in molecular solids D) The bonding in covalent and molecular solids is much weaker than in ionic solids E) The bonding in molecular solids is much weaker than in covalent or ionic solids For the next two questions, consider the following materials: A) H2O B) F2 C) HF D) SiO2 E) CH3Cl 6. Select the material with the lowest melting point 7. Select the material with the highest melting point8. When water boils, A) the value of ∆H is negative and the value of ∆S is positive B) the value of ∆H is negative and the value of ∆S is negative C) the value of ∆H is positive and the value of ∆S is positive D) the value of ∆H is positive and the value of ∆S is negative 9. Select the FALSE statement concerning a system and its surroundings: A) When the system absorbs heat, ∆E of the system is negative B) When work is done by the system, ∆E of the surroundings is positive C) When the system releases heat, ∆E of the surroundings is positive D) When work is done on the system, ∆E of the system is positive 10. Consider the following reaction: NO2(g) + N2O(g)  3 NO(g) If this reaction is endothermic, what can you say about the spontaneity? A) The reaction is spontaneous at both low and high temperature B) The reaction is spontaneous at low temperature, but non-spontaneous at high temperature C) The reaction is non-spontaneous at low temperature, but spontaneous at high temperature D) The reaction is non-spontaneous at both low and high temperature 11. What is the difference between ∆G and ∆Go? A) ∆Go is for specific amounts of reactant and product, ∆G is for unspecified amounts B) for a given reaction, they will be of opposite signs C) ∆Go is specifically for 0 oC, ∆G is for unspecified temperature D) ∆G gives the spontaneity of a reaction, ∆Go does not E) ∆G includes entropy, ∆Go does not 12. Given this reaction: A(g) ⇄ B(g) If, starting with equal concentrations of A and B, the rate of the reverse reaction is greater than the rate of the forward reaction, then when the system reaches equilibrium: A) K < 1 B) K = 1 C) K > 1 13. Given this reaction: C(g) ⇄ D(g) If ∆Go is negative for this reaction, then: A) The activation energy for the forward reaction is larger than for the reverse reaction B) The activation energy for the forward reaction is smaller than for the reverse reaction C) The activation energy for the forward reaction is equal to that for the reverse reaction14. Given this reaction: E(g) ⇄ F(g) If the value of K is 0.01 for this reaction, then A) The value of ∆Go will be negative B) The value of ∆Go will be zero C) The value of ∆Go will be positive 15. Given the reaction energy diagram shown at the right, you can conclude that A) the reaction is exothermic, and increasing the temperature will increase the amount of product B) the reaction is exothermic, and increasing the temperature will increase the amount of reactant C) the reaction is endothermic, and increasing the temperature will increase the amount of product D) the reaction is endothermic, and increasing the temperature will increase the amount of reactant 16. Given the following reaction: CS2 + 4 H2 ⇄ CH4 + 2 H2S If H2S is removed from the system, you should expect: A) the amount of CH4 to increase and the amount of H2 to decrease B) the amount of CH4 to decrease and the amount of H2 to decrease C) the amount of CH4 to decrease and the amount of H2 to increase D) the amount of CH4 to increase and the amount of H2 to increase 17. During a reaction, a stronger bond breaks and a weaker bond forms. This reaction is most likely: A) endothermic B) exothermic Use the phase diagram of material X shown at the right to answer the following two questions. 18. At 50 oC and 0.2 atm pressure, X is a A) solid B) liquid C) gas D) supercritical fluid 19. At 40 oC, if the pressure is lowered from 0.4 atm to 0.1 atm, X will: A) melt B) sublime C) condense D) freeze E) boil GO ON TO THE NEXT PAGE PLACE YOUR ANSWERS FOR #20 – 24 DIRECTLY ON THIS EXAM P(atm)T (oC)10.4601805020. (8) Consider the following balanced equation: 2 C2H2 + 5 O2 → 4 CO2 + 2 H2O If 3 moles of C2H2 react with 10 moles of O2, how many moles of H2O can be formed? Answer : 21. (10) Write