chem test1 - Version 028 Exam 1 fakhreddine(51615 This...

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Version 028 – Exam 1 – fakhreddine – (51615) 1 This print-out should have 27 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0points The vapor pressure of water above 40 mL of water in a 100 mL container is 23.8 torr at 25 C. What is the vapor pressure of the water if the volume of the container is changed to 50 mL? 1. 11.9 torr 2. about 20 torr 3. 47.6 torr 4. about 25 torr 5. 23.8 torr correct Explanation: Vapor pressure is the pressure exerted by a vapor that exists in equilibrium with the liquid of the substance in question. As long as there is some liquid, the actual amount of liquid is irrelevant; the vapor pressure does not change. (Temperature affects vapor pres- sure.) 002 10.0points Based on the types and strengths of in- termolecular forces present, place the com- pounds C 6 H 14 , C 3 H 8 , C 5 H 11 OH , C 5 H 11 Cl , CaBr 2 in order from lowest to highest boiling point (lowest on the left, highest on the right). 1. CaBr 2 , C 5 H 11 OH , C 5 H 11 Cl , C 6 H 14 , C 3 H 8 2. C 6 H 14 , C 3 H 8 , C 5 H 11 OH , C 5 H 11 Cl , CaBr 2 3. C 3 H 8 , C 6 H 14 , C 5 H 11 OH , C 5 H 11 Cl , CaBr 2 4. CaBr 2 , C 5 H 11 Cl , C 6 H 14 , C 5 H 11 OH , C 3 H 8 5. C 3 H 8 , C 5 H 11 OH , C 6 H 14 , C 5 H 11 Cl , CaBr 2 6. C 3 H 8 , C 6 H 14 , C 5 H 11 Cl , C 5 H 11 OH , CaBr 2 correct Explanation: C 3 H 8 and C 6 H 14 have only dispersion forces, the weakest type of intermolecular forces. C 6 H 14 has a higher molecular weight and will therefore have stronger dispersion forces. C 4 H 11 Cl and C 5 H 11 OH are both approx- imately the same size as C 6 H 14 and would therefore have about the same strength of dis- persion forces. C 4 H 11 Cl also has dipole-dipole interactions, stronger than dispersion forces. C 5 H 11 OH also has H - bonding, stronger than dipole-dipole interactions. CaBr 2 is ionic and has interionic forces, the strongest type of intermolecular forces. The stronger the intermolecular forces, the higher the boiling point. 003 10.0points A dissolution process is exothermic if the amount of energy released in bringing about ? interactions is greater than the sum of the amounts of energy absorbed in overcom- ing ? and ? interactions. 1. solvent-solute; solute-solute; crystal lat- tice 2. solute-solute; crystal lattice; solvent- solvent 3. solvent-solvent; solute-solute; solvent- solute 4. solute-solute; solvent-solvent; solvent- solute 5. solvent-solute; solute-solute; solvent- solvent correct
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Version 028 – Exam 1 – fakhreddine – (51615) 2 Explanation: In the course of dissolution, you disrupt solute-solute interactions and solvent-solvent interactions in order to create new solvent- solute interactions. So you can imagine that you have to invest energy to break up solute- solute interactions and solvent-solvent inter- actions. However, you get energy back in the creation of solvent-solute interactions. If your investment in solute-solute and solvent- solvent interactions is less than your return in solvent-solute interactions, excess energy (as heat) will be produced and the reaction will be exothermic.
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