Page 1 of 6 THE UNIVERSITY OF BRITISH COLUMBIA CHEM 154 Midterm Examination November 12, 2020 Time Limit: 60 minutes Total Marks: 45 Student Number: ___________________________ Name (printed): ____________________________ Please circle your lecture section 111 133 177 Signature: _________________________________ Examination Rules 1. You must leave your camera on throughout the examination procedure. You may be asked to hold up your UBC card for identification purposes, and an invigilator may also ask you to share your screen at any point during the exam. The camera feed will be recorded but only used should the need arise to deal with irregularities. Your privacy is important to us. 2. The invigilators will tell you when to start and stop writing the exam. Do not look at any exam questions until the start of the writing of the exam. 3. You must conduct yourself honestly, follow any rules or directions communicated by the invigilators, and stay in view of your camera the entire time the exam is being written. 4. You are not allowed to access a computer or any other electronic device from the time you receive the printed copy of the exam until the time you scan the exam for upload. You are not allowed to wear ear buds or headsets or any other such device but are allowed to wear standard ear plugs if you feel you wish to lessen any noise in your environment. 5. In addition to pens, pencils and erasers, you are allowed to have a scientific calculator and clock, as well as a molecular model kit, if desired. 6. Examination candidates suspected of any of the following, or any other similar practices, may be immediately dismissed from the examination by the examiner/invigilator, and may be subject to disciplinary action: i. purposely exposing written papers to the view of other examination candidates or imaging devices; ii. purposely viewing the written papers of other examination candidates; iii. using or having visible at the place of writing any books, papers or other memory aid devices other than those authorized by the examiner(s); iv. distributing in any manner, electronic or otherwise, copies of any part of the exam. 7. If a need arises to contact the invigilator, raise your hand for the invigilator to see on their display. Contact the invigilator for any issue arising during the exam, such as the need to go to the washroom or to report a technical problem. 8. Invigilators are instructed to not provide answers to any questions about the exam content, the interpretation of exam questions, or suspected errors in questions. If you suspect a question to have an error or ambiguity, detail this on your exam paper, and all such issues will be dealt with during the marking of the exam. 9. If you finish writing the exam before the allotted time, please wait in silence at your place of writing in full view of the camera until the allotted time has expired. 10. Under no circumstances should you exit the exam Zoom meeting unless directed to do so by an invigilator. Copyright © 2020 Department of Chemistry, The University of British Columbia. All rights reserved. Page 2 of 6 1. [9 marks total] You are an engineer on Mars charged with extracting water from the northern ice cap and building a pipeline to transport it back to a colony. Your pipeline will be wellinsulated and be able to carry liquids or gases. The colony environment is at 1 atm pressure and 25˚C but conditions at the northern ice cap are -150 ˚C and 600 Pa. You have access to industrial heaters and pumps. Phase Diagram of Water Data ΔHfus = 6.01 kJ/mol ΔHsub = 51.1 kJ/mol ΔHvap = 44.0 kJ/mol CP,m[H2O(l)] = 75.38 J/(mol K) CP,m[H2O(g)] = 36.57 J/(mol K) CP,m[H2O(s)] = 32.0 J/(mol K) (averaged for temp. range) a) Describe in words the process you will use to harvest and transport the water. Draw this process on the phase diagram to the right. Your description should include the phase of the water in each part of your process, the temperature and pressure of any phase changes, and the kind of phase change(s) that occur. b) Will the fluid in the pipeline be liquid or gas? Copyright © 2020 Department of Chemistry, The University of British Columbia. All rights reserved. Page 3 of 6 c) How much heat is required per mole to get the water into the pipeline? 2. [6 marks total] Consider the polymer shown in the reaction below. a) Draw the monomers that must react to produce the products shown. b) Is this polymer expected to be more or less stiff than high density polyethylene? Explain why. Copyright © 2020 Department of Chemistry, The University of British Columbia. All rights reserved. Page 4 of 6 3. [6 marks total] On the graph, sketch and label predictions for curves of PV/nRT versus density (at fixed T) for the gases He, CH4 and NH3. Briefly explain what causes the curves to have the shapes you’ve drawn. 4. [6 marks total] Consider the following reactions of ethyne: C2H2(g) + Cl2(g) → C2H2Cl2(l) C2H2(g) + 5/2 O2(g) → 2 CO2(g) + H2O(g) ΔH0 = -257.4 kJ ΔH0 = -1256.2 kJ Given ΔH0f [CO2(g)] = -393.5 kJ/mol and ΔH0f [H2O(g)] = -241.8 kJ/mol, find the enthalpy of formation for C2H2Cl2(l), in kJ/mol. Copyright © 2020 Department of Chemistry, The University of British Columbia. All rights reserved. Page 5 of 6 5. [6 marks total] Sodium hydrogen sulfite, NaHSO3, is added to wines to prevent oxidation and preserve flavor. a) Draw all valid Lewis structures that contribute to the resonance hybrid of the hydrogen sulfite anion,HSO− 3 , (H is bonded to O). Show all bonds as lines and lone pairs as dots; indicate formal charges and overall charges where applicable. b) Write the words “Least Contributor” directly beneath the structure that contributes the least to the resonance hybrid. Below, explain why that structure is the least contributor. 6. [6 marks totals] Complete the table by drawing for each molecule the best Lewis structure and a perspective diagram, as well as indicating whether it is polar. For the Lewis structure, show all bonds as lines and lone pairs as dots. Molecule Best Lewis Structure Perspective Diagram Polar ? (Yes/No) ClF5 SiCl2 F2 Copyright © 2020 Department of Chemistry, The University of British Columbia. All rights reserved. Page 6 of 6 7. [6 marks total] Use bond enthalpies to estimate ΔH0, in kJ, for the reaction: C2H2(g) + H2(g) → C2H4(g) Bond Enthalpies in kJ/mol C–C 350 C–H 410 C=C 611 C–O 350 C≡C 835 C–F 450 H–H 436 C–Cl 330 H–Cl 432 C–Br 270 H–Br 366 C–N 300 Complete the table to the right by indicating the signs of q and w when the reaction written above is performed at constant standard pressure. Briefly state the reasons for your choices. Quantity q w + or - ? Copyright © 2020 Department of Chemistry, The University of British Columbia. All rights reserved.
