KEY 2023 CHM1311 F Midterm 1

CHM1311 Midterm 1 2023 Page 3 of 10 1. Short Answer Questions. a) (1 pt) Which of the following contains the greatest number of atoms? £ 1 g of He £ 1 g of C £ 1 g of U £ All contain an equal number of atoms b) (1 pt) Select one of the following compounds ( circle your choice ) and provide its formula. magnesium sulfite chromium (III) bromide perchloric acid Formula : _______________________ c) (1 pt) The figure on the right shows 1 mol of gas in an open- end manometer. What is the pressure of the gas in the flask (in mmHg) if the lab barometer reads 765.2 mmHg? £ 766.5 mmHg £ 763.9 mmHg £ 752.2 mmHg £ 778.2 mmHg d) (0.5 pt) Isotopes of an element always have the same number of neutrons. True False e) (1 pt) Place the following species in order of increasing oxidation state of C: CO 2 CH 4 CO C 2 O 4 2– _________ < _________ < _________ < __________ f) (1 pt) A gas, while expanding, absorbs 25 J of heat and does 215 J of work. Which of the following statements is correct? £ internal energy of the system increases , internal energy of the surroundings increases £ internal energy of the system decreases , internal energy of the surroundings decreases £ internal energy of the system increases , internal energy of the surroundings decreases £ internal energy of the system decreases , internal energy of the surroundings increases

CHM1311 Midterm 1 2023 Page 4 of 10 g) (1.5 pts) Match the three gases shown with the expected molecular speed distribution diagrams (A, B, C) at right. h) (1 pt) A toothpaste contains 0.55% m/v sodium fluoride. This concentration expressed in mol/L is: BONUS - For the hypothetical reaction below, carried out under constant pressure conditions, which of the following are correct? Circle all that apply. ∆ H > 0 W > 0 ∆ U = q + W ∆ H < 0 W < 0 ∆ U > 0 ∆ H » 0 W » 0 ∆ U < 0 A ( s ) à A ( l ) NUMBER OF MOLECULES ROOT-MEAN-SQUARED SPEED A B C ________ N 2 at 0ºC ________ O 2 at 0ºC ________ N 2 at 25ºC

CHM1311 Midterm 1 2023 Page 6 of 10 3. (6 pts) Consider two gas bulbs of equal volume, one filled with H 2 gas at 0ºC and 2 bar and the other containing O 2 gas at 25ºC and 1 bar. Answer the questions below by circling your answer. Show your work to earn full points. a) Which bulb has more molecules? H 2 O 2 b) Which bulb has more mass? H 2 O 2 c) Which bulb has a higher average kinetic energy? H 2 O 2 d) Which bulb has higher average molecular speed? H 2 O 2

CHM1311 Midterm 1 2023 Page 7 of 10 4. Carbon monoxide can be further oxidized to carbon dioxide according to the reaction: CO( g ) + ½ O 2 ( g ) à CO 2 ( g ) ∆ Hº = –283.0 kJ/mol a) (2 pts) How much heat, in kJ, is associated with the reaction of 10.0 grams of CO? b) (4 pts) What is the change in internal energy for the reaction of 10.0 g of CO at 298 K under constant pressure conditions? You may assume an exact stoichiometric quantity of oxygen is present. c) (2 pts) Using the template at right, draw a representative energy diagram for this reaction. Fully label your diagram, including: ∆ U, U 1 , U 2 , q p , and W. ENERGY

CHM1311 Midterm 1 2023 Page 9 of 10 6. The gaseous product of a chemical reaction is a chloride oxide that was bubbled through water and trapped in a tube. The volume of the trapped gas was 37.0 mL at 298 with a pressure of 754.0 mmHg. The vapour pressure of water at 298 K is 23.9 mmHg. a) (3 pts) Calculate the number of moles of chloride oxide that was produced. b) (3 pts) Combustion analysis shows the chloride oxide product contains 42.55% chlorine by mass (the rest is oxygen). What is the empirical formula of the chloride oxide? c) (3 pts) Determine the molecular formula of the compound, given that the mass of the chloride oxide product obtained in the above reaction was 235 mg.