Chemistry 155 - Problem set 1 Due on Gradescope by 5 PM on Monday Jan 8, 2024 Comments: This and all assignments contains several suggested book problems. These are for additional practice and should not be turned in. Answers to these problems will be posted along with the answers to the assigned problems. Problems sets should be uploaded to Gradescope by the date and time noted at the top of the problem set. Instructions for uploading files is on Canvas. The first four problems in this week’s assignment involve a review of 145 material. Warmup problems (will not be collected): Chapter 12: 12.2, 12.4, 12.8, 12.9, 12.10, 12.65 Assigned problems (turn in for a grade): 1. Based on the Ideal Gas law, a thermometer can be developed by keeping a gas at constant volume and monitoring the pressure changes as the temperature is increased. One such thermometer measures a pressure of 48.135 Torr at the triple point temperature of water (273.16 K). a. What change in pressure indicates a change in temperature of 1.00 K from 273.16 K to 274.16 K. b. Should this result change if you performed this calculation at another temperature? Why or why not. If you are not sure, you can check your answer by doing the calculation, but you don’t need to. 2. A vessel with a volume of 22.4 L contains 2.00 mol of H2 and 1.00 mol of N2 at 273.15 K. All of the hydrogen is reacted to form ammonia. a. What is the pressure of the gases in this vessel prior to reaction? b. Assuming the temperature and volume are not changed in the reaction, what are the partial pressures of the gases present following reaction? 3. A 2.747-g sample of manganese metal is reacted with excess HCl(aq) to produce 1.61 L of H2(g) at 373 K and 0.951 atm as well as a manganese chloride compound (MnClx). a. What is the formula of the manganese chloride compound that is produced in this reaction? b. Write a balanced chemical equation for this process. c. Calculate the work (in kJ) done by this reaction (note the initial volume may be taken to be zero, so the change in volume will be the volume of H2 gas that is formed). d. Calculate Δ𝑈 in kJ per mole of magnesium reacted based on the reaction in part b. The heat generated by this reaction is -24.06 kJ. 4. The specific heat capacities of halogens in the gas phase and in their natural occurring phase at room temperature are provided in the table below. A Jupyter notebook has been provided to assist with this problem. You should turn in your answers to this question as a Jupyter notebook. There will be a separate assignment Gradescope for you to turn in this problem. Element Fluorine Chlorine Bromine Iodine Specific heat (gas) (/J g-1 K-1) 0.824 0.478 0.225 0.145 Specific heat naturally occurring phase at 298 K 0.824 0.478 0.474 0.427 a. Use these values to evaluate the molar heat capacities in J mol-1 K-1 for these elements. b. Identify any periodic trend and, if identified, show a fit of your data. A Jupyter notebook has been provided to assist with this. You should turn in the Jupyter notebook as a separate assignment on Gradescope. c. Use the data obtained in part (b) predict the molar heat capacity of astatine, At2(g) [answer in Jupyter notebook]. d. How does this value compare to the expected value for the heat capacity of roughly 4.5 R, where R is the ideal gas constant? 5. Consider the three types of systems that we discussed in class a. Provide a brief description of the defining characteristics of open, closed, and isolated systems. b. The text mentions three types of walls (or boundaries between the system and the surrounding: rigid, adiabatic and diathermal walls. For each of the systems provided in part (a), what type of walls would be consistent with your description. c. Provide two ways you could increase the internal energy of i. An open system ii. A closed system 6. For each of the following situations, indicate if the indicated property is positive, negative or zero, or cannot be determined based on the information provided. Provide a brief justification for your answer. a. For an adiabatic expansion in a closed system: i. q ii. w iii. Δ𝑈 b. Heat a rigid closed system i. q ii. w iii. Δ𝑈 7. A 100.-W electric heater (1 W = 1 J s-1) operates for 15.0 minutes to heat an ideal gas sample in a cylinder. At the same time the gas sample expands from 2.00 to 8.00 L against a constant pressure of 0.978 atm. a. What are the signs of q and w for this process (no math is needed) b. Calculate the change in the internal energy of the gas.
