Discussion Section Worksheet, General Chemistry II | CHEM 104, Exams of Chemistry

Download Discussion Section Worksheet, General Chemistry II | CHEM 104 and more Exams Chemistry in PDF only on Docsity! Chemistry 104 A/D Discussion Section Worksheet Discussion Section #5 Key Ideas from Lecture #5: q = -q: Let’s review constant pressure calorimetry using a heating curve: Constant volume calorimetry: Hess’s Law: Let’s think about these concepts for a bit... In this class we have looked at both constant pressure and constant volume calorimetry. What values do these different forms of calorimetry allow us to determine? In what type of reactions are the values of ΔH and ΔE closest to each other? Why would you want to use one type of calorimetry over another experimentally? For these questions, it may be helpful to consider the equations: ΔE = q + w w = - Pext ΔV ΔH = q (constant pressure) Problems: Hour Exam I, Spring 2007, #12 You completely combust one (1) piece of paper in a bomb calorimeter (C = 6.93 kJ/ oC) and find that the temperature of the bomb apparatus increases by 71.4 oC. You look up the ΔE of combustion for paper and find that ΔEcomb = -2787 kJ/mol. How much did the sheet of paper weigh (assuming a MW of paper of 180.18 g/mol)? Stuck? First, try to understand what the problem is asking for. Next, list all the important information that you know (including equations that may be useful). Try to determine the best way for you to solve the problem, then solve the problem. Does the answer make sense? Start by looking at Sample Exercise 6.6 and the proceeding discussion (pg 242 of Zumdahl). Next, use dimensional analysis to work from the heat evolved from burning the sheet of paper to the mols of paper, and then finally the mass of the paper. Make sure to pay attention to your units! 1 Chemistry 104 A/D Discussion Section Worksheet Discussion Section #5 Hour Exam I, Spring 2008, #12 Consider the following reaction for this problem, which is similar to a lab experiment you all have performed: 2 HCl (aq) + Ba(OH)2 (aq) BaCl2(aq) + 2 H2O (l) ΔHrxn = -118 kJ You are performing a calorimetry experiment where you add 80 mL HCL (0.01 M at 25 oC) to 50 mL (0.1 M at 25 oC). You are asked to determine the final temperature of the solution. You can assume that there is no heat loss to the surroundings, the density of the solution is 1 g/mL, and that the specific heat capacity of the solution is 3.867 gC J o . Stuck? First, try to understand what the problem is asking for. Next, list all the important information that you know (including equations that may be useful). Try to determine the best way for you to solve the problem, then solve the problem. Does the answer make sense? Start by determining the limiting reagent for the reaction. Next, what is gaining heat and what is losing heat (there are two “things” to think about here: the reaction that is creating the flow of heat, and where the heat is flowing to/from). Next, determine how much heat the reaction will give off (Sample Exercise 6.4, page 236 of Zumdahl). Finally, solve for the final temperature using the equations q = -q and q = m c ΔT. Make sure to pay attention to your units! Hour Exam I, Fall 2006, #7 A 5.36 g sample of ammonium nitrate (MW = 80.05 g/mol) was dissolved in 72.0 g of water that was inside of a coffee-cup calorimeter. After the ammonium nitrate was fully dissolved the temperature of the solution had decreased from 26.2 oC to 14.3 oC. Calculate ΔH for the process of dissolving 1 mol of ammonium nitrate. (Assume the specific heat of water and the solution are 4.184 J/g oC). NH4NO3 (s) + H2O (l) NH4+ (aq) + NO3- (aq) + H2O (l) ΔHrxn = ? Stuck? First, try to understand what the problem is asking for. Next, list all the important information that you know (including equations that may be useful). Try to determine the best way for you to solve the problem, then solve the problem. Does the answer make sense? Start by determining what is gaining heat and what is losing heat (q = -q). Next, determine the value of q for the solution (use q = m c ΔT). At this point you should be able to know the value of q for the reaction, but that is only for a 5.36 g sample of the NH4NO3. To determine the value of ΔHrxn for the dissolution of NH4NO3, convert the value of q into J/mol. Make sure to pay attention to your units! 2