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# rvw3 - Exam 3 Review Sheet Exam 3 covers Chapter 6.3-end Ch...

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Exam 3 Review Sheet Exam 3 covers Chapter 6.3-end Ch. 6, Ch 7, and Ch 8 – 8.4 (Based on our expected coverage.) This review sheet is meant to be used after you have worked the problems suggested in your textbook and worked the old exam available at http://www-class.unl.edu/chem109/tests.htm Do NOT just study old exams! Suggested ways to work this review sheet: Review the problems given from previous exams. If you find difficulty working those, work similar problems that have answers given. Alternatively, you can work all problems on the review sheet. **Advice: Before putting things in your N-space, decide everything you want to put into it, trace the space onto another sheet of paper and write everything in – then you will know how large or small to write. All N-space suggestions are equations or diagrams we have discussed and I would think are useful. You may feel there are fewer or more items needed for your own sheet. Chapter 6.3-end: Calorimetry and Enthalpy (Thermodynamics) N-Space Suggestions: q = mc T ; q = nC T ; q cal = C cal T ; (know what each symbol stands for!) –q sys = q sur ; H f requires one mole product, reactants are elements in natural state, at STP ; H rxn = Σ(∆ H products ) - Σ(∆ H reactants ) Problems: 1. I gave you 4 pages of calorimetry and enthalpy questions in a handout posted on blackboard. Do those! 2. Using Hess’s Law and these three reactions (x, y, and z), (x) C (graphite) + O 2(g) CO 2(g) H x = -395.5 kJ (y) S (rhombic) + O 2(g) SO 2(g) H y = -296.1 kJ (z) CS 2(l) + 3O 2(g) CO 2(g) + 2 SO 2(g) H z = -1072.0 kJ determine the enthalpy change for the reaction, C (graphite) + 2S (rhombic) CS 2(l). (84.3 kJ) 3. Circle any of the following chemical equations for which H 0 rxn = H 0 f . a) ½ C (graphite) + S (rhombic) ½ CS 2(l). b) C (graphite) + O 2(g) CO 2(g)

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c) 2CaCO 3(s) 2Ca (s) + 3O 2(g) + 2C (s) d) 4NH 3(g) + 7O 2(g) 4NO 2(g) + 6H 2 O (g) e) CaCO 3(s) Ca (s) + 3/2 O 2(g) + C (s) 4. Calculate the enthalpy change for this reaction using standard enthalpies of formation. 4 NH 3(g) + 7 O 2(g) 4 NO 2(g) + 6 H 2 O (g) (-1130.2 kJ) 5. Next to each of the following reactions, write (a), (b), or (c). (a)= Work done by system on surroundings. (b)= Work done by surroundings on system. (c) = No work is done. (i) CaCO 3(s) CaO (s) + O 2(g) (ii) CS 2(l) + 3O 2(g) CO 2(g) + 2 SO 2(g) (iii) C (solid, graphite) + O 2(g) CO 2(g) (iv) H 2 O (g) H 2 O (l) (v) CO 2(s) CO 2(g) (i. a; ii. c; iii. c; iv. b ; v. a) 6. Interesting Questions Concerning Heat from http://hyperphysics.phy- astr.gsu.edu/hbase/thermo/heatques.html#c1 Think about them, then visit to find out answers. How is it that you can have both water and ice at 0 C and both water and steam at 100 C? A lot of energy goes into these phase transitions. Why doesn't it change the temperature? If you have steel and wood at 0 C, which feels colder? If you have steel and wood at 100 C, which feels hotter?
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