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The key concepts of chapter 5 in a college-level thermochemistry course. Class period assignments, problem sets, and answers. Topics covered include relative enthalpies, thermochemical equations, heat flow, specific heat, and calculating heat for a reaction. Students are expected to skim certain sections for background knowledge but will not be tested on them.
Typology: Assignments
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CH 221--Ziegler
Class period 1 -- Reading pp. 153-155(b); 155b-156m; 156m-158 (m); 158m- 164.
Class period 2 -- Reading pp. 166 – 171.
Class period 3 -- Reading pp. 174-180; 300(m) to 303(b).
Skim the pages marked with highlighter, for meaning, but don’t worry about being tested on these topics.
Answers to problems:
E (^) ZnCO 3 (s)
ZnO (s) + CO 2 (g)
5.30 ZnCO 3 (s) Æ ZnO(s) + CO 2 (g) ∆H = 71.5 kJ 71.5 kJ 5.33 See Text A- 5.34 a) heat is absorbed. b) 4.54 x 10^3 kJ c) 2.82 g H 2 d) ∆H = -90.7 kJ for the reverse reaction; and when 32.0 g CO reacts by this reverse reaction, the change in heat is -104 kJ (heat is released).
5.44 a) A transferred more heat to the water than B did, so its capacity to hold heat is greater, and its heat capacity is greater. b) Unless you know how much A and B weighed, you can’t express its specific heat capacity, which is usually given in units of J/g°C or J/gK.
5.46 a) 75.4 J/mol°C b) 634.9 J/°C, 506 kJ
5.47 3.47 x 10^4 Joules
5.49 -45.7 kJ/ mol NaOH
5.50 25 kJ/mol NH 4 NO 3
5.58 a) 125 kJ b) See energy diagram.
c) No, we are tracking heat and if the products are at an elevated temperature, then the amount of heat required to get them to that temperature must be accounted for as well. (Do this by taking into consideration the specific heat of the material and the temperature difference. Specific heat is a characteristic of a material. It is defined as the amount of heat required to raise the temperature of 1 gram of material by 1 °C.)
E
Y
X
Z
90 kJ
35 kJ
5.60 -867.7 kJ
5.63 See text A-
5.68 a) ½ H 2 (g)+ ½ Br 2 (g) Æ HBr (g) ∆H (^) f°(HBr(g)) = -36.23 kJ/mol ; ∆Hrxn=-36.23 kJ
b) Ag (s) + ½ N 2 (g)+ 3/2 O 2 (g) Æ AgNO 3 (s) ∆H (^) f°( AgNO 3 (s)) = -124.4 kJ/mol ∆Hrxn = -124.4 kJ c) 2Hg (l) + Cl 2 (g) Æ Hg 2 Cl 2 (s) ∆H (^) f°(Hg 2 Cl 2 (s)) = -264.9 kJ/mol ∆Hrxn = -264.9 kJ
d) 2 C (s, graph)+ 3H 2 (g) + ½ O 2 (g)Æ C 2 H 5 OH (l) ∆Hf° (C 2 H 5 OH (l)) = -277.7 kJ/mol ∆Hrxn = -277.7 kJ 5.72 a) -976.94 kJ/mol (yes, the answer book made a mistake on this one)
8.61 a) 304 kJ/mol b) 82 kJ/mol