At 25°C, the following heats of reaction are known: AH (kJ/mol 167.4 2CIF + 02 C
ID: 585419 • Letter: A
Question
At 25°C, the following heats of reaction are known: AH (kJ/mol 167.4 2CIF + 02 Cl20 + F20 2ClF3 + 202 Cl20+3F20 341.4 2F2 + 02 2F20 At the same temperature, calculate H for the reaction: ClF + F2 CIF3 -43.4 A. -217.5 kJ/mol B.-130.2 kJ/mol C. +217.5 kJ/mol D.-108.7 kJ/mol E. none of these QUESTION 4 Consider the reaction: When a 12.9-g sample of ethyl alcohol(molar mass 46.07 g/mol) is burned, how much energy is released as heat? A. 3.57 kJ OB, 3.84 × 102 kJ -, c. 1.77 × 104 KJ D. 0.384 kJ E. 0.280 kJ QUESTION 5 For a particular process q = 20 kJ and w = 15 kJ, which of the following statements is true? A. Heat flows from the system to the surroundings. B. The system does work on the surroundings. 0C. AE = 35 kJ D. All of the above are true. E. None of the above are true.Explanation / Answer
Q3
Apply Hes Law
if we need ClF + F2 = ClF3
from the data, invert RXN2 since we need ClF3, divide by 2
divide RXN1 by 2, since we need ClF with 1 coeff.
divide RXN 3 by 2, since we need F2 with 1 stoichiometric coeff
HTotal = -341.4/2 + 1/2*167.4 +1/2*-43.4
Htotal = -108.7 kJ/mol
Q4
mol of alcohol = mass/MW = 12.9/46.07 = 0.280
1 mol o = 1.37*10^3
0.280 mol --> X
x = 0.280*1.37*10^3 = 383.6 kJ = 3.84*10^2 kJ
Q5
Q = +20 kJ --> heat release
W = 15 kJ --> work on system
Q-W = dE
a)
is false, Heat flow TO the system
b)
this is true, system is being expanded
c)
False,
Q-W = dE
20-15 = dE = 5
d and e)
false
choose B
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