Ch. 5, 19, 10  thermodynamics & gas  test     [65 points]       AP  Chemistry

For problems involving calculations, show the relevant equation (or formula and conversion factor(s)), show your work in an organized manner, put the proper units in your calculations / answer, and have the proper number of significant figures in your answer. 

Academic Honesty:   The answers on this test are my own and I am using only the allowed set of notes as described in the syllabus.  I have not discussed the test questions with anyone before or during the test nor have I seen the test questions prior to the exam.  If you violate any of the preceding items or do not sign, your semester grade is a F.
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1.   Based on the following information,    [15 points]

• Bond enthalpy (kJ / mole)

C – C:  348                  O –H:  463      C = O:  799
C – O:  358                 O₂ :     495       C ≡ O:  1072

• C₂ H_{6 (g)}   +  O_{2 (g)}   ->  CO_{2 (g)}   +  H₂ O _(g)

a.  determine ΔH for the combustion of ethane using the table of ΔHf

b.  determine ΔH for the combustion of 10.0 g of ethane

c.  determine the bond enthalpy of the C – H bond.

2.   2.0 g (solid) KOH was dissolved in 65 mL water.  [20 points]

a.  write  the chemical equation that describes this process.

b.  calculate the ΔH of the preceding reaction.

c.  calculate the change in temperature of the water  (assume the specific heat of water = 4.18 J / (g °C) due to dissolving KOH.

d.  if the initial temperature was 21.0 °C, what is the temperature of the solution immediately after all of the KOH dissolved ?

3.  Using thermodynamics, calculate the boiling point of water.  [10 points; hint:  find the temperature, where ΔG < 0 for the reaction describing to boil water]

4.  A syringe with a volume of 35 mL has a pressure of 95 kPa at 22 °C.  The volume of the syringe was reduced to 25 mL and its temperature to – 5 °C.  What is the pressure in the syringe ?  [10 points]

Old topic:  boiling point

5.  The boiling point of HCl is less than the boiling point of Cl₂ .  Rationalize this observation.  [10 points; send you an email of this question with its answer]