Ch. 5, 19, 10  thermodynamics & gas            test  70 points                                 AP chem

For problems involving calculations, show your work in an organized manner, include any relevant equation (or formula and conversion factor(s)), 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.  An eudiometer tube is used to measure the volume of a gas in a reaction.  An unknown amount of Mg reacting with excess HCl produced 35 mL of gas in the eudiometer tube; the atmospheric pressure is 750 mm Hg; temperature = 50 °C; the fluid in the eudiometer tube was 10.0 cm higher than the surrounding fluid.  What was the mass of Mg in the reaction ?  hint;  10.3 m water = 1.0 atm.  [10 points]

2.  If a hypothetical gas effuses 4 times slower than methane gas, what is its molar mass ?  [5 points]

3.  2.0 g solid potassium hydroxide dissolves in 150. mL water at 19 °C.  What is the temperature of the water after all of the potassium hydroxide dissolved in water ?   [15 points]

4.  How much heat would be produced in the complete combustion of 1.0 g of an aldehyde containing a methyl group ?  [15 points]

5.  In regards to the change in enthalpy to dissolve solid sodium hydroxide in water,   [15 points]

a.  what is the ΔS of this process ?

b.  what are the two factors that could qualitatively account for the sign of ΔS of this process ?

c.  which of the preceding two factors has a greater effect on the sign of ΔS for this process ?  justify your choice.

6.  old topic:  valence bond theory  [10 points]

Using valence bond theory, describe the bonds in the nitrogen molecule.  Clearly indentify:  the atomic orbitial / hybrid orbital involved in the bonds & type of bonds (i.e. pi versus sigma).  Hint:  email send during the winter break