General Chemistry Sample Exam

Name ______________________________ SS# _________________________ Section _________

Instructions: Put your name, social security number, and section number on the top of this exam page. Answer the following six (6) parts in the notation and conventions of the lecture for a total of 100 points. Read the entire exam. Work alone and consult no one, living or dead, about this test (except Brucat) until after you leave the room. Notebooks, textbooks and any other study material is not allowed in the exam room. You may use only your own writing and calculating instruments (do not share). Show work where appropriate and write only on this exam page. Show proper units to receive credit.

R = 0.08206 L^.atm/mol^.K = 8.314 J/K^.mol

Part Ia
The van der Waals Equation describes the equation of state for a non-ideal gas.
(a) Write down what the van der Waals equation of state would look like if molecular stickiness was ignored for the gas.

(b) List the 3 major assumptions that imply the validity of the ideal gas equation of state

Part Ib
(a) Calculate the total kinetic energy of a mole of He gas at STP

(b) If a bicycle tire inflated with Air (mean mol wt=29 g/mol) deflates in a period of one (1.00) hour, how long will it take the same tire to deflate under the same conditions if it were filled with He?

Part II A gas sample is sealed in a vessel of fixed volume. The pressure of the gas in atmospheres is
determined accurately at several temperatures. The temperatures are measured with a new thermometer
which reads out in a new unit of temperature called the "degree Gator" or ^oG. Using the following table of
data only, predict the value of the absolute zero of temperature on the Gator temperature scale.

Temperature	Gas pressure
25 ^oG	1.35 atm
50 ^oG	1.55 atm
100 ^oG	1.95 atm

Part IIIa Consider the reaction A -> Products. Initially the concentration of A is 0.125 M. After 12 minutes the concentration of A is 0.110 M.
(a) What is the concentration of A after one hour if the reaction is first order in A?

(b) Under the same conditions as above, what would be the concentration of A after one hour if the reaction is second order in A?

Part IIIb The half life of a first-order reaction is found to drop from exactly one hour to 12.0 minutes upon a change in temperature from 10.0 ^oC to 50.0 ^oC. What is the half life of this reaction at 0.00 ^oC?

Part IVa Consider the following reaction:

2A + 3B + C -> D

Initial rate as a function of initial concentration data for this reaction is compiled in the following table:

[A]₀, M [B]₀, M [C]₀, M Initial rate, M/s

2.76 0.62 1.12 1.66 x 10³

1.52 1.52 2.24 2.20 x 10⁴

2.76 0.97 1.12 4.07 x 10³

1.52 0.25 1.12 1.49 x 10²

Show your Work:
The order of the reaction in A is ___________________
The order of the reaction in B is ___________________
The order of the reaction in C is ___________________
The rate constant for the reaction is ________________

Part IVb The time dependence of the chemical reaction A -> Products is studied by monitoring the depletion of the reactant at various times.
The following data is obtained:

time, minutes	[A], M
0.00	1.000
12.0	0.698
20.0	0.549
35.0	0.350
50.0	0.223

The half life of the above reaction is ____________________

Part V
A mixture of 0.71 mol of N₂ and 1.20 mol of H₂ are placed in a 3.0 liter vessel at 900K. When the reaction

N_{2 (g)} + 3H_{2 (g)} <-> 2NH_{3 (g)}

reaches equilibrium, the concentration of hydrogen gas is found to be [H₂] = 0.100 M.

(a)    What is the number of moles of H₂ in the reaction vessel at equilibrium?
(b)    What is the number of moles of N₂ in the reaction vessel at equilibrium?
(c)    What is the number of moles of Ammonia in the reaction vessel at equilibrium?
(d)    What is the total pressure of the vessel at equilibrium?
(e)    Qualitatively, what is the effect on the reaction equilibrium upon doubling reactor vessel pressure at constant temperature by the addition of Helium gas. (Hint: the vessel volume remains unchanged).
(f)    Qualitatively, what is the effect on the reaction equilibrium of doubling the temperature at constant pressure. (Hint: the reaction is exothermic as written)

Part VIa
Consider the reaction

XeF₂ + F₂ <-> XeF₄ ; K_C = 3.17 at 300 K.

A mixture of 0.52 moles of XeF₂ and 1.12 moles of F₂ are introduced into a 2.5 liter vessel. What is the equilibrium concentration, in moles per liter of XeF₄ at 300 K?

Part VIb
Consider the reaction A <-> B where the following thermodynamic data is known:

DH_rxn ⁰ = -14.0 kJ/mol
DS_rxn ⁰ = -55.0 J/K^.mol At what temperature does this reaction have an equilibrium constant of 1.00?
(Hint: Consider the standard enthalpy and entropy changes for this reaction to be temperature independent)

On my Honor, I have neither given nor received unauthorized aid in the execution of this exam

[A]₀, M	[B]₀, M	[C]₀, M	Initial rate, M/s
2.76	0.62	1.12	1.66 x 10³
1.52	1.52	2.24	2.20 x 10⁴
2.76	0.97	1.12	4.07 x 10³
1.52	0.25	1.12	1.49 x 10²