Youngstown State University
Department of Chemistry
Chemistry 3737(42725)
October 2, 2009
First Exam - 100 pts.
Name _______________________
Chap. 1-5, E&R, PChem.
[15 pts/Que]
ANSWER ANY 6 QUESTIONS – CIRCLE THEM
Constants and Equations: PV = nRT
[P + a(n2/V2)][V – nb] = nRT
-1
-1
R = 0.08205 lit.atm.mol K R = 8.314 x 10-2 bar dm3mol-1 K-1; dm3 = lit]
R = 8.314 J.mol-1K-1
CV = (3/2)R (monat/ideal) 1 atm = 1.013 bar
dw = -PextdV (PV work) , dU = dq + dw , dU = CvdT, dH = CpdT
dH = dU + d(PV)
Svap = Hvap/Tb
H = U + PV
Smix= -nR{xAlnxA + xBlnxB + ….}
A = U – TS
G = H - TS
-1
 = CP /CV
CP = CV + R (mol )
(T2/T1) = (V2/V1)1-γ (adiab.rev.0
C

dS = (dqrev/T) ∆S =   p  dT ∆S = nRln(V2/V1) + nCp ln(T2/T1)
T


(∂P/∂T)V(∂T/∂V)P(∂V/∂P)T = -1
Show your steps for full credit.
*1. Use the ideal gas and van der Waals equations to calculate the pressure of 3.00 moles of H2
if they are confined to a volume of 1.00 L at 298 K. [a = 0.2452 bar dm6mol-2, b = 0.0265 dm3
mol-1. Is the gas in the attractive or repulsive region of the intermolecular potential? Explain.
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PChem Exam 1 – Cont’d
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*2. Remembering that ΔH = ΔU + ΔnRT for a gas phase reaction, estimate the average bond
energy (ΔU) for the Si-F bond from the following data.
Reaction
ΔH(kJ mol-1)
Si(s) → Si(g)
450.0
F2(g) → 2F(g)
158.0
SiF4(g) → Si(s) + 4F(g) 1614.9
3. Remembering that κ = (1/V)(∂V/∂P)T and the β = (1/V)(∂V/∂T)P (the isothermal
compressibility coefficient and the isobaric thermal expansion coefficient),
and the cyclic rule, to find an expression for (∂U/∂V)T in terms of β, κ. P and T from
the expression below. Show its value for an ideal gas is zero.
(∂U/∂V)T = T(∂P/∂T)V - P
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PChem Exam 1 – Cont’d
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4. For the following reaction, calculate ∆Horx and ∆Sorx using the data supplied.
2 NaHCO3(s) + H2SO4(aq) → Na2SO4(s) + 2 CO2(g) + 2 H2O(l)
∆Hfo : -950.8
(kJ/mol)
So
:
(J/molK)
101.7
-909.3
-331.6
-393.5
-285.8
20.1
35.9
213.9
69.9
5. Explain what is meant by the Carnot limitation for all internal combustion engines, which
operate in a cyclic process to transfer heat spontaneously flowing from a high to a low
temperature reservoir, at least partly into work. (The efficiency of a heat engine is defined as
the work done divided by the heat given to the engine by the high temperature reservoir. The
qcycle = qh + qc and the sum of the (qi/Ti) over the cycle is also zero, making these quotients
state functions (S).
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PChem Exam 1 – Cont’d
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*6. 1.75 moles of an ideal gas with CV,m = (3/2)R are transformed from an initial state of
T = 750 K and P = 1.75 bar to a final state at T = 350K and P = 5.25 bar. Calculate
ΔU, ΔH and ΔS for this process. Show your steps for full credit.
7. For a mole of monatomic, ideal gas undergoing a reversible adiabatic expansion from 12.2 L
at 25 oC to a volume of 24.4 L, find the final temperature and calculate q, w, ∆U, ∆H, ∆S and
∆G for the gas. What is ΔSsurr and ΔSuniv process?
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PChem Exam 1 – Cont’d
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8. By using the First and Second Laws in differential form, dU = dq + dw and dS = dqrev/T, and
considering only PV work, dw = -Pdv, one may quickly note from substitution
dU = TdS - PdV
Using the definitions of H = U + PV, A = U – TS and G = H – TS, one may quickly generate
total differentials for dH, dA and dG. [Note: d(uv) = vdu + udv] Do this, and knowing that G
= f(T,P), identify the vital (∂G/∂T)p and (∂G/∂P)T coefficients.
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PChem Exam 1 – Cont’d
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Continued questions as needed
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