2003. 6.23
1.Show that as the temperature increases the most probable speed increases but
the spread of the speeds increases more markedly, and also that the fraction
of molecules with the highest speeds increases much faster with temperatures
than the average speeds. All the above facts reason why temperature has such
a large effect on chemical reaction rates.
2.Reading:Ionic reaction and salt effects
The denaturation process CO-hemoglobin by reaction with monovalent H+ is
denoted by
M+N ←→ MN(++) ─K(++)→ denatured product (1)
The reaction rate V is considered to be proportional to the concentration
(C(++)) of activated complex MN(++) at a given temperature,
V = k(++)*C(++) = k*CM*CN (2)
where k is the observed reaction rate constant.
It is assumed the reactants are in rapid equilibrium with the reansition
state MN(++) with the equilibrium constant between the transition state and
reactants
K(++) = [MN(++)]/[M][N] = C(++)*γ(++)/CMγMCNγN (3)
Thus
V = k(++)*K(++)CMγMCNγN/γ(++) (4)
Apparently, We have
k = k(++)*K(++)γMγN/γ(++) (5)
We mat then take advantage of Debye-Huckel limiting law
logγi = -0.51(Zi^2)√I (at 25度C) where I = 0.5ΣCi(Zi^2) (6)
To calculate the effect of ionic strength on reactant rate for
M+N → MN(++)
logk = log(k(++)K(++)) + logγM + logγN - logγ(++)
= log(k(++)K(++)) - 0.51[(ZM^2)+(ZN^2)-(Z(++)^2)]√I
= log(k(++)K(++)) - 0.51[(ZM^2)+(ZN^2)-((ZM+ZN)^2)]√I
= log(k(++)K(++)) + 2*0.51*ZMZN√I (7)
A plot of logk vs √I for dilute ionic solution may give direct information
about charges of the reactants.
(1)Based on Eq(7), discuss the salt effect of ionic reaction i.e. the effect
of ionic strength in solution on reaction rate.
(2)The acid-denaturation of CO-hemoglobin has been studied at pH 3.42 in a
formic acid-sodium formate buffer (Na+ + HCOO-) concentration. The
half-life for first-order denaturation are as follows
HCOONa(m) 0.007 0.010 0.015 0.020
t1/2(min) 20.2 13.6 8.1 5.9
For a first-order reaction k = 1n2/(t1/2) = 0.693/(t1/2)
Determine whether these results follows the Debye-Huckel limiting law in
the dependence of the rate constant on ionic strength and, if so, what is
the apparent charge on the CO-hemoglobin?
3.The solubility of sodium propionate NaOPr in water at 25度C is 9.8mol/dm^3
and logγ± = -0.2454 + 0.103C near this concentration C in mol/dm^3.
Calculate standard state Gibbs free energy change for
NaOPr(C) → NaOPr(aq.solution)
What would be the approzimate molality of NaOPr in its standard state in
solution?
4.From the data given in following table construct a complete
temperature-composition diagram for the system ethanol-ethyl acetate for
1.013 bar. A solution containing 0.8mole fraction of ethanol, EtOH, is
distilled completely at 1.013 bar.
(a)What's the composition of first vapor to come off, and
(b)What is that of the last drop of liquid to evaporate?
(c)What would be the values of these quantities if the distillation were
carried out in cylinder provide with a piston so that none of the vapor
could escape?
xEtOH yEtOH b.p.(度C) xEtOH yEtOH b.p.(度C)
0 0 77.15 0.563 0.507 72.0
0.025 0.070 76.7 0.710 0.600 72.8
0.100 0.164 75.0 0.833 0.735 74.2
0.240 0.295 72.6 0.942 0.880 76.4
0.360 0.398 71.8 0.982 0.965 77.7
0.462 0.462 71.6 1.000 1.000 78.3
5.The following osmotic pressures of polyvinyl acetate in dioxane were measure
by G.V.Browning and J.D.Ferry at 25度C
C/0.01 g/cm^3 0.292 0.579 0.810 1.140
Π/cm of solvent 0.73 1.76 2.73 4.68
Calculate the number average molar mass. The density of dioxane is
1.035g/cm^3
6.The effect of temperature on Kp is given by equation
Ky = Π(i=1~Ns) (yi)^vi = ((P/P0)^(-v))*K
and the effect of temperature on Kc is guven by
ΔU0 = R(T^2)*(δlnKc/δT)V
Is it possible for a gas reaction to have Kp increase with increasing
temperature, but Kc decrease with increasing T? If so, what has to be true?
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