A-As the temperature of a reaction with D S ° > 0 is increased, the equilibrium
ID: 1015146 • Letter: A
Question
A-As the temperature of a reaction with DS° > 0 is increased, the equilibrium constant __________
a.
always increases.
d.
increases only when DH° > 0.
b.
always decreases.
e.
increases only when DH° < 0.
c.
always stays the same.
B-A sealed tube containing an equilibrium mixture of NO2(g) (brown) and N2O4(g) (colorless) is subjected to a variety of temperatures. For the equilibrium reaction shown, the values of the DH° and DS° are also shown. What is observed in the tube with increasing temperature?
2 NO2(g) DN2O4(g) DH° = –58.02 kJ/mol, DS° = –176.5 J/mol × K
a.
At higher temperatures, the gas in the tube has a darker brown color.
b.
At higher temperatures, the gas in the tube has a lighter brown color.
c.
At higher temperatures, the gas in the tube is colorless.
d.
The color does not change with temperature.
e.
At higher temperatures, the gas turns green.
C-When plotting ln K vs. 1/T, a linear relationship is obtained __________
a.
with a slope of –DH °/R and an intercept of +DS°/R.
b.
with a slope of –DH °/R and an intercept of –DS°/R.
c.
with a slope of +DH °/R and an intercept of +DS°/R.
d.
with a slope of +DH °/R and an intercept of –DS°/R.
e.
never, as logarithmic relationships are intrinsically nonlinear.
D-A reaction X + 2 Y D 3 Z is started with 1.0 M Z and no X or Y. To calculate the equilibrium concentrations of all species using a RICE table, which of the following would you enter in the Z column for the C row?
a.
1.0 M
d.
1.0 M + 3x
b.
1.0 M – x
e.
–3x
c.
1.0 M – 3x
E-When can an x be ignored in solving an equilibrium expression derived from a RICE table?
a.
whenever it simplifies the calculation
b.
whenever it is very much smaller than the term it is added to or subtracted from
c.
whenever the equilibrium concentration for that species is relatively very small
d.
whenever it is raised to any power higher than 1
e.
never
F-A student determined the equilibrium concentration in the following equation by neglecting the x term in the denominator. Was the student justified in this approximation? Why or why not?
K = 4.0 ´ 10–2 =
a.
Yes, the concentration > K, so the x can be ignored.
b.
Yes, the value of x determined in this way is less than 0.05, so it can be ignored.
c.
No, the value of x determined in this way significantly reduces the denominator.
d.
No, the value of x can never be ignored in solving an algebra problem.
e.
No, the value of K is much less than 1 so x cannot be ignored.
G-HIO3 behaves as acid in water: HIO3(aq) D IO3-(aq) + H+(aq), with Kc = 0.17 at 25°C. What is the H+ concentration in a solution that is initially 0.50 M HIO3?
a.
0.22 M
d.
0.29 M
b.
0.17 M
e.
0.34 M
c.
0.28 M
H-The decomposition of NOCl to form NO and Cl2, 2 NOCl(g) D 2 NO(g) + Cl2(g), has a Kp value of 1.6 ´ 10-5 at some temperature. If 0.500 atm of NOCl is placed in a closed vessel and allowed to come to equilibrium, what is its approximate equilibrium partial pressure?
a.
0.013 atm
d.
0.49 atm
b.
0.025 atm
e.
0.50 atm
c.
0.48 atm
a.
always increases.
d.
increases only when DH° > 0.
b.
always decreases.
e.
increases only when DH° < 0.
c.
always stays the same.
Explanation / Answer
A)
recall that dG = dH - T*dS > 0 in order to be spontaneous, therefore, if dG is negative, then K increases, then... dS must be positive and must increase in order to lower dG, which will increase K... Then the answer is always increases
B)
This is Exothermic, meaning that it releases heat as it goes in the forward direction. dG = dH - T*dS; since dS is negative, then TdS must be low and dH must be always negative... It will only be possible at Low temperatures so dG < 0. Then, at high T, the expected value of NO2 is likely to occur, the color will be brown. Choose A
C)
ln(K) vs 1/T is mainly the Ahrrenius equation ploted for linearity. Then, the slope is given as -dH/R and y-intercept as dS/R always from the list, choose A
D)
Data for Z: (R)eactant = Z; (I)nitially Z 1; the (C)hange of Z = 3x; in (E)quilibrium Z = 1+3x
E)
We can ignore x whenver the equilibrium concentration is much larger than the dissciation i.e. 1000 >>> x , assuming x = 0.01; then choose B
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