1)Which of the following processes involves an increase in entropy? a. the combi
ID: 840817 • Letter: 1
Question
1)Which of the following processes involves an increase in entropy?
a. the combination of H2(g) and N2(g) gas to form NH3
B. the combination of Na and Cl to form NaCl in water
C. the evaporation of liquid water to steam
E. the condensation of ethanol
2. For the following reaction at 25 degrees C-
2C(s)+ O2(g) --> 2CO2 (g)
calculate delta S univ given delta S sys = 179.1J/K and delta H sys = -221.1kJ
3) Use the following thermodynamic data
Species delta H (kJ/mol) S(J/K*mol)
H2O2 (l) -187.78 109.6
H2O(l) -285.83 69.91
O2 (g) 0 205.14
to calulate delta S univ for the decomposition of hydrogen peroxide at 25.0 C
2H2O2 (l) --> 2H2O(l) + O2(g)
4) Diluting concentrated sulfuric acid with water can we dangerous, The temperature of the solution can increase rapidly, What are the signs of deltaH deltaS and deltaG for this process?
5) A chemical reaction at equillibrium, if deltaG = 0 then
a. K>1
b. K=0
c K<1
d K<0
e. K=1
Explanation / Answer
1
C. the evaporation of liquid water to steam
2
You have to use one of the TdS equations. For this particular process
Delta S = R ln( Vf / Vo )
where R is the gas constant, T is the temperature, Vf is the final volume and Vo is the initial volume. That is the change of entropy in the system.
From the 1st law of thermodynamics for closed systems we have
Q = W + U
in this case, the process is isothermal, thus U=0 and then
Q = W
This heat must be provided by the surroundings, thus the change in entropy of the surroundings is
Delta Ssurr = Q/T = - W/T = - Delta Ssyst.
And the generated entropy (change of entropy in the universe) is just
S gen = Delta Ssurr + Delta Ssys = 0
there is no entropy change in the universe for this process.
3
2 H2O2(l) ? 2 H2O(l) + O2(g)
?Srxn = ?Sprod - ?Sreact
?Srxn = 2 x ?Sh2o + ?So2 - 2 x ?Sh2o2
?Srxn = (2 x 69.91) + 205.14 - (2 x 109.6)
4
The reaction gives of heat (exothermic: ?H < 0).
Disorder increases with mixing (?S > 0).
?G = ?H - T?S < 0
5
c K<1
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