Unit 10 Learning Log
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Concepts: Explain each thoroughly and describe helpful examples. Diagrams would be useful:
Enthalpy, entropy, Gibbs free energy, compare G to Go , using the 2 equations for ΔGo explain the effect on Keq for increasing and decreasing the temperature of an exothermic reaction
1- Using the data from Appendix C, calculate Ho ,So , Go at 298 K for the following reaction:
2CH3OH (g) + H2(g) C2H6(g) + 2H2O (g)
2- Consider the following reaction:
NO2(g) + N2O(g) 3Nog
(a)Use the data in Appendix C to predict how Go for the reaction will vary with increasing temperature (b) Calculate Go at 800 K , assume enthalpy and entropy are unchanged. Is the reaction spontaneous at 800 K ? (c) calculateGo at 1000 K. Is the reaction spontaneous at this temperature?
3- Explain qualitatively how G changes in each of the following reactions as the partial pressure of O2 is imcreased:
(a) 2CO(g) + O2 (g) 2CO2(g)
(b) 2H2O2 (l) 2H2O(l) + O2(g)
( c) 2KClO3(s) 2KCl(s) + 3O2(g)
4- Consider the decomposition of barium carbonate:
BaCO3(s) BaO(s) + CO2 (g)
Using the data in appendix C,calculate the equilibrium pressure at(a) 298 K and(b)1100K
5- For the reaction:
XSO4(s) X+2 (aq) + SO4-2
H = 5800 cal and X is unknown. Does the solubility of the solid increase or decrease as temperature increases? Explain. At 25C the solubility product of XSO4 is 1.1x10-10 ? What is the value at 90C, given that enthalpy for the reaction is constant.
6- Use the following problem to explain how you can solve for G0 and the equilibrium constant( k ) when you are given Hof and So for the reactants and products. How would a change in temperature affect your calculations?
Compound Hof (kj/mol)So (j/mol)
H2O(l) -286 69.8
CO2(g) -393 214
O2 (g) 0.0 205
C3H8 (g) ? 269.6
When 1.0000 gram of propane gas C3H8) is burned at 25oC and 1.00 atm, H2O (l) and CO2 (g) are formed with the release of 50.3 kj (hint: that is -50.3 kj)
a) Write a balanced equation for the combustion of propane.
b) Calculate the molar enthalpy of combustion, (Ho comb,) of propane gas.
c) Calculate the standard molar enthalpy of formation ( Hfo) of propane gas.
d) Calculate the entropy change, (So comb) for the combustion reaction and account for the
sign of So comb.
e) Calculate the free energy (Go) for the combustion of propane.
f) Calculate the equilibrium constant for the reaction
g) What happens to the equilibrium constant if the temperature is increased?
7- Answer the following questions that relate to the chemistry of nitrogen.
(a)Two nitrogen atoms combine to form a nitrogen molecule, as represented by the following equation.
2 N(g ) ↔ N2(g)
Using the table of average bond energies below, determine the enthalpy change, ∆H, for the reaction.
Bond / Average Bond Energy (kJ mol–1)N–N / 160
N=N / 420
NN / 950
(b)The reaction between nitrogen and hydrogen to form ammonia is represented below.
N2(g) + 3 H2(g) ↔ 2 NH3(g)∆H˚ = –92.2 kJ
Predict the sign of the standard entropy change, ∆S˚, for the reaction. Justify your answer.
(c)The value of ∆G˚ for the reaction represented in part (b) is negative at low temperatures but positive at high temperatures. Explain.
(d)When N2(g) and H2(g) are placed in a sealed container at a low temperature, no measurable amount of NH3(g) is produced. Explain.
8-Using the data in Appendix C, calculate the standard enthalpy, standard Gibbs free energy and the equilibrium constant(at 298 K) for the production of ozone from oxygen:
3O2 (g) ↔ 2O3 (g)
At 30 km above the surface of the Earth, the temperature is about 230K and the partial pressure of oxygen is about 1 x 10-3 atm. Calculate the partial pressure of ozone in equilibrium with oxygen at 30 km above the Earth’s surface. Is the equilibrium maintained under these conditions? Explain your response
9- WO3(s) + 3 H2(g) ↔ W(s) + 3 H2O(g)
Tungsten is obtained commercially by the reduction of WO3 with hydrogen according to the equation above. The following data related to this reaction are available:
WO3(s)H2O(g)
∆Hfo (kilocalories/mole)-200.84-57.8
∆Gfo (kilocalories/mole)-182.47-54.6
(a)What is the value of the equilibrium constant for the system represented above?
(b)Calculate ∆So at 250C for the reaction indicated by the equation above.
(c)Find the temperature at which the reaction mixture is in equilibrium at 1 atmosphere.
10- 2 NO(g) + O2(g) 2 NO2(g)
H°= -114.1 kJ, S°= -146.5 J K-1
The reaction represented above is one that contributes significantly to the formation of photochemical smog.
(a)Calculate the quantity of heat released when 73.1 g of NO(g) is converted to NO2(g).
(b)For the reaction at 25C, the value of the standard free-energy change, G, is -70.4 kJ.
(i)Calculate the value of the equilibrium constant, Keq, for the reaction at 25C.
(ii)Indicate whether the value of G would become more negative, less negative, or remain unchanged as the temperature is increased. Justify your answer.
(c)Use the data in the table below to calculate the value of the standard molar entropy, S, for O2(g) at 25C.
Standard Molar Entropy, S (J K-1 mol-1)NO(g) / 210.8
NO2(g) / 240.1
(d)Use the data in the table below to calculate the bond energy, in kJ mol-1, of the nitrogen-oxygen bond in NO2 . Assume that the bonds in the NO2 molecule are equivalent (i.e., they have the same energy).
Bond Energy (kJ mol-1)Nitrogen-oxygen bond in NO / 607
Oxygen-oxygen bond in O2 / 495
Nitrogen-oxygen bond in NO2 / ?