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Cell Reactions & Gases

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Question #1 The gas reaction N2(g) + 3H2(g) <--> 2NH3 (g) has K- = 0.80 at 600 K and Kp = 0.15 at 650 K

a) Is delta H greater than or less than zero?
b) Is the reaction exothermic or endothermic?

Question #2

The reaction N2 (g) + 3H2 (g) <---> 2HN3 (g) is at equlibrium

a) The number of moles N2 present plus he number of moles of H2 present must equal the number of moles NH3 present.
b) The number of moles N2 present plus three times the number of H2 present must equal two times the number of moles of NH3 present.
c) The number of moles of NH3 present does not change.with time.
d) Both (a) and (c) are true
e) Both (b) and (c) are true.

Question # 3

A cell that consists of an Ni, NiSO4(aq) half-cell, an Al, AlCl3(aq) half-cell, and a salt bridge.
For Ni^2+(aq) + 2e^- → Ni at 25C, Eo = -0.28 V. For Al3^+(aq) + 3e^- → Al at 25C, Eo = -1.66 V.
(a) Write the spontaneous net ionic cell reaction.
(b) Find E^o for this cell at 25 degrees Celsius.

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Solution Preview

Q1.

ln(K2/K1) = -(dH/R)(1/T2 - 1/T1)

ln(0.15/0.80) = -(dH/ 8.314)(1/650 - 1/600)

Hence dH = -108.56 kJ, so less than zero.

Hence reaction is ...

Solution Summary

Three questions based on equilibrium and electrochemistry are solved.

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Spontaneity of Reactions and Cell Potential

Consider the reaction below at 25 C:

3SO4^2- (aq) + 12H^+ (aq) + 2Cr (s) --> 3SO2 (aq) + 2Cr^3+ (aq) + 6H2O

(a) Is the reaction spontaneous at standard conditions?
(b) Is the reaction spontaneous at a pH of 3.00 with all other ionic species at 0.100 M and gases at 1.00 atm?
(c) Is the reaction spontaneous at a pH of 8.00 with all other ionic species at 0.100 M and gases at 1.00 atm?
(d) At what pH is the reaction at equilibrium with all other ionic species at 0.100 M and gases at 1.00 atm?

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