General Chemistry II Workshop 7: Gibb\'s Free Energy A fuel cell is a device tha

Question

General Chemistry II Workshop 7: Gibb's Free Energy A fuel cell is a device that converts the energy produced in a chemical reaction into electricity. The reaction that powers the PEM (Proton Exchange Membrane) fuel cell is the same as when hydrogen gas simply burns in the presence of oxygen. The amount of work other than the expansion work that a reaction can produce is given by the Ge ofthe process. So the maximum electrical work done can be obtained from Gena and if both rand ase are known it can be calculated using In this workshop we will calculate the maximum possible energy in form of electrical work that can be extracted from a fuel cell and will compare this amount with the amount of electrical work that can be obtained from the oxidation of a hydrocarbon fuel octane (liquid at room temperature and pressure). Part L. (2 pts) Write down and balance chemical equations for (a)the reaction for burning 1 mole of hydrogen gas in oxygen to produce liquid water and (b) the reaction for burning 1 mole of liquid octane (CaHi8) in oxygen to produce carbon dioxide gas and liquid water Now look at the two reactions and discuss with your group the following questions: (a) Which of these two methods of obtaining energy is better for the environment? (b) If you want to use these two fuels, hydrogen gas or liquid octane, directly which one of them is easier and safer to store and transport? Now write down your answers below and don't forget to justify them! Name H2(g) 02(g) H20(g) Hou) CO2(g kJ/mo 0.0 0.0 241.8 -285.8 393.5 252.1 0.0 0.0 228.6 237.1 394.4 130.7 205.2 188.8 0.0 213.8 361.1

Explanation / Answer

Part I :
(a) H2 (g) + 1/2 O2 (g) ------> H2O (l)
(b) C8H18 (l) + 12.5 O2 (g) --------> 8 CO2 (g) + 9 H2O (g)

a) For the benefit of environment the production of hydrogen gas is better than octane because
it produces water which can be used and does not give away gases like CO2
(b) liquid fuels are easy to transport rather than gaseous ones, hence liquid octane is easy to transport.

1) (a) Hrxn = [ 1mol*(-241.8)kJ/mol] - [1mol*(0kJ/mol) + 1/2*(0kJ/mol)]
   Hrxn = -241.8 kJ
(b)Hrxn= nHf,products - nHf,reactants
Hrxn = [8*(-393.5)+ 9(-285.8)] - [1*(-252.1)+ 12.5*(0)] = -5648.1 kJ

2) a) calculating Srxn first ,
  Srxn = [1*188.8]-[1*130.7 + 1/2*205.2] = -44.5 J/K= -0.0445 kJ/K
Grxn =  Hrxn - T Srxn = -241.8 kJ - (298K)*(-0.0445)kJ/K = -228.539 kJ
(b) Srxn = [8*213.8 + 9*70] - [1*361.1 + 12.5*205.2] = -585.7 J/K = -0.5857 kJ/K
  Grxn = -5648.1 - 298( -0.5857) = -5473.56 kJ
Liquid octane is more effcient than hydrogen gas.

Related Questions

Navigate

• Browse (All)
• Browse G
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.