Workshop 8: Gibb\'s Free Energy A fuel cell is a device that converts the energy

Question

Workshop 8: 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 AG of the process. So the maximum electrical work done can be obtained from AG run and if both AHO and AS are known it can be calculated using AG AHO TASO 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 I. (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 (CsH180 in oxygen to produce carbon dioxide gas and liquid water: (a) 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 justif them! (a) (b)

Explanation / Answer

PART 1

Q1.

a)

balance equation for:

reaction of 1 mol of H2(g) i Oxygne to produce water

H2(g) + 1/2O2(g) --> H2O(l)

b)

1 liq mol of octane to CO2 + H2O

C8H18(l) + O2(g) = CO2(g) + H2O(l)

balance

C8H18(l) + O2(g) = 8CO2(g) + H2O(l)

C8H18(l) + O2(g) = 8CO2(g) + 9H2O(l)

C8H18(l) + 25/2O2(g) = 8CO2(g) + 9H2O(l)

Q2.

a) better for the environment is clearly H2(g) since it will only produce water, no CO2(g)

b)

Easier to use --> Octane, since it is a liquid which is flammable (pretty easy)

safer --> most likely octane, since H2(g) is pressurized and can explode with mechanical stresss

Easier to transport/store --> Octane, since it is a liquid, H2 must be compressed

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