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# Thermochemical Equations

## Describes the incorporation of enthalpy into a reaction equation

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Hydrogen Fuel Cells

### Hydrogen Fuel Cells

Credit: Steve Jurvetson
Source: http://en.wikipedia.org/wiki/File:Tesla_Model_S_Indoors_trimmed.jpg

In the modern world we get most of our energy from burning fossil fuels (think gasoline and crude oil). This energy releasing process produces carbon dioxide (CO2) as a waste product. It is commonly accepted that the resulting “carbon footprint” is leading to a change in the global climate. However, with fuel cell driven cars like those above now you can fight “carbon” with “hydrogen”!

#### Amazing But True!

• Energy, which is the ability to do work, is all around us. The challenge is to capture it, store it and use it in ways that are convenient for us. Chemical bonds in molecules are one way to store energy (a form of potential energy).
• In fact, hydrogen molecules (H2) store a significant amount of energy in the H-H single bond. When two molecules of hydrogen combine with one molecule of oxygen (O2) the product is two molecules of water. The total energy in all of the bonds of the two water molecules is less than all of the total energy in the bonds of the starting H2 and O2. Where did the rest of the energy go? If you used a hydrogen fuel cell to facilitate this transformation then much of the energy was converted to useful electrical energy!
• Credit: Steve Jurvetson
Source: http://www.flickr.com/photos/jurvetson/6278224744/

Fuel cell used on the Apollo space mission. The byproducts of water and heat were both useful resources in space. Water was for drinking and the heat helped to control the temperature in the shuttle [Figure2]

• To be clear, the use of hydrogen fuel cell technology still requires the production of hydrogen gas, which requires energy. However, the hope is that hydrogen gas can be produced without the use of fossil fuels. Can you think of some ways to generate hydrogen gas without the use of fossil fuels?
• To see how the US Navy is thinking about hydrogen fuel cell, watch the following video:

#### Can You Apply It?

1. Write out the chemical equation for the reaction that is operative in a hydrogen fuel cell.
2. Gasoline can provide roughly  12 kWhkg\begin{align*}12 \ \frac{kW\cdot h}{kg}\end{align*} of energy from combustion. Recall that a Watt is a Joule/second (W=Js)\begin{align*}\left(W=\frac{J}{s}\right)\end{align*}. How many Joules of energy can be derived from the combustion of 1 kg of gasoline?
3. Based on the reading in the links below, you should know that 1 mole of hydrogen gas can furnish approximately 237 kJ of electrical energy. How much electrical energy could be harvested from 1 kg of hydrogen gas?
4. Do you think hydrogen fuel cells will solve all of our energy problems? Are their any shortcomings of hydrogen?

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