1. Write a balanced chemical reaction for the combustion of hydrogen.

   

2. Is this reaction exothermic or endothermic?

   The reaction is exothermic.

Helium has a completely filled outermost electron shell, as do all the noble gases. Needing neither to lose nor gain electrons, it has little reason to react with other atoms to form chemical bonds. Therefore helium is inert and does not react with oxygen in the way hydrogen does.

Since equal volumes of different gases at the same temperature and pressure contain an equal number of molecules, a given volume of hydrogen will have the same number of molecules as an equal volume of helium. For example, one mole of H₂ and one mole of He will both occupy 22.4 L at STP. But one mole of He has a mass of 4 g, while one mole of H₂ has a mass of only 2 g. Since density is equal to mass divided by volume, H₂ must be less dense than He.

As the temperature of a gas increases, the volume will increase as well, if pressure is held constant. Therefore, a hot gas will occupy more volume than an equal amount of the same gas at a lower temperature. It then follows that the hotter gas, containing the same mass but occupying more volume than the cooler gas, must be less dense than the cooler gas. Therefore, hot air is less dense than cool air. For this reason, a balloon filled with hot air will float in the cooler air that makes up the atmosphere.

1. How did Gay-Lussac use balloons to study chemistry in the early 1800s?

   Gay-Lussac ascended in a balloon to an altitude of 23,000 feet above sea level. He took samples of the atmosphere at that height and determined the composition of the samples to see if they had the same composition as the air at sea level.

2. What did he learn from the investigations he carried out using a hot air balloon?

   His experiments showed the samples to have similar composition to sea-level air.

1. How did a paint made from powdered aluminum contribute to the disaster?

   Powdered aluminum is highly reactive and highly flammable.

2. How is powdered aluminum used on the Space Shuttle?

   Powdered aluminum is an ingredient in the rocket fuel used in the Space Shuttle's solid-fuel boosters.

3. Write the chemical equation for the reaction aluminum underwent in the disaster.

   

4. Is the reaction exothermic or endothermic?

   The reaction is exothermic.

5. Use the octet rule to explain why powdered aluminum can behave as it is thought to have done in the Hindenburg tragedy.

   Aluminum has three electrons in its outermost shell. The easiest way for it to obtain a stable electron configuration is to give up three electrons. So aluminum readily donates three electrons to oxygen when the opportunity arises. Thus, the powdered aluminum reacts with oxygen to form Al₂O₃.

6. Do you think an aluminum can would behave in the same manner as powdered aluminum? Why or why not?

   An aluminum can will not burn. The reason is that only aluminum atoms on the surface of a sample can react with oxygen. A sample of powdered aluminum has much more surface area than a large piece of aluminum of the same mass. Therefore, powdered aluminum is much more reactive than a large piece of the metal.

7. Describe the experiments carried out by Addison Bain.

   Bain tested the flammability of a surviving sample of the fabric that was the skin of the Hindenburg. A small flame was touched to the fabric, which completely burned up in seconds. In addition, Bain subjected a sample of the fabric to an electrical spark, which also caused the sample rapidly to combust.

8. Explain how his results and other evidence led to the conclusion that the skin of the Hindenburg was a major cause of the fire that destroyed the airship.

   Bain's first experiment showed that the skin of the Hindenburg was extremely flammable. The second experiment showed that the skin could have easily been ignited by an electrical spark. Since electrical sparking could have been likely given the electrical storm that was happening in northern New Jersey at the time the Hindenburg was landing, it is reasonable to conclude that an electrical spark ignited the skin of the airship, which burned violently and destroyed the airship in seconds.