Notes from Friday, Feb. 19

Homework for this weekend: Read ahead in the chapter. Print out the ideal Gas Law Constant Lab and do the pre-lab for Monday.

• Boyle's Law, Charles' Law, and Gay-Lussac's Law can be combined into a single equation that can be used for situations in which temperature, pressure, and volume all vary at the same time.
• This is the combined gas law, PV/T=k, or P1V1/T1=P2V2/T2.
• Each gas law can be derived from the combined gas law when the proper variable is kept constant.
• Sample Problem F can be found in your book.
• In the early 1800s, French chemist Joseph Gay-Lussac observed that 2L hydrogen can react with 1 L oxygen to form 2L water vapor.
• This reaction shows a simple 2:1:2 ratio in the volumes of reactants and products. This same ratio applies to any volume proportions.
• Gay-Lussas's law of combining volumes of gases (that's a mouthful) states that at constant temperature and pressure, the volumes of gaseous reactants and products can be expressed as ratios of small whole numbers.
• 1811: Avogadro explained Gay-Lussac's law of combining volumes of gases without violating Dalton's idea of indivisible atoms.
• Avogadro reasoned that, instead of always being in monoatomic form, when they combine to form products, gas molecules can contain more than one atom.
• Avogadro's law: equal volumes of different gases contain the same number of molecules, at given pressure and temperature. Also, gas volume is directly proportional to the amount of gas at a given temperature or pressure. V=kn.
• Dalton had guessed that the formula for water was HO, but Avogadro's reasoning established that water must contain twice as many hydrogen atoms as oxygen atoms because of the volume ratios in which the gases combine.
• Ergo, Avogadro's idea of diatomic gases was consistent with all other knowledge and laws.