V/n=C

Avogadro’s Principle



Avogadro’s principle affirms that the the volume and the number of moles are directly related. When the temperature and pressure are held constant, the number of moles will increase as the volume increases and vise versa. For example, as a balloon is blown up with air (the moles of gas increase), it is obvious that the volume increases also.

Amadeo Avogadro and Joseph Louis Gay-Lussac were two prominent scientists whose works made it possible to understand this principle. Gay-Lussac investigated how gases (that were elements) combined to form gases (that were compounds). In his experiments, he used mostly Nitrogen and Oxygen. His analysis of the Nitrogen/Oxygen results showed that the ratios were simple, whole-number ratios. However, these were just close approximations. Actual data consisted of decimal numbers, but since these ratios were so close to whole numbers, they were rounded off to become whole numbers within experimental uncertainty.
Avogadro, a contemporary of Gay-Lussac, detected the importance of the law of combining volumes. He suggested that these principles could be defined easily. Avogadro hypothesized that equal volumes of gases had equal number of particles (or moles), at the same temperature and pressure.

In solving problems dealing with Volume and the number of moles, a proportion similar to P1/T1=P2/T2 can be set up. If the values for three of the four variables are known then the fourth can be easily found through cross-multiplication.

 

 

 

Sample Questions

1. If a 10 liter container held 1.5 moles of a gas, what volume will be needed to hold 3.4 moles of that gas at the same temperature and pressure assuming that the container can expand and contrast.

2. If 3.1 moles a chlorine gas was placed inside an 5 liter container, how many moles of chlorine can be placed inside a 30.5 liter container assuming all other conditions stay the same.

 

 

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PV = C V/n = C P/n = C V/T = C

P/T = C Tn = C

PV=nRT

 

Answers to Sample Problems

Answers to Sample Test