Humboldt State University ® Department of Chemistry

Richard A. Paselk

Chem 107	Fundamentals of Chemistry	Fall 2008
Lecture Notes: 4 November	© R. Paselk 2005
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Gases and Gas Laws, cont.

What is Pressure? Due to collisions of particle with walls of container etc.

Units of Pressure:

• mmHg
• atm
• others include psi (pounds/square inch), pascals, Torr, etc.

Gases are characterized by four properties

• Amount of substance, n  (in moles)
• Volume, V (in Liters)
• Pressure, P (in atm, though often measured in mmHg)
• Temperature (in K)

Boyle's Law

Boyle's describes the relationship between pressure and volume when the temperature and amount of substance are held constant.

Or, "At constant temperature the volume of any quantity of gas is inversely proportional to its pressure." V = k (1/P), or PV = k, & P₁V₁ = P₂V₂.

Plotting pressure volume data (keeping n and T constant) gives a graph for a hyperbola (xy = c), as seen below:

Charles' Law

The relationship between volume and temperature was determined much later because accurate thermometers had to be developed first. But once thermometers were available a number of workers determined that volume is directly proportional to temperature. Plotting data for the relation of volume of a gas to temperature between 0° C and 100 ° C gives a plot similar to that below:

Extrapolating this data to V = 0 we can find an absolute minimum value of temperature on the assumption that negative volumes can't exist:

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Last modified 4 November 2008