Pressure and Intro to Gases

Which of the following hold true for most gases? A. Gas molecules are far apart B. Gas molecules move randomly C. Gas molecules themselves have essentially no volume D. All of the above E. None of the above

Kinetic Molecular Theory Holds true for ideal gases Most gases behave ideally near standard temperature and pressure 5 postulates/tenets about gas molecules: Constant, random motion No attractive/repulsive forces between molecules (they’re too far apart to have intermolecular forces) Negligible volumes compared to the container occupied Kinetic energy increases as temperatures increase Elastic collisions

There are 4 variables that can be used to describe a sample of gas Pressure (P) Temperature (T) Volume (V) Number of moles (n)

Pressure The force acting on a specific area Pressure(P) = force area Which of the following would be the greatest pressure? A)Standing on one foot in cowboy boots B)Standing on two feet in cowboy boots C)Standing on one foot in high heels D)Standing on two feet in high heels

Units of Pressure Look at your conversion chart…. mm Hg is millimeters of mercury….strange…a height of a substance is a pressure….historical

What was the force keeping the mercury in the glass tube? Atmospheric pressure was first measured in 1643 by Italian Torricelli while ‘playing’ with mercury

Giant Water Barometer, Netherlands, 1990

A water barometer is 13.6 times taller than a mercury barometer (density of mercury = 13.6 g/mL) because A) water is less dense B) water is heavier C) Air is more dense than water D) I don’t know

Units of Pressure Look at your conversion chart…. Convert 10 psi to mmHg Convert 2.01 atmospheres into pascals Convert today’s pressure into atmospheres

What’s Your Foot Pressure? Trace the outline of your shoe on the graph paper in your lab notebook (a partner may need to help ) Calculate your pressure in psi. [Hint: what information would you need to calculate psi?] Convert it to atm. Convert your pounds-per-square-inch into kiloPascals (kPa).