Gasses Kinetic molecular theory Pressure

Introduction Earth’s atmosphere is a gaseous solution composed of mostly nitrogen and oxygen The atmosphere is important for life on earth – Provides a medium for many chemical reactions with waste products – Shields the Earth from harmful radiation – Retains heat on earth’s surface The behavior of gas particles contributes to their important properties

States of Matter Atoms/Molecules in all states of matter have attractive forces – Strongest in solids, weakest in gasses – Affected by changes in temperature Kinetic energy (KE) = energy of motion Temperature = a measurement of kinetic energy SolidsLiquidsGases Definite shape X Definite volume XX Takes the shape of its container XX Cannot be compressed XX

Kinetic Molecular Theory Gasses consist of tiny particles The particles are so small (compared between the distances between them) that the individual particles have nearly no volume The particles are in constant random motion, colliding with the walls of the container. These collisions cause the pressure exerted by the gas. The particles are assumed not to attract or repel each other. The average kinetic energy of the gas particles is proportional to the Kelvin temperature of the gas.

Pressure Gas fills any container uniformly – It is evenly spread out Gasses exert pressure on their surroundings – Example: when you blow up a balloon, the gasses inside push against the sides and keep it firm. A Barometer measures atmospheric pressure – Invented by Evengelista Torricelli in 1643 Atmospheric pressure results from the air being pulled by gravity – Varies with altitude – Changes with weather conditions

Units of Pressure The units for pressure are based on the height of the mercury column (in millimeters) that the gas pressure can support – mm Hg (millimeters of mercury) is also called torr Standard atmospheres (abbreviated atm) are also used. 1 standard atm = atm = mm Hg = torr The SI unit for pressure is the pascal (Pa) 1 atm = 101,325 Pa Engineers use pounds per square inch (psi) atm = psi

Pressure Unit Conversions Convert the following to atmospheres: kPa (1 kPa = 1000 Pa) torr mm Hg Convert the following into units of mm Hg: psi kPa atm Convert the following into kilopascals (kPa) 7.105,390 Pa mm Hg atm torr