13.4 NOTES Pressure

A.4 Pressure Pressure- force over area that force is applied on   Less area with same force = greater pressure Measured in pascals (Pa), which is the SI unit for pressure These are very small, so kilopascals, or kPa, are used, which are 1000 times greater in size than Pa

International System of Units International standard for the metric system  Base units Express fundamental physical quantities of the modernized metric system Length, mass, time, temperature, quantitiy (mole), electric current, luminous intensity  Derived units Made of 2+ base units Area, volume, pressure

A.6 Atmospheric Pressure Pressure the atmosphere exerts on the Earth’s surface   Standard atmospheric pressure is equal to 1 atmosphere, which is abbreviated atm. 1 atm = 101.3 kPa = 760 mmHg

Barometer- device for measuring atmospheric pressure  

Datlon’s Law of partial pressure – total pressure of a mixture of gasses is equal to the sum of the individual pressures of all gasses  present Ptotal = P1 + P2 + P3 + ……

Ptot = PO2 + PH2O 49.2 kPa = PO2 + 23.4 kPa PO2 = 25.8 kPa Example: Oxygen gases is collected over water. If the total pressure of the system is equal to 49.2 kPa, and the pressure of the water vapor is 23.4 kPa, what is the pressure of the oxygen gas? Ptot = PO2 + PH2O 49.2 kPa = PO2 + 23.4 kPa PO2 = 25.8 kPa

A.7 Atoms and Molecules in Motion Review solids, liquids, and gases are held together by intermolecular forces   These forces are strongest in solids and weakest in gases

Kinetic molecular theory   Explains gas behavior Gases consist of tiny particles in constant random motion Molecules bang against each other and the walls of the container in elastic collisions (energy is conserved) As temperature increases, KE and velocity increase (KE = 1/2mv2) At the same temp, all gases have the same KE.