1. Chemistry Modeling 2013

2. Pressure Macro-Scale Pressure is the amount of force exerted over a given area The force exerted is caused by particles collisions with the surface of a “container” is a PRESSURE EVENT Familiar unit is “pounds per square inch” or psi (tire pressure) This is how many pounds of force something pushes on every 1 square inch of surface contact it has with an object Changes and effects of Pressure are only observed in gases (not liquids or solids)

3. Atmospheric Pressure Atmospheric pressure is the amount of pressure exerted on an object by all the particles in the atmosphere directly above that object Remember that air is made of particles, which have mass. That massive amount of atmosphere is pushing down on you at all times What affects atmospheric pressure? Elevation Temperature Amount of particles in the gas (water, particulate)

4. Measuring Pressure Units Pounds per square inch (psi) Kilopascals (kPa) Atmospheres (atm) Millimeters of mercury (mmHg)

5. Measuring Pressure Kilopascals: The standard metric unit for measuring pressure. 101.3 kPa is pressure at sea level at 0°C Atmospheres: A convenient unit where the pressure at 0°C at sea level is equal to 1.00 atm. mmHg: A unit based on the amount of liquid mercury that can be pushed up a tall column by atmospheric pressure. 760 mmHg is pressure at sea level at 0°C Pounds per square inch (psi) The unit of pressure used my many industries in the US 14.7 psi is the pressure at sea level at 0°C

6. What does this mean? 760 mmHg = 101.3 kPa = 1 atm = 14.7 psi For every 1 atmosphere there is 760 mmHg What are some other “for every” statements you could write?

7. How to convert between pressure units 3.10 atm  kPa Use equalities to solve. What do you know? Given 3.10 atm What equalities can you use? 1 atm = 101.3 kPa Set up ratios, cross multiply & solve 3.10 atm = 1 atm x 101.3 kPa (cross multiply to solve for x) The answer is 314 kPa

8. STP  Standard Temperature and Pressure  a standard set of conditions for experimental measurements established to allow comparisons to be made between different sets of data.  Temperature = 273 K (0° Celsius, 32° Fahrenheit)  Pressure = 1 atmosphere of pressure (often expressed as “at sea level”)

9. KMT – The Kinetic Molecular Theory Particles of a gas are in Constant Motion, moving Randomly until they Collide with another particle or a container wall. Particles experience Elastic collisions. The Speed of the particles is directly related to the Temperature Pressure of a gas is related to the Number and the Strength of the collisions with the sides of the container wall.