 the layer of the atmosphere closest to Earth’s surface where most clouds and weather are located 

 equals force applied per unit area; in SI, pressure is expressed in pascals (Pa) 

International System of Units (SI) 
 the modernized metric system 

 an SI unit that expresses a fundamental physical quantity (such as temperature, length, or mass) 

 an SI unit formed by mathematically combining two or more base units 

 the SI unit of force that is roughly equal to the force exerted by a mass of 100 g at Earth’s surface 

 a push or pull exerted on an object; expressed by the newton (N), an SI unit 

 the SI base unit of length 

 the SI pressure unit; equal to one newton of force applied per square meter, 1 Pa = 1 N/m2 

kinetic molecular theory (KMT) 
 observed gas behavior and gas laws explained by rapidly moving particles (gas molecules) that are relatively far apart and change direction only through collisions with each other or the container walls 

 the pressure and volume of a gas sample at constant temperature are inversely proportional; PV = k 

 the absolute temperature scale, where zero kelvins (0 K) represents the theoretical lowest possible temperature; 0 degrees C = 273 K 

 the lowest temperature theoretically obtainable, which is 0K (zero kelvins), or 273 degrees C 

 the volume of a gas sample at constant pressure is directly proportional to its kelvin temperature; V = kT 

 equal volumes of all gases, measured at the same temperature and pressure, contain the same number of gas molecules 

 the volume occupied by one mole of a substance; at 0 degree C and 1 atm, the molar volume of any ideal gas is 22.4 L 

 the mathematical relationship that describes the behavior of an ideal gas sample, PV = nRT, where P = gas pressure; V = gas volume; n = moles of gas; R = gas constant, 0,0821 L atm/(mol K); and T = kelvin temperature 
