Unit+5+-+Gases

**Characteristics of a gas:** **Units of volume for gas:** 1 L = 10^3 cm^3 = 10^-3 m^3
 * __Gases__**
 * high kinetic energy
 * no fixed volume or shape
 * rapid movement

**Units of matter for gas:** n = # of moles, m = MM x n (m = mass in grams) **Units of temperature for gas:** K = degrees C + 273 **Units of pressure for gas:** 1 atm. = 760 mmHg = 1.013 bar = 101.3 kPa

**Ideal Gas Law:** PV = nRT P = pressure V = volume n = # of moles R = constant (0.0821 L x atm/ mol x K) T = temperature

**Gas law calculations:** Kinetic Theory of Gases: **gases in motion - changes in temperature and pressure** 4 Assumptions of the Molecular Model of Gases:** **Kinetic Energy Formula:**
 * Always Final/Initial**
 * gases are mostly empty space
 * gas molecules are in constant chaotic motion
 * collisions are elastic [[image:reich-chemistry:all.gif width="268" height="324" align="right"]]
 * gas pressure is caused by collisions of molecules with the walls of the container

E = 3RT/2N

E = Kinetic Energy N = Number of molecules T = Temperature (Kelvin) R = Constant All gases have the same value of Kinetic Energy as a given temperature.
 * Translational Energy is directly proportional to T, temperature.**

**Average Velocity formula:** u = (3RT/MM) ^ 1/2 u = velocity MM = molar mass T = temperature R = 8.31 x 10^3

Average speed, u, is inversely proportional to the square root of MM
 * Average speed, u, is directly proprtional to square root of absolute temp.**

**diffusion:** gases move from higher to lower concentration **effusion:** flow of gas molecules of low pressure through tiny pinholes

rate A / rate B = (MM A/ MM B) ^ 1/2

**Graham's Law**: effusion of gases

- genrally, the closer a gas is to the liquid state, the more it will deviate from the gas law. - deviations from the ideal gas law arise because it neglects 2 factors: 1. gas molecules occupy a finite volume 2. gas molecules attract each other

D=M/V = g/mL

MM= g/mol

(grams is a common variable)

**Total Pressure of gas mixture:** Ptot = Pa + Pb

Pa = Xa Ptotal

**partial pressure:** (Pa +Pb) the pressure a gas would exert if it occupied the entire volume by itself.media type="custom" key="9721382"media type="custom" key="9721410"