Diffusion, STP, and Ideal Gas Law 12-10-09

Diffusion What happens if I release open a container filled with green gas? Diffusion – movement of particles from a region of higher density to a region of lower density; this is caused by the random motion of molecules

Dalton’s law of partial pressures Dalton’s Law of Partial Pressure – the total pressure of a mixture of gases is equal to the sum of the partial pressures of the component gases Ptotal = PA + PB + PC … B A C In this cylinder, which type of gas molecule will have the highest partial pressure? A A A B B C B A A B Molecule A C

Practice Partial pressures If the partial pressure of A is 6 atm (PA = 6), the partial pressure of B is 5 atm (PB = 5), and the partial pressure of C is 3 atm (PC = 3), what is the total pressure of the container?

Derive ideal gas law Variables Pressure Temperature Volume Number of Molecules (Moles) What happens to the pressure when we change these? Increase Temperature = Increase Pressure Increase Volume= Decrease Pressure Increase Moles = Increase Pressure

Ideal gas law Ideal Gas – gas in which molecules keep the exact same speed after collisions. In other words, friction does not slow them down Can approximate most gases as ideal PV = nRT P = Pressure V = Volume n = number of moles R = Ideal Gas Constant T = temperature

Ideal gas constant R = Ideal Gas Constant R = 8.314 R = 0.0821

Review: celsius and kelvin Celsius to Kelvin TK = TC + 273 Kelvin to Celsius Tc = TK - 273 The temperature in Kelvin is always bigger than the temperature in Celsius!! TK > TC

Standard temperature and pressure Because gases are easily affected by temperature and pressure changes, we need a standard pressure and temperature to refer to Standard Temperature and Pressure (STP) Temperature = 0 degrees C Pressure = 1 atm

Standard Temperature and Pressure & Ideal gas law Let’s use PV=nRT to find the volume of 1.00 mol of an ideal gas at STP. P = 1 atm V = ? n = 1.00 mol R = 0.0821 T = 0 degrees celsius + 273 Kelvin = 273 Kelvin

More ideal gas Problems What pressure has a container with 1.20 moles of gas, 14.88 L, and 25 degrees Celsius?

More Ideal Gas Problems A balloon has a volume of 15.9 L, 149 kPa, and a temperature of 28 degrees C. How many moles of gas are in the balloon?