DIFFUSION, STP, AND IDEAL GAS

LAW12-10-09

DIFFUSION

Diffusion – movement of particlesfrom a region of higher density to aregion of lower density; this is caused by

the random motion of molecules

What happens if I release open a container filled with green gas?

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 …

AA

A

A

A

A

B

B

B

BB

C

C

C

In this cylinder, which type of gas molecule will have the highest partial pressure?

Molecule A

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 VariablesPressureTemperatureVolumeNumber 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 downCan approximate most gases as ideal

PV = nRTP = PressureV = Volumen = number of molesR = Ideal Gas ConstantT = temperature

IDEAL GAS CONSTANT R = Ideal Gas Constant

R = 8.314

R = 0.0821 €

L • kPa

mol • K

€

L • atm

mol • K

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 CPressure = 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 atmV = ?n = 1.00 molR = 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?