Diffusion, STP, and Ideal Gas Law

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Diffusion, STP, and Ideal Gas Law. 12-10-09. Diffusion. 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. What happens if I release open a container filled with green gas?.

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### Diffusion, STP, and Ideal Gas Law

12-10-09

Diffusion
• 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

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 …

B

A

C

A

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

A

A

B

B

B

C

A

A

B

C

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
• 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?