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Diffusion, STP, and Ideal Gas Law

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Diffusion, STP, and Ideal Gas Law

12-10-09

- 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 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

- 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?

- 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 – 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

- R = Ideal Gas Constant
- R = 8.314
- R = 0.0821

- 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

- 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

- 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

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

- 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?