Ideal Gases

What is an ideal gas?

Its internal energy only relies on kinetic energy - it has no potential energy

It is a theoretical gas that obeys the gas laws and the equation of state for an ideal gas

What are the gas laws

• Boyles Law - at a constant temperature, pressure and volume are inversely proportional

pV = constant

• Charles’ Law - at a constant pressure, volume and temperature are directly proportional

V/T = constant

• Pressure Law - at a constant volume pressure is directly proportional to its absolute temperature

p/T = constant

Explanation of why the 3 gas laws work

Boyles law pV=constant

• as you reduce volume, the particles of gas are closer together

• collide with each other and the container more often

• pressure increases

Charles’ Law V/T = constant

• as you increase temperature, you increase KE

• at a constant pressure, this means the particles move faster and further apart

• volume increases

Pressure Law p/T = constant

• as you increase temperature, particles gain kinetic energy

• at fixed volume, the particles have more energy to move faster and collide

• increasing pressure

Practical: Investigating Boyle’s Law pV = constant

• Using a Bourdon gauge with a sealed tube with air and oil

• At atmospheric pressure, measure the volume the air occupies

• Increase the pressure and remeasure the volume of air

• Repeat this at regular intervals

• Plot a p on 1/V graph

• You should get a straight line

• Temperature must be constant

Practical: Investigating Charles’ Law V/T = constant

1. A capillary tube is sealed on the bottom and has a drop of concentrated sulfuric acid half way up the tube

2. The tube is attached to a ruler and this is placed in a beaker with a thermometer

3. Add near to boiling hot water into the beaker

4. Record the length of the air gap underneath the drop as temperature decreases to room temperature

5. The length should decrease

6. Plot a graph of length/temperature - line of best fit should show a straight line

7. Shows that length is proportional to temperature

8. Volume = pi(r^2)l so volume is proportional to length

9. So volume is proportional to temperature

Ideal Gas equation

pV = NkT

k = bolztmann’s constant = 1.38 x 10^-23 J/K

N = number of molecules in the gas

• combines the gas laws as pV/T = constant

When is the ideal gas equation used?

• ideal gases

• gases similar to ideal (low pressures and high temperatures)