Lecture 2.2: Physics of Gases

Question 1

What is the Role of The Respiratory System?

Answer 1

• Serves to ensure that all tissues receive the oxygen they need
• And can dispose of the CO2 they produce
• Blood carries gases to and from tissues
• Lungs exchange with atmosphere

Question 2

What is the Kinetic Theory of Gases?

Answer 2

• Gases are a collection of molecules moving around a space
• Pressure is generated by collisions of molecules with the walls
• The more frequent and harder the collisions the higher the pressure

Question 3

How to calculate Pressure?

Answer 3

• Pressure = Force / per unit area
• i.e. 1 Newton (N) of force /square metre (m2) = 1 Pascal (Pa)

Question 4

What other way can Pressure be expressed?

Answer 4

Pressure may also be expressed in mmHg (e.g. Blood Pressure of 120/80 mmHg),

Question 5

How much is 1kPa in mmHg

Answer 5

7.5 mmHg

Question 6

How much is 100mmHg in kPa?

Answer 6

13.3kPa

Question 7

How much is 1 standard atmosphere in mmHg and kPa?

Answer 7

• 760 mmHg
• 101.1 KPa

Question 8

What is Boyle’s Law?

Answer 8

• Pressure inversely proportional to volume
• If a given amount of gas is compressed into a smaller volume molecules will hit
the wall more often and pressure will rise

Question 9

What is Charles’s Law?

Answer 9

• Kinetic energy of molecules increases with temperature
• As temperature increases molecules hit walls more often so pressure increases
• Pressure proportional to absolute temperature
• Scale starts at -273 deg C absolute zero

Question 10

What is the Universal Gas Law?

Answer 10

• P.V=R.T
• Allows calculation of how volume will change as pressure and temperature
changes

Question 11

What are Partial Pressures?

Answer 11

• In a mixture if gases molecules of each type behave independently
• They don’t chemically interact
• So each gas exerts a partial pressure
• Calculated as the same fraction of the total pressure as the volume fraction of
the gas in the mixture

Question 12

What is Saturated Vapour Pressure?

Answer 12

• In biological systems gas mixtures always in contact with water
• So water molecules evaporate gas molecules dissolve
• Vapour pressure
• Depends only on temperature
• -6.28 kPa at 37 deg C

Question 13

The amount of gas which enters the liquid to establish a particular
tension is determined by………..?

Answer 13

Solubility

Question 14

What is the Equation to calculate Content?

Answer 14

Content = Solubility x Tension