1. CHARLES’ LAW [Gay-Lussac’s Law]

§ Law stating that at constant pressure the volume of a given mass of gas varies directly with the absolute temperature

§ [given mass & pressure]

§ Eg: Hot air balloon (constant pressure scenario): an increased temperature of gas —> increased gas volume —> reduced density of gas

2. BOYLES’ LAW

§ An ideal gas law

§ Gives a relationship between pressure and volumes of gases

§ Law stating that the product of the volume and pressure of a gas compressed at a constant temperature remains constant

§ PV = constant [given mass & temperature]

§ ie: when the temperature is constant, the pressure of the gas varies inversely with its volume:— if the volume of a gas is reduced, the gas molecules will be compressed and the pressure will rise

or

Eg: (constant temperature scenarios)

1) Increased volume of chest —> reduced pressure —> flow of air into chest

2) Reduced volume in cylinder during piston compression —> increased air pressure within cylinder

3. Combined CHARLES’ LAW & BOYLES’ LAW

§ A perfect gas always obeys the laws of Boyle & Charles; by combining these two laws to give the equation of a perfect gas

(which is an ideal gas law)

4. DALTON’s LAW [of partial pressures]

§ An ideal gas law

§ Law stating that the total pressure exerted by a mixture of gases is the sum of the pressures exerted independently by each gas in the mixture

§ [Where there are 2 gases: there are N1 molecules of gas 1 & there are N2 molecules of gas 2]

§ Further, the pressure exerted by each gas [its partial pressure] is directly proportional to its percentage in the total gas mixture

§ Eg:What is the partial pressure of oxygen at sea level?

§ = 21% x 760 mmHg = 159 mmHg

5. IDEAL GAS (Perfect Gas)

§ A gas in which the attraction between the molecules can be regarded as negligible & the volume of the molecules is small compared with the space they inhabit

§ Real gases approximate well in characteristics to ideal gases

6. IDEAL GAS LAW

P= pressure of gas in atm

V= volume of gas in L

n= number of moles of the gas

T= temperature of the gas in K

R= a constant for all gases, for all conditions of n, P, V, T

Is a universal law, it holds for all gases including mixture of gases at any temperature, pressure, volume or amount as long as they are ideal gases

7. GAS CONSTANT

§ R= a constant for all gases, for all conditions of n, P, V, T

§ We can determine what the constant is by using the fact that 1 mole at STP occupies 22.4 litres

Thus R (universal gas constant) = 0.0821 L·atm/mole·K

8. HENRY’S LAW

§ An ideal gas law

§ Law stating that the solubility of a gas in a liquid is proportional to the pressure of the gas if the temperature is constant and the gas does not react chemically with the liquid

§ When a mixture of gases is in contact with a liquid, each gas will dissolve in the liquid in proportion to its partial pressure

§ Thus the greater the concentration of a gas in the gas phase, the more and faster will the gas dissolve in the liquid

§ At equilibrium, the partial pressures in both liquid and gas are the same

§ The concentration of a gas in a solution is not only determined by its pressure but also by the solubility coefficient of the gas

§ The more soluble a gas is in the solvent in question, the faster it well diffuse in that solvent

§ Carbon dioxide is physically attracted to water molecules; when molecules are attracted, far more of them can become dissolved without building up excessive pressure in solution

§ Carbon dioxide is approximately 24 X more soluble in plasma than oxygen

§ Henry’s law: Concentration of dissolved gas = pressure x solubility coefficient

9. AVOGADRO’S LAW

§ Law stating that equal volumes of all gases at a given temperature and pressure contain the identical number of molecules

10. GRAHAM’S LAW

§ Law stating that the rate of diffusion of gases is in inverse proportion to the square root of its molecular weight, ie: lighter gases diffuse faster than heavier gases

§ Oxygen — MW = 32 —> diffusion coefficient = 5.6

§ Carbon dioxide —MW = 44 —> diffusion coefficient = 6.6

11. COMBINED GRAHAM’S & HENRY’S LAW

§ If combine the effects depicted by Graham (lighter gases diffuse faster than heavier gases; Oxygen diffusion coeff: 5.6; Carbon dioxide diffusion coeff: 6.6) with that of Henry’s law (the more soluble the gas in the solution the faster will it diffuse; Carbon dioxide is approximately 24 X more soluble in plasma than oxygen) Carbon dioxide will diffuse about 20 times faster than oxygen

§ This has physiological relevance as although the diffusion gradient for carbon dioxide via the alveolus is much less than for oxygen, the greater ability of carbon dioxide to diffuse more than adequately compensates

§ The diffusion coefficient (rate of diffusion through a give area for a given distance & pressure difference) for any gas is proportional to where S is the solubility of the gas

§ MW is the molecular weight of the gas