Gas Laws Flashcards
Empirical Gas Laws
Describe the 4 quantities that describe the state of a gas
- Pressure
- Temperature
- Volume
- Number of moles
Boyle’s Law
Volume is inversely related to pressure
Forms the basis of the relationship between the 3 important parameters of a gas: volume, pressure, and temperature
Increasing the pressure of a gas at a constant temperature, the volume decreases, and vice versa
breathing
Charle’s Law
AKA: the law of volumes
Volume is directly proportional to temperature
- gases expanded in volume when heated
- his work was the basis of the ideal gas law
cuff volume increases in an ETT placed in a pt bc its warmed by pt
Avogadoro’s Law
The volume-mole relationship
The volume of a gas is directly proportional to the number of gas molecules as long as temp and pressure are constant
Gay-Lussacs Law
Pressure is directly proportional to temperature
-temperature goes up, then pressure goes up if volume constant
Example: N2O. Liquid in a tank. As gas is release, liquid vaporizes. Heat is lost. Temperature in the cylinder falls and the pressure drops
How to remember gas Law
Triangle
Boyles law (corner B), relates to pressure and volume (adjacent sides)
Can These Guys Possibly Be Violinists
Avogadro’s Number
6.022 x 10 the the 23rd
Combined Gas Law
Combining Boyle’s, Charles, and Gay-Lussacs laws
Standard Molar Volume
At STP, one mole (of an ideal) gas has a volume of 22.4L
The Ideal Gas Law
Combines the elements of the empirical gas laws to formulate a state function to completely describe the state of a gas under a given set of conditions
*no such thing as an ideal gas
PV = nRT
P: pressure V: volume -n: number of moles T: absolute temperature R: is a constant -describes the relationship between temperature and kinetic energy
What is standard temperature and pressure?
STP
standard temperature is 0 celsius or 273.17K
Standard pressure is 1 atm, or 1 bar, or 100 kPa
Gas density depends on what?
Temperature and pressure
Can calculate density if you now temperature and pressure
Dalton’s Law of Partial Pressure
The total pressure of a mixture of gases is equal to the sum of the partial pressure of the component gases
The pressure exerted by an individual gas in a mixture is known as its partial pressure
Mole fraction
A way of expressing the relative proportion of one particular gas within a mixture of gases
Divide the number of moles of a particular gas by the total number of moles in the mixture
Relative humidity
Measures the saturation of water in air
Kinetic molecular theory of gases
Assumes that the molecules are very small relative to the distance between molecules. The molecules are in constant, random motion and frequently colliding with each other and with the walls of any container
-Based on four basic tenets which exactly describe an ideal gas
Density of a gas
Sum of he mass of the molecules divided by the volume which the gas occupies
Pressure of a gas
A measure of the linear momentum of the molecules
Temperature of a gas
Measure of the mean kinetic energy of the gas
Internal energy
The sum of the kinetic energy and potential energy
Temperature is __________ proportional to the average kinetic energy
Directly
Graham’s Law of Effusion
The rate of effusion is inversely proportional to the square root of the molecular mass
Diffusion
The movement of a substance from an area of higher concentration to an area of lower concentration
Diffusion rate of a gas is directly proportional to the:
- partial pressure gradient
- membrane area
- solubility of gas in membrane
Diffusion rate is inversely proportional to:
- membrane thickness
- the square root of the molecular weight.
Effusion
The movement of gas through a small opening
The rate of effusion depends on the speed of the molecules
Fick’s Law
The rate of diffusion of a gas across a permeable membrane is determined by the chemical nature of the membrane itself, the surface area of the membrane, the partial pressure gradient of the gas across the membrane, and the thickness of the membrane
Boltzmann constant
Is equal to the ideal gas constant R divined by AN
AN is the number of molecules in a mole
Diffusion-limited Gas Exchange
The scenario in which the rate at which gas is transported away from functioning alveoli and into tissues is principally limited by the diffusion rate of the gases across the alveolar membrane
Perfusion-limited Gas Exchange
The rate at which gas is transported away from functioning alveoli and into tissues is principally limited by the rate of blood flow through the pulmonary capillaries and thus across the alveolar membrane
Fick’s law of diffusion
The rate of diffusion of a substance across unit area (such as a surface or membrane) is proportional to the concentration gradient
Fick’s law of diffusion for gases explains:
- the concentration effect
- the second gas effect
- diffusion hypoxia
- why N2O leads to increase in volume or increase in pressure in gas spaces in the body
CO2 is how much more soluble than O2
20x
Henry’s Law
The amount of a non reacting gas which dissolves in liquid is directionally proportional to the partial pressure of the
gas, provided the temperature remains constant
-permits the calculation of dissolved O2 and CO2 in blood
How much O2 is dissolved in blood?
0.003mL/100mL
How do you calculate the dissolved O2 in blood?
Multiply the partial pressure of O2 by 0.003
How much CO2 is dissolve in blood?
0.067mL/100mL
How do you calculate how much CO2 is dissolved in blood?
Multiply the partial pressure of CO2 by 0.067
Temperature effect
The amount of gas dissolved is inversely proportional to the temperature (the colder the liquid, the more gas that will dissolve in the liquid)
Ostwald’s solubility coefficient
The quantity of solvent needed to dissolve a quantity of gas at a given temperature and pressure
-the higher the coefficient the more readily the gas dissolves in the liquid (blood:gas)
Blood Gas Partition Coefficient
The ratio of the concentration of a compound in one solvent to the concentration in another solvent at equilibrium. It describes how well the gas will partition itself between the two phases after equilibrium has been reached
- higher partition coefficient = higher lipophillicity = higher potency = higher solubility
- higher solubility = more anesthetic needs to be dissolved = slower onset
- MAC decreases as blood gas coefficient increases
Meyer Overton
Agents with increased oil solubility have greater potency
Ideal gases vs real gases
Ideal gases obey gas laws at all temperature and pressures. There are no ideal gases.
Real gases deviate at high pressure and/or low temperatures
- Van der Waals equation deals with this deviation
- Van der Waals relationship assumes that gas molecules have finite volumes and that gas molecules attract one another
Joule-Thomson effect
A thermodynamic process that occurs when a fluid expands from high pressure to low pressure at constant enthalpy. Under the right conditions that can cause cooling of the fluid.
- as a cylinder of compressed gas empties, the cylinder cools*
- Joule’s Cool’s*
Adiabatic Compression
Compression in which no heat is added to or subtracted from the air and the internal energy of the air is increased by an amount equivalent to the external work done on the air.
The increase in temperature of the air during adiabatic compression tends to increase the pressure on account of the decrease in volume alone.
