Gas Laws Flashcards
Empirical gas laws describe…
The 4 quantities that describe the state of a gas:
- Pressure
- Temperature
- Volume
- Number of moles
STP =
Standard temperature and pressure
Standard temperature =
273 K (0 degrees Celsius)
Standard pressure =
1 atm = 760 mm Hg
Standard molar volume—At STP, one mole of (an ideal) gas has a volume of ___
22.414 L (new books may list 22.7 L)
3 empirical gas laws:
- Boyle’s Law
- Charles’s Law
- Avogadro’s Law
Boyle’s Law =
P1V1 = P2V2
Volume is inversely related to pressure (at constant n and T)
Charles’s Law =
V1/T1 = V2/T2
Volume is directly proportional to the absolute temperature (constant n and P)
Avogadro’s Law =
The volume of a gas is directly proportional to the number of gas molecules (constant T and P)
Boyle’s Law = ___ relationship
Volume-Pressure relationship
Boyle’s law forms the basis of the relationship between the three important parameters of a gas…
- Volume
- Pressure
- Temperature
Boyle’s Law—the volume of a fixed sample of gas is inversely related to ___, as long as ___ is constant
Pressure, temperature
Boyle’s law—as pressure increases, volume ___
Decreases
Boyle’s law—as pressure decreases, volume ___
Increases
Boyle’s law is the basis of ___
Breathing
Boyle’s law formula
P1V1 = P2V2
Charles’ work was the basis of ___
The ideal gas law
Charles’ Law is also known as the ___
Law of volumes—describes how gases expand in volume when heated
Charles’ Law states that the volume of an ideal gas is proportional to ___
Its absolute temperature under constant pressure
Charles’ Law changes ___ of gas molecules
Kinetic energy
Charles’ Law—if absolute temperature of a gas doubles, ___ doubles
Volume
Charles’ Law—if temp is halved, volume ___
Halved
Charles’ Law formula
V1/T1 = V2/V2
Kelvin scale for Charles’ Law
K = Degrees Celsius + 273
Charles’ Law—temperature corresponding to V = 0
Must be the coldest possible temperature—this temperature is called absolute zero
Charles’ Law example—cuff volume ___ in an ETT placed in a patient
Increased cuff volume with increased patient body temperature
Can result in increased mucosal pressure and integrity
Concern in pediatric patients; could cause subglottic stenosis
Avogadro—the ___ relationship
Volume-mole relationship
Avogadro’s number =
6.022 x 10^23
Avogadro’s Law—at equal temperatures and pressures, equal volumes of gas contain ___ numbers of particles; the volume of gas is directly proportional to ___, as long as pressure and temperature are held constant
Equal; number of gas molecules
Avogadro’s Law formula
V1/n1 = V2/n2
At STP, one mole of (an ideal) gas has a volume of ___
22.414 L (22.7 L)
Gay-Lussacs Law formula
P1/T1 = P2/T2
Gay-Lussacs Law—pressure is directly proportional to ___ if volume is constant
Temperature
Gay-Lussacs Law—as temperature goes up, pressure ___
Goes up (if volume is constant)
Gay-Lussacs example—N2O cylinder
As gas is released, liquid in tank vaporizes; heat is lost; temperature in cylinder falls and pressure drops (temperature affects pressure on constant volume cylinder)
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
Formula for ideal gas law
PV = nRT
P = pressure V = volume N = number of moles T = absolute temperature R = constant
Ideal gas law—volume is inversely proportional to ___
Pressure
Ideal gas law—volume is directly proportional to ___
Absolute temperature, moles
R =
Universal gas constant
Most common R = (#)
0.08205
R describes the relationship between ___ and ___
Temperature and kinetic energy
The value of R in SI units =
8.314 J/mol/K
Gas density depends strongly on ___ and ___
Temperature and pressure
What is partial pressure?
The pressure exerted by an individual gas in a mixture
Dalton’s law of partial pressures
The total pressure of a mixture of gases is equal to the sum of the partial pressures of the component gases
Relative humidity measures…
The saturation of water in air (mass of water in the air/mass of water that WILL FIT in the air)
Do ideal gases exist?
No
Kinetic molecular theory of gases
Based on the four basic tenets which exactly describe an ideal gas
Assumes that molecules are very small relative to the distance between molecules; the molecules are in constant, random motion and frequently collide with each other and with the walls of any container
Kinetic molecular theory of gases—1) Gases consist of…
Small particles whose volume is negligible compared to the volume of the gas
Kinetic molecular theory of gases—2) Gas molecules are in ___ motion
Constant, random
Kinetic molecular theory of gases—3) The molecules in the sample show a range of kinetic energies, but the average KE depends only on ___
Temperature
Kinetic molecular theory of gases—4) There are no ___ between gas particles, so all collisions are elastic
Attractive or repulsive forces between the gas particles
What is the density of a gas?
D = M/V
Pressure of a gas measures ___
Linear momentum of the molecules
Pressure =
Force/area
Temperature of a gas
Measure of the mean kinetic energy of the gas
The higher the temperature, the ___ motion
Greater the motion
Internal energy
Sum of kinetic and potential energy
Temperature is directly proportional to ___
Average KE
The average KE is the same for gases at the same ___
Temperature
Different gases have the same average KE if…
Their temperatures are the same
Diffusion
Movement of a substance from an area of higher concentration to an area of lower concentration
Effusion
Movement of a gas through a small opening
Graham’s Law of Effusion—The rate of effusion is inversely proportional to ___
The rate of effusion is inversely proportional to the square root of the molecular mass
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 what 4 things?
- Chemical nature of the membrane itself
- Surface area of the membrane
- Partial pressure gradient of gas across the membrane
- Thickness of the membrane
Diffusion rate of a gas is directly proportional to (3)…
- Partial pressure gradient
- Membrane area
- Solubility of gas in membrane
Diffusion rate is inversely proportional to (2)…
- Membrane thickness
- The square root of the molecular weight
Diffusion-limited gas exchange describes 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 gas across the alveolar membrane
Perfusion-limited gas exchange describes the scenario in which 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
Diffusion- and perfusion-limited gas exchange are distinguished by the extent that an alveolar gas’ ___ as blood ___
Partial pressure will equilibrate across the alveolar membrane as blood flows through the pulmonary capillaries
Nitrous oxide perfusion-limited gas exchange
The idea that the partial pressure of nitrous oxide equilibrates rapidly, eliminating the partial pressure gradient across the alveolar membrane long before blood reaches the end of the capillaries. The principle factor limiting blood transport of N2O away from the lungs is the rate of blood flow through the pulmonary capillaries (perfusion-limitation)
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 (4):
- 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 ___ than O2
Larger
CO2 diffuses ___ faster than O2
20x’s — because it is 20x’s more soluble
Equilibration of an inhalational agent occurs in the body when the partial pressure of the gas is ___
The same everywhere
The process by which the fetus receives O2 and drugs is ___
Simple diffusion across a membrane
Diffusion of a gas from alveoli to blood (or back out) requires a difference in ___
Partial pressures
Henry’s Law—the amount of a non-reacting gas which dissolves in liquid is directly proportional to the ___, provided the temperature remains constant
Partial pressure of the gas
Dissolved O2 in blood =
0.003ml/100ml/mmHg partial pressure of O2
Calculate—multiply pp of O2 by 0.003
Dissolved CO2 in blood =
0.067ml/100ml blood/mmHg partial pressure of CO2
Calculate—multiple pp of CO2 by 0.067
The amount of gas dissolved is inversely proportional to ___
Temperature
The colder the liquid, the ___ gas that will dissolve in the liquid
More
Ostwald’s Solubility Coefficient
The quantity of solvent needed to dissolve a quantity of gas at a given temperature and pressure
Ostwald’s solubility coefficient—the higher the coefficient, the ___ gas dissolves in the liquid
More readily (i.e.: blood/gas)
The two phases must be specified
Higher partition coefficient = ___ lipophilicity = ___ potency = ___ solubility
Higher lipophilicity, higher potency, higher solubility
High solubility = ___ anesthetic needs to be dissolved = ___ onset
More anesthetic, slower onset
MAC ___ as blood gas partition coefficient increases
Decreases
Meyer Overton rule
Agents with increased oil solubility have greater potency (d/t a cell’s lipid membranes)
Ideal gases obey gas laws at all ___
Temps and pressures
Do ideal gases exist?
No
Real gases deviate at ___
High pressure and/or low temps
What equation deals with the deviations in real gases?
Vander Waals
Vander Waals relationship assumes that gas molecules have ___ volumes and gas molecules ___ one another
Finite volumes, attract one another
Joule-Thompson Effect—thermodynamic process that occurs when a fluid ___ from high pressure to low pressure at constant enthalpy. Under the right conditions, this can cause ___ of the fluid
Expands, cooling
Examples of the Joule-Thompson Effect—as a cylinder of compressed gas empties, the cylinder ___
Cools
Other examples: how a cryoprobe works, N2O tanks
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
AKA — compression that increases the internal energy of the air by external work done on the air
Adiabatic compression—the increase in temperature of the air during adiabatic compression tends to increase the ___ on account of the ___ in volume alone
Pressure, d/t decrease in volume
Reaction of CO2 in soda lime
CO2 + H2O —> H2CO3
H2CO3 + 2NaOH —> Na2CO3 + 2H2O + heat
Na2CO3 + Ca(OH)2 —> CaCO3 + NaOH
