Physics 9
Gas Laws
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- Describe an application of Boyle's law in anesthesia
- 1) determinging the contents of a tank of gas 2) ventilation
- What are the properties of ideal gases?
- negligible molecular cohesive forces
- What influences the proportionality constant in Boyle's Law?
- 1) mass of the gas, 2) identity of the gas 3) Temperature of the gas
- What is the application of Graham's Law in anesthesia?
- O2 diffuses faster than CO2 in alveolar gas
- Do real gases act like ideal gases?
- Generally, yes.
- What is the risk of the Joule-Thomson effect in anesthesia machines?
- If a gas cylinder is connected to an anesthetic machine is turned on quickly, the pressure i the connecting pipes rises rapidly, the gas is compressed adiabatically -> temp rise -> explosion
- How does adiabatic compression occur
- Since no heat is exchanged with the environment, the energy from the compression must be used in the gas, as in a state change, temperature change, etc.
- Name common anesthetic vapors (above critical temp)
- N2O, CO2, Halothane, and ether
- What is a partition coefficient?
- The ratio of anesthetic concentrations in two phases while at equilibrium (blood-gas, tissue-gas, or tissue-blood)
- What units are gas densities measured in?
- g/L
- What pressure will vaporized anesthetic add to a gas mixture?
- It's saturated vapor pressure
- How does the rate of diffusion relate to the length of the diffusion path?
- They are indirectly proportional
- What is Henry's Law?
- The solubility of a gas in a liquid at a particular temp is proprtional to the partial pressure of the gas overlying the liquid (assuming the gas does not chemically react w/ the liquid)
- What is Fick's law of diffusion
- Rate of transport of substance (in moles/second) = -DAG, where D is the diffusion coefficient, A is area of diffusion path, and G is the concentration gradient
- What gas best obeys the ideal gas laws?
- H2 - a hydrogen thermometer is used for the international temperature scale
- What does temperature do to gas solubility in a liquid?
- Increasing temperature generally increases solubility
- In Boyle's law, how are P and V related?
- They are inversely proportional
- What is the universal gas law?
- PV=nRT (with P as the absolute pressure, T as the absolute temperature, n=# of moles)
- According to Gay-Lussac's Law, how does a 1 C rise in temperature affect the pressure?
- It rises by 1/273rd of the pressure of the gas at 0C
- What is Dalton's Law?
- If a mixture of gases is contained in a given volume at a given temperature, the total pressure of the mixture is equal to the sum of the pressures which the gases would exert if stored individually at the same volume and temperrature; The ratio of the partial pressures on any component to the total pressure equals the ratio of its partial volume to the total volume
- What is Gay-Lussac's law?
- P/T=k
- In a gas cylinder, what universal gas law values are constant? What does this imply?
- n, R and T are constant; Therefore, P is proportional to n (but this only works if the cylinder contains only a gas)
- When a gas is liquefied, is the pressure gauge an accurate measure of its contents?
- No.
- What is Graham's Law?
- The rate of diffusion of gases are inversely proportional to the square roots of their densities/molecular weights
- Which gases does Gay-Lussac's law apply to?
- 1) substances which remain gases (don't condense to liquids) under high pressure.
- What is the Joule-Thomson effect
- The temperature of a gas falls when it expands without doing any work (e.g. gas at constant pressure through a small orifice)
- What is the difference between a gas and a vapor
- A gas is above its critical temperature; a vapor is below it (i.e. it may be recompresed to form a liquid)
- What is Boyle's Law?
- P1V1=P2V2=k (where P=total [not gauge] pressure, and k is a proportionality constat ant)
- Name 2 gases above their critical temperature at room temp
- O2 and N2
- What is an ostwald solubility coefficient (lamda)
- The ratio of concentration of gas in solution to that in gas phase
- What is critical temperature?
- The temperature above which a substance cannot be liquefied no matter how much pressure is applied?
- How is a concentration gradient calculated?
- Chigh-Clow/distance
- What is Charles's Law?
- V/T=k
- What is the pressure in a tank of gas when the gauge reads zero
- The same as the external pressure (=no pressure gradient=no flow)
- What is the thermal expansion constant for all gases, and what does this mean?
- 1/273.16 (for each degree they drop, their volume drops by 1/273rd of the pressure at 0C if the pressure is kept constant)
- What is Avogadro's number?
- 6.022 x 10^23, the number of atoms in a mass equal to the gram molecular weight of the substance
- What is entonox?
- A 50:50 mixture of O2 and N2O
- What determines the proportionality constant in Gay-Lussac's Law?
- 1) mass 2) identity 3) pressure
- What is diffusion?
- The spreading out/net movement of a substance from a region of high concentration to a region of low concentration
- What kinds of gases do the gas laws apply to?
- Ideal gasses
- How does the concentration gradient relate to the rate of diffusion?
- They are directly proportional
- How does a cryoprobe work?
- Gas is forced through a capilary tube. As it expands adiabatically, it cools and freezes the lesions.
- What is the application of diffusion rates to anesthesia?
- Diffusion of volatile anesthetics are similar to CO2 uptake, which occurs nearly instantaneously, and diffusion times may therefore be ignored.
- What is the triple point?
- The point where the vapor, liquid and solid phases are all in equilibrium (in a phase diagram, where all the lines meet)
- How are V and T related by Charles's Law?
- They are directly proportional