Gas Laws TCU- Student.pptx

Gas Laws NRAN 80323 Casey Crow DNP, CRNA Objectives • Properties of Gas • Boyle’s Law • Charles’ Law • Gay-Lussac’s Law • Avogadro’s Number • Universal Gas Law • van der Waal’s Equation • Adiabatic Changes • Dalton’s Law Kinetic Molecular Theory Explains how molecules behave and was created as...

Gas Laws NRAN 80323 Casey Crow DNP, CRNA Objectives • Properties of Gas • Boyle’s Law • Charles’ Law • Gay-Lussac’s Law • Avogadro’s Number • Universal Gas Law • van der Waal’s Equation • Adiabatic Changes • Dalton’s Law Kinetic Molecular Theory Explains how molecules behave and was created as a conceptual framework to encompass the findings of Boyle, Charles, and Gay-Lussac • Basic matter characteristics • Matter is composed of small particles- molecules • Molecules are composed of atoms • Matter can be solid, liquid, or gas Solids: molecules move about slightly and vibrate Liquids: Molecules slide or flow by one another Gases: molecules move linearly, attractive forces between molecules are less than their kinetic energy, move almost completely free of one another Kinetic Molecular Theory Explains how molecules behave and was created as a conceptual framework to encompass the findings of Boyle, Charles, and Gay-Lussac • Generalized assumptions • Molecules have no volume • Gas molecules exert no force on each other, unless they collide • Collisions of molecules with each other, or the walls of the container, do not decrease the energy of the system • Molecules of a gas are in constant and random motion • The temperature of a gas depends on its average kinetic energy, energy is entirely kinetic Gas Laws • All gases obey certain gas laws in terms of 4 physical characteristics Pressure (P) Volume (V) Temperature (T) Amount (n) 3 Gas Laws Boyle’s Charles’ Gay-Lussac’s • T always expressed in K when applying gas laws • n expressed in moles Boyle’s Law • Pressure is inversely proportional to volume • Temperature is constant P1 V1 = P2 V2 Boyle’s Law P1 V 1 = P 2 V2 • Hand-bag ventilation • Squeeze bag, volume decreases • Pressure increases and expands lungs Boyle’s Law P1 V 1 = P2 V2 • Spontaneous Ventilation • Inspire, thoracic cavity expand, diaphragm contracts • Volume increases, pressure decreases, air flows in • Expire, thoracic cavity reduces, diaphragm relaxes • Volume decreases, pressure increases, air flows out P1 V1 = P2 V2 Boyle’s Law • E-cylinder • 5L tank, when full of compressed O2 has a pressure of 2000 psi • Calculate the L of O2 available in a full tank • 2000 psi * 5L = 14.7 psi * V2 • V2 = 2000 * 5 / 14.7 psi • V2 = 680 L Charles’ Law • Volume is directly proportional to temperature • Pressure is constant V1 / T 1 = V 2 / T2 Charles’ Law V1 / T1 = V2 / T2 • If you deliver a ventilated breath of 500 ml volume at 20 degrees C, what is the volume when the breath is warmed to 37 degrees C when it reaches the alveoli? • 500 ml / 293K = V2 / 310K • V2 = 500 * 310 / 293 • V2 = 529 ml Gay-Lussac’s Law • Pressure is directly proportional to temperature • Volume is constant P1 / T 1 = P 2 / T2 Gay-Lussac’s Law P1 / T1 = P2 / T2 • Decrease the temp, kinetic energy is reduced, pressure is reduced • Increase the temp, kinetic energy is increased, pressure is increased • Direct relationship Gay-Lussac’s Law P1 / T1 = P2 / T2 •A full E cylinder is stored outside in winter when the temperature is 0 degrees C and the gauge reads 1950 psi •What will the pressure be when the tank is brought into the pediatric OR where the temperature is 30 degrees C? •1950 psi / 273 K = P2 / 303 K •P2 = 1950 * 303 K / 273 K •P2 = 2164 psi Gas Laws C V B T P G Can These Geeks Possibly Be Violinists? Gas Laws CONSTANT PAY T V LAW CAN BE GOO D RELATIONSHIP DOW N IN THE DEN Avogadro’s Number • Described the relationship between the amount of a gas and the volume of a gas • Equal volumes of all gases at the same temperature and pressure contain equal number of particles • One mole of a gas at Standard Temperature and Pressure (STP) occupies a volume of 22.4L (molar volume) • A mole is equal to the molecular weight of the gas in grams • Avogadro’s Number: the number of molecules in 1 mole of a gas = 6.023 X 10^23 • 1 m of He weighs 4 g, contains 6.023 X 10^23 atoms • 1 m of O2 weighs 32 g, contains 6.023 X 10^23 atoms Avogadro’s Number Grams --------- Moles --------Liters *STP = 0°C / 273°K and 760 mmHg / 100 kPa / 1 atm Avogadro’s Number • Anesthesia practice • Nitrous oxide cylinder contains 3.4 kg N20 (3400 g) • Molecular weight of N2O = 44g (1 mole) • 1 mole occupies 22.4 L at standard temp and pressure • 3400g/44g= 77.27m 77.27mX22.4L= 1730 L • The nitrous oxide volume can be calculated by weighing the cylinder 3400 g ---- mol 77.27 mol ---- 22.4 L 1730 L *STP = 0°C /44 273°Kg and 760 mmHg / 100 mol kPa / 1 atm Universal Gas Law PV = nrT PV =T T/P = V T/V = P • P = pressure • V = volume • n = number of moles • r = constant • (1 atm)(22.4 L) = (1mol) (273K) • r = 0.0821 L atm / mol K • T = temperature van der Waal’s Equation • Gas laws do not account for • Volume of actual molecules • Intermolecular forces (P + n2a / V2)(V / n-b) = rT • a = measure of attraction between molecules • b = volume excluded by a mole of particles • Deviations between ideal gas law and van der Waal’s equation are not clinically significant • Simplicity of ideal gas laws and molecular kinetic theory approximates the behavior of gases used for anesthesia Adiabatic Changes The state of a gas can be altered without allowing the gas to exchange heat energy with its surroundings • Adiabatic processes entail no increase or decrease in a system’s energy • A system possesses X amount of energy (kinetic, friction, heat) • X is reduced to a smaller area will express a greater intensity • X spread over a larger area will express a decreased intensity • These processes do not allow adequate time for entropy (equilibration) Adiabatic Changes • Energy Concentration Effect: • Example: gas cylinder turned compressing a gas quickly will on quickly, pressure in pipes and intensify kinetic energy and gauges rises rapidly, gas is increase temperature compressed adiabatically, and large temperature rise occurs, • Quick compression does not risk of fire allow heat transfer with the • Example: compressed gas environment expands adiabatically, cooling • Energy Dilution Effect (Jouleoccurs as in the cryoprobe Thompson): rapid expansion of a gas lessens kinetic energy and • Example: air compressed in air decreases temperature supply unit, temp of air rises • Quick expansion does not allow become of compression and so a system of cooling is needed heat transfer with the environment Dalton’s Law of Partial Pressures • The total pressure exerted by a mixture of gases is the sum of their individual partial pressures Ptotal = P1 + P2 + P3 • Total pressure of a system is the … additive pressure of +P 4 each individual gas of a mixture • Multiple gases in a mixture will each exert a pressure in proportion to its percentage in the mixture • The total pressure is the sum of individual molecular collisions with the walls of a container Dalton’s Law of Partial Pressures • Allows for calculation of the partial pressure of a gas if the percent concentration is known • Air at sea level • 79% Nitrogen 760 mmHg X 0.79 = 600 mmHg • 21% Oxygen 760 mmHg X 0.21 = 160 mmHg • Allows for calculation of the percent of concentration of gas by dividing the partial pressure of a gas by the total pressure • Air at sea level • 600 mmHg Nitrogen 600 mmHg/760 mmHg = 0.79 = 79% • 160 mmHg Oxygen 160 mmHg/760 mmHg = 0.21 = 21% • Explains hypoxia at high altitude– How? AtmP is 630 mmHg • Do the math Summary • Solving Ideal Gas Law Problems: • Identify what is given, what is asked • Label appropriately: P1, P2, etc • Identify which law applies- which factor is constant • Convert temperature to Kelvin • Do the Math! PV=nrT PV=T V=T/P P=T/V Resources • Basic Physics and Measurement in Anesthesia, Davis & Kenny, Chapter 4 • Nagelhout, Chapter 15 • Physics for Anesthesiologists, Pisano, Chapter 1 Casey.crow@tcu.