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"We live submerged at the bottom of an ocean of air - Torricelli, 1644" Dr.J.Edward Johnson.M.D., D.C.H., Asst. Professor Kanyakumari Govt Medical College & Hospital, Asaripallam, Nagercoil, Tamilnadu, INDIA.

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Molecular Theory Van der Waals forces Lattice (oscillates) All matter is made of tiny particles called atoms. These atoms are in constant motion Brownian motion (random motion). Each particle has kinetic energy. Collisions between particles are perfectly elastic.

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Interface Saturated Vapour Pressure Pressure

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The Gas Laws Introduction 1. Definitions: Pressure = force/area P = F/A 2. Units: Pascal (Pa): 1 Pa = 1 Newton/m2 or 1N/m2 The Pascal is the Standard International Unit of pressure The Newton is the Standard International Unit of force Atmosphere (atm): one atm =101325 Pa Pounds per sq inch (psi): one atm = 14.7 psi or lbs/in2 Torricelli (torr): one atm = 760 torr mmHg: 1 mmHg = 1 torr Millimeters Hg: one atm = 760 mmHg 1 atm = 14.7 psi = 760 mmHg = 101 kPa

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In the Torricellian tube, the atmospheric pressure supports, mercury 760 mm tall

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Pressure P= f/a Pressure is inversely proportional to area 20ml 10ml 1 atm 2 atm

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Anesthesia Machine Examples Pressure Relief Valve Expiratory Valve Pressure-reducing valve AKA pressure regulator Oxygen Failure warning device Pressure P= f/a

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Boyles Law (Pressure – Volume Law) T he volume of a given amount of gas at a constant temperature varies inversely with the pressure P 1 V 1 = P 2 V 2

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Graph of pressure vs. volume for a gas enclosed in a cylinder at constant temperature (Boyle's law)

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Example - Cylinders For example, if we have a cylinder of gas under pressure equivalent to 13,800 kPa (the internal volume or capacity of the cylinder is about 10 liters), how much gas would be available at atmospheric pressure which we will say is about 100 kPa. 13,800 kPa 10 liters AtmosphereCylinder P1 V1 100 kPa P2 V2 ? P 1 V 1 = P 2 V 2 13,800 x 10 = 100 x V2 V 2 = 13,800 x 10 100 V2 = 1380 lts

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Charles Law (Temperature-Volume Law) Gas volume varies directly with temperature at a constant pressure V 1 /T 1 =V 2 /T 2 Remember, always use degrees Kelvin for temperature representation

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Amontons' Law of Pressure-Temperature Gas pressure varies directly with temperature at a constant volume P 1 /T 1 =P 2 /T 2

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Gay-Lussac Law Law of combining volumes The ratio between the volumes of the reactant gases and the products can be expressed in simple whole numbers. STP- 273.15˚ k(0˚C) - 101kPas(760mmHg)

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Pay TV Can Be Good Pay TV Can Be Good Pressure-Volume-Temperature Relationships Pay- T - V - Can Be Good Pressure constant-Charles Temperature constant-Boyles Volume constant-GayLussac

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Avogadro's Law For a given mass of an ideal gas, the volume and amount (moles) of the gas are directly proportional if the temperature and pressure are constant.

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Avogadro's Law Equal volumes of any two gases at the same temperature and pressure contain the same number of molecules. V n (at constant T and P) One mole of any gas contains the same number of molecules (Avogadro's number =6.02×10 23 ) Gram molecule (mass of gas) Same number of molecules in one gram molecule H2 O2 H2O 2H2+O2=2H20

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Ideal Gas Law (Universal Gas Law) Under the same condition of temperature and pressure, equal volumes of all gases contain the same number of molecules. He N2 O2

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Calibration of Vaporizers One mole of Gas At STP Isoflurane 18.45gm O2 O2 + Isoflurane 224 L Mol.wt of Iso – 184.5 184.5 gm of Iso = 1 mol 0.1 mol 2.24 L 2.24 = 1 % 224

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Calculation of volume of Nitrous Oxide gas 3.4kg Mol. Wt of N2O - 44 1 mol = 44 gm 44 gm(1mol) occupies = 22.4 L 3400 gm occupies = 22.4 x 3400 = 1730 L 44

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Combined gas law The combined gas law is a gas law which combines Charles's law, Boyle's law, and Gay-Lussac's law

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Combined gas law

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Daltons Law of Partial Pressures The total pressure exerted by a mixture of gases is the sum of their individual partial pressures P total = P a + P b + P c + etc GAS Partial Pressure (mmHg) InhaledAlveolarExhaled Nitrogen594.70570569 Oxygen160.00103116 CO20.304028 H2O vapor 5.0047 TOTAL760 PARTIAL PRESSURE of AIR

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Daltons Law of Partial Pressures Entanox Cylinders

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What is the partial pressures of O2 and N2O if you are administering a ratio of 70/30? N20 70% X 760 mmHg = 532 mmHg O2 30% X 760 mmHg = 228 mmHg 760 mmHg Would this differ if you were administering anesthesia at Denver General Hospital? N20 70% X 630 mmHg = 441 mmHg O2 30% X 630 mmHg = 189 mmHg 630 mmHg Daltons Law of Partial Pressures Miami = 14.7 psi Denver = 12.2 psiMiami = 760mmHg Denver = 630mmHg

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Adiabatic heating and cooling Adiabatic changes in temperature occur due to changes in pressure of a gas while not adding or subtracting any heat Cryoprobe – N2O or CO2

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Critical Temperature As the substance approaches critical temperature, the properties of its gas and liquid phases converge, resulting in only one phase at the critical point Critical Temp of N2O = 36.5˚C Critical Temp of O2 = -119 ˚C

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