RSPT 1060 OBJECTIVES. MODULE C Lesson #4 GAS LAWS OBJECTIVES SUPPORTIVE READINGS. Gas Laws. Web Sites

Transcription

1 RSP 060 MODULE C Lesson #4 GAS LAWS OBJECIVES At the end of this module, the student should be able to Define terms associated with gas laws. Define Boyle s Law. Describe the relationship between volume, pressure, mass and temperature. Describe how Boyle s Law can be used to explain normal ventilation. Given appropriate information, use the mathematical formula for Boyle s Law to solve for an unknown. Define Charles s Law. Describe the relationship between volume, pressure, mass and temperature. State a clinical example of when Charles Law is applied in respiratory therapy. Given appropriate information, use the mathematical formula for Charles s Law to solve for an unknown. OBJECIVES SUPPORIVE READINGS At the end of this module, the student should be able to Define Gay Lussac s Law. Describe the relationship between volume, pressure, mass and temperature. Give a clinical example of when Gay-Lussac's Law is applied in respiratory therapy Given appropriate information, use the mathematical formula for Gay-Lussac's Law to solve for an unknown. State the combined gas law. Given appropriate information, use the mathematical formula for the Combined Gas Law to solve for an unknown. State the Universal (Ideal) Gas Law. Egan: Gas Behavior Under Changing Conditions, pgs. 09 Sibberson s Math for RC: Chapter Boyle s Law, pgs. 7 9, Sample Problems Fourth Set. Chapter Charles s Law, pgs. 9 0, Sample Problems Fifth Set. Chapter Gay Lussac s Law, pgs. 0, Sample Problems Sixth Set. Chapter Combined Gas Law, pgs. 6, Sample Problems Seventh & Eighth Set. Chapter Practice Exercises, pgs. 9 3, # 60. Web Sites Gas Laws /airplane/boyle.html Laws describing the behavior of gases. Supported by the Kinetic Molecular heory Six assumptions Applies to most situations. Exceptions to these laws may occur when there is Extremely high pressures Extremely low temperatures

2 Physical Properties Compared in the Gas Laws Gas Law - Summary able amount of matter Pressure he force per unit of surface area (pounds per square inch or psi). Results from molecular collisions. emperature measurement of the degree of molecular activity Volume space occupied by matter For a gas it is the volume of the container because gases will always fill the container. Law: Formula: Constant: Relationship: Rearranged: Boyle s PxV=PxV emperature & Inverse: P = V V=PxV P P=PxV V Charles s V = V Pressure & Direct: = V V=Vx Gay Lussac s P = P Volume & Direct: = P P=Px Combined PxV = PxV Variable V=VxPx Px P=VxPx Vx =PxVx PxV Memory Game What remains constant? Boyle s Law Boyle s = Boiling (emperature constant) Charles s = Charlie watches V. (Pressure constant) Constants: & emperature Measured under Isothermic conditions Constant temperature Difficult to accomplish Gay Lussac s = GV (Volume constant) Gas volume P x V = P x V Opposite of Isothermic: Adiabatic means a varying temperature Boyle s Law Inverse relationship: P x V = P x V As pressure exerted on a gas is increased, volume will decrease. As pressure exerted on a gas is decreased, volume will increase.

3 Boyle s Law NBRC Question Solve for the unknown : P x V = P x V P x V = P x V (both known) (one known & one unknown) You have 3 liters of gas at 770 mmhg. he volume is changed to.5 liters. (he mass and temperature are constant.) Which of the following statements would be true concerning this situation? I. he pressure has increased II. he pressure has decreased III. he pressure is now 94 mmhg IV. he pressure is now 64.7 V. he pressure has not changed Calculation Choose an answer P x V = P x V V = 3 liters of gas P = 770 mmhg V =.5 liters (volume decrease) P =? Rearrange the formula P = P xv = V increase or decrease? I he pressure will increase II he pressure will decrease III he pressure will be 94 mmhg IV he pressure will be 64.7 V he pressure will not change a. I & II b. I & III c. II & III d. II & IV e. V only Practice Problem # Sibberson s Practical Math for RC: Chapter : Boyle s Law, pgs, 7-9, Sample Problems Fourth Set. P x V = P x V V =6.4L P = 70 mmhg V = 4.75L P =? increase or decrease? Rearrange the formula P = P xv = V 3

4 Examples Closed syringe Close off the end of a syringe and pull back. Vacuum is formed with pressure decrease and volume increase. Normal breathing Muscle contraction and inspiration causes decreased pressure in the pleural space and lungs. Decreased pressure yields volume movement into the lungs and increase in volume. emp constant Pressure change = Volume change Charles s Law V V Constants: & Pressure Direct Relationship as temperature increases, volume increases Charles s Law NBRC Question Rearrange the formula to find V V V If you have liters of a gas at 37 C and 75 mmhg and you change the temperature to 68 C without changing the pressure (constant pressure is Charles s Law), what is the new volume of gas? Do you expect the volume to increase or decrease? A B C D E. Liters.8 liters liters.4 liters.6 liters 4

5 emperature Scales Calculation When working with gas laws always convert temperature to Kelvin. Celsius (C) + 73 = Kelvin (K) V V 37 C 73 K 30 K V liters of gas 68 C 73 K 34 K V UNKNOWN increase/decrease Practice Examples Sibberson s Practical Math for RC: Chapter : Charles s Law, pgs, 9-0, Sample Problems Fifth Set. Balloon filled with air Put in refrigerator and it shrinks Put by heater and it expands Pulmonary Function esting Patient exhales warm gas (37 C) into cold spirometer (room temp). Measured gas volume will be less than actual volume in the lungs. Measured volume must be corrected from APS to BPS. Gay-Lussac s Law Constants: & Volume Direct Relationship as temperature increases, pressure increases P P 5

6 Gay-Lussac s Law NBRC Question Rearrange the formula to find P P P You have.5 liters of a gas at 40 C and 750 mmhg pressure. he temperature of the gas is changed to 5 C without changing the volume (constant volume is Gay-Lussac s Law), what is the new pressure of gas? Do you expect the pressure to increase or decrease? A he new pressure will increase by a factor of 5 B he new pressure will increase by a factor of 5 C 47 mmhg will be the new pressure D 74 mmhg will be the new pressure E here will not be a pressure change emperature Scales Calculation When working with gas laws always convert temperature to Kelvin. Celsius (C) + 73 = Kelvin (K) P P P 750mmHg 40 C 73 K 33 K 5 C 73 K 98 K P UNKNOWN increase/decrease Calculation Choose an answer P P A. he new pressure will increase by a factor of 5 B. he new pressure will increase by a factor of 5 C. 47 mmhg will be the new pressure D. 74 mmhg will be the new pressure E. here will not be a pressure change 6

7 Practice Examples Sibberson s Practical Math for RC: Chapter : Gay Lussac s Law, pgs, 0 -, Sample Problems Sixth Set. Gas cylinder Exposure to increased temperatures will cause the pressure in the cylinder to rise Bicycle tires On a hot day the tire pressure will be higher than the pressure on a cold day Automobile tires After driving a car for a while the tire pressure will increase as the tires heat up. Combined Gas Law PV PV is the only constant his formula can replace all previous. emperature & Pressure & Volume Relationships Guidelines Sibberson Math Book page 4 Before doing any calculations Must correct temperature to Kelvin Before doing any calculations Must subtract water vapor Use the emperature & Humidity Chart 7

8 Sibberson Math Book page 5 Set up a chart before you set up your formula P PH O = P PH O = V = V = (convert to K) = (convert to K) = Fill in chart then set up formula: PV PV NBRC Question A gas is at 4 C and 760 mmhg pressure. It occupies a volume of.5 liters. he temperature is decreased to 37 C and the volume decreases to liters. What is the new pressure? (decreased or increased?) Set up the table Change temp. to Kelvin Subtract PH O (if indicated) Rearrange formula Solve for unknown Set up a chart before you set up your formula P PH O = V = P PH O = V = (convert to K) = (convert to K) = Fill in chart then set up formula: PV P V PV P V Practice Problem # page 6 (vapor) Sibberson s Practical Math for RC: Chapter : Combined Law, pgs, - 6, Sample Problems Seventh & Eighth Set. Seventh set is dry gases Eighth set is gases with water vapor On hand is a gas volume of 5.8 L, at a temp. of 3C, and an atmospheric pressure of 7 mmhg, APS. Find the new volume if the gas was measured at SPD. P PH O = V = PV P V P PH O = V = (convert to K) = (convert to K) = 8

9 5. Universal Gas Law Gas Law - Summary able P xv = nr n = Gram molecular weight (mass) R =.4 L (molar volume) All parameters can vary Pressure emperature Volume Used in situations where mass is varying Not used in Respiratory herapy Law: Formula: Constant: Relationship: Rearranged: Boyle s P xv =P xv emperature & Inverse: P = V V =P xv P P =P xv V Charles s V = V Pressure & Direct: = V V =V x Gay Lussac s P = P Volume & Direct: = P P =P x Combined P xv = P xv Variable V =V xp x P x P =V xp x V x =P xv x P xv 9