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All About Gases Advanced Chemistry Demonstration #1 Inflating a Balloon Inflating a Balloon Demonstration #2 Imploding Soda Can Demonstration #3 Eggs in a Flask Five Characteristics of Gases Gases expand to fill their containers • Gases are fluid – they flow • Gases have low density • • 1/1000 the density of the equivalent liquid or solid Gases are compressible • Gases effuse and diffuse • Ideal Gases • Ideal gases are imaginary gases that perfectly fit all of the assumptions of the kinetic molecular theory (KMT) • Gases consist of tiny particles that are far apart relative to their size. • Gas particles are in constant, rapid motion. • They therefore possess kinetic energy, the energy of motion • There are no forces of attraction between gas particles • The average kinetic energy of gas particles depends on temperature, not on the identity of the particle. PRESSURE Pressure is the force created by the collisions of molecules with the walls of a container Unit Symbol Definition/Relationship Pascal Pa SI pressure unit 1 Pa = 1 newton/meter2 Millimeter of mercury mm Hg Pressure that supports a 1 mm column of mercury in a barometer Atmosphere atm Average atmospheric pressure at sea level and 0 C Torr torr 1 torr = 1 mm Hg An Early Barometer Pressure is measured with a barometer The normal pressure due to the atmosphere at sea level can support a column of mercury that is 760 mm high Common Units for Pressure • 1 standard atmosphere (atm) = 101.3 kPa (kilopascals) = 14.7 lbs/in2 = 760 mm Hg (millimeters of mercury) = 760 torr Standard Temperature and Pressure (STP) • Often the volume of a gas is needed at “standard conditions” • For scientists, this means “STP” • Standard temperature is 273 K • Standard pressure is 1atm 101.3 kPa = 1 atmosphere (atm) = 760 mm Hg = 29.92 inches Hg = 14.7 lbs/in2 (psi) Gas Conversions Factors • At STP conditions (0°C, 1 atm): • • 1 mole of any gas occupies 22.4 liters of space. Here are the conversion factors: 23 6.02 x 10 22.4 (at STP) 1 mole= __________ particles= _____L At SLC, standard lab conditions, (25°C, 1 atm): • 1 mole of any gas occupies 24.5 L/mol. Here are the conversion factors: 23 6.02 x 10 24.5 (at SLC) 1 mole= __________ particles= _____L Gas Volume to Mole Sample Problem Convert 3 moles of helium to liters (at STP) Gas Laws Robert Boyle Jacques Charles Amadeo Avogadro Joseph Louis Gay-Lussac The Gas Laws When we make changes in a property of a gas, other properties change in a predictable way ◦ Led to the creation of the Gas Laws • • • Avogadro’s Hypothesis Avogadro’s hypothesis states that ________ equal volumes of gases (under the same temp. and pressure conditions) contain _______ equal number of particles. If containers have the same ____, T ____, P and ___, V then they will # of particles regardless of the _________ have the same ____ of the size gas particle. You might think that a small gas molecule would take up ______ less doesn’t space than a large gas molecule, but it ___________ at the same temperature pressure _________________ and ______________!! Avogadro’s Law Volume and Moles As the # of gas particles increase, the volume of a flexible container will increase if the temperature and pressure of the container remain constant ◦ DIRECT relationship Example ◦ Blowing more air into a balloon makes it larger # particles ___,V ___ Gas Laws • Here is the qualitative relationship between the pressure, temperature, and volume of a constant # of gas particles in a container: (1) ___________ Boyle’s Law: At a constant temperature, as the volume of a container __________ decreases the pressure of the container will ___________. increase ↓ P ___ ↑ V___, *Example: Compressing the gas in a flexible container will decrease its volume. _________ Pressure Volume Boyle’s Law Pressure is inversely proportional to volume when temperature is held constant. P1V1 P2V2 Gas Laws (continued) (2) Guy-Lussac’s ____________ Law: At a constant volume, as the temperature of a container __________ increases the pressure of the container will ___________. increase ↑ P ___ ↑ T___, *Example: Heating a rigid container causes the gas inside faster which causes _________ more pressure. to move __________ Be careful! Too much heat will make it explode! Pressure Temperature (K) Gay Lussac’s Law The pressure and temperature of a gas are directly related, provided that the volume remains constant. P1 P2 T1 T2 Temperature MUST be in KELVINS! Gas Laws (continued) (3) ____________ Charles’s Law: At a constant pressure, as the temperature of a container __________ increases the volume of the container will ___________. increase ↑ V ___ ↑ T___, inflate *Examples: Heating a balloon will cause it to ___________. Taking a balloon outside on a cold winter day will cause shrink it to _____________. • If you could keep a gas from condensing, you could cool it off to absolute zero and the zero volume of the gas would be _________! Volume Temperature (K) Charles’s Law The volume of a gas is directly proportional to temperature, and extrapolates to zero at zero Kelvin. (P = constant) V1 V2 T1 T2 Temperature MUST be in KELVINS! The Combined Gas Law • This equation combines all of the previous three laws into one convenient form. Boyles Law: PxV = constant Guy-Lussac’s Law: P .= constant T Charles’s Law: V = constant T = constant • Using the Combined Gas Law P1 x V 1 P2 x V2 = T1 T2 K K (initial conditions) = (final conditions) requires you to have the temperature in _____________ Kelvin units. The pressure and volume units can be anything as long as the initial and final units are the __________. same ______ The Combined Gas Law The combined gas law expresses the relationship between pressure, volume and temperature of a fixed amount of gas. P1V1 P2V2 T1 T2 Combined Gas Law Sample Problem A balloon at a pressure of 4.5 atmospheres, 300 K, and a volume of 35.0 liters is changed to STP conditions. What will the new volume of the balloon become? • • The Ideal Gas Law An equation used to calculate the __________ amount of gas in a container (in units of _________.) moles PV=nRT Kelvin V = _________, Liters n = # of moles The units for T= __________, R = Ideal Gas Constant • The value of R changes depending on the unit of ____________ pressure used in the equation: R = 62.4 (mm Hg)(L)/(mole)(K) R = 8.31 (kPa)(L)/(mole)(K) R = 0.0821 (atm.)(L)/(mole)(K) R = 2.45 (in. Hg)(L)/(mole)(K) The Ideal Gas Law Practice Problems: 1) 6.5 moles of a gas has a pressure of 1.30 atmospheres and it has a temperature of 20˚Celsius. What is the volume of the gas? ( 1.30 ) ( V ) = ( 6.5 ) (0.0821) ( 293 K) V = 120 L 2) How many moles of gas are there in a 7.3 liter balloon with a pressure of 1.11 atm and temperature of 395 K? ( 1.11 ) ( 7.3 ) = ( n ) ( .0821 ) ( 395 K) n = 0.25 moles