2 The Nature of Gases Gases expand to fill their containers Gases are fluid – they flowGases have low density1/1000 the density of the equivalent liquid or solidGases are compressibleGases effuse and diffuse
3 1) Which statement about atmospheric pressure is false? A) As air becomes thinner, its density decreases.B) Air actually has weight.C) With an increase in altitude, atmospheric pressure increases as well.D) The colder the air, the lower the atmospheric pressure
4 Ideal Gases Ideal gases are imaginary gases that perfectly fit all of the assumptions of the kinetic molecular theory.Gases consist of tiny particles that arefar apart relative to their size.Collisions between gas particles and betweenparticles and the walls of the container areelastic collisionsNo kinetic energy is lost in elasticcollisions
5 Ideal Gases (continued) Gas particles are in constant, rapid motion.They therefore possess kinetic energy, theenergy of motionThere are no forces of attractionbetween gas particlesThe average kinetic energy of gasparticles depends on temperature, noton the identity of the particle.
6 Pressure Pressure is the force created by the collisions of molecules with the walls of a containerUnitSymbolDefinition/RelationshipPascalPaSI pressure unit1 Pa = 1 newton/meter2Millimeter of mercurymm HgPressure that supports a 1 mm column of mercury in a barometerAtmosphereatmAverage atmospheric pressure at sea level and 0 CTorrtorr1 torr = 1 mm Hg
7 2) A gas at a pressure of 10.0 Pa exerts a force of __________ N on an area of 5.5 m2 B) 0.55C) 5.5D) 1.8E) 18
8 Standard Pressure 1 standard atmosphere (atm) 101.3 kPa (kilopascals) 14.7 lbs/in2760 mm Hg (millimeters of mercury)760 torr
9 3) A pressure of 1.00 atm is the same as a pressure of __________ of mm Hg. A) 193 B) 101 C) 760 D) 29.9 E) 33.0
10 Measuring Pressure The first device for measuring atmospheric pressure was developed by Evangelista Torricelliduring the 17th century.The device was called a “barometer”Baro = weightMeter = measure
11 An Early BarometerThe normal pressure due to the atmosphere at sea level can support a column of mercury that is 760 mm high.
12 4) In a Torricelli barometer, a pressure of one atmosphere supports a 760 mm column of mercury. If the original tube containing the mercury is replaced with a tube having twice the diameter of the original, the height of the mercury column at one atmosphere pressure is __________ mm.A) 380B) 760C) 1.52x103D) 4.78 x 103E) 121
14 Standard Temperature and Pressure “STP” Either of these:273 Kelvin (273 K)0 CStandard Temperature and Pressure “STP”And any one of these:1 atm101.3 kPa14.7 lbs/in2 (psi)760 mm Hg760 torr
15 A) a gas is made up of molecules 4) One significant difference between gases and liquids is that __________.A) a gas is made up of moleculesB) a gas assumes the volume of its containerC) a gas may consist of both elements and compoundsD) gases are always mixturesE) All of the above answers are correct.