Applied Chapter 12.1 : Characteristics of GasesPresentation Transcript
Chapter 12.1 Characteristics of Gases
Describe the general properties of gases. Define pressure, give the SI unit for pressure, and convert between standard units of pressure. Relate the kinetic-molecular theory to the properties of an ideal gas. Objectives:
Kinetic-Molecular Theory (KMT)
Based on the idea that particles of matter are always in motion. Provides a model of an ideal gas Imaginary gas that perfectly fits all the assumptions of the kinetic-molecular theory. KMT is based on the following 5 assumptions: Gases consist of large numbers of particles that are far apart relative to their size.
Volume of gas particles occupy a volume usually about a thousand times greater than liquid and solid particles.
Collisions between gas particles and between particles and container walls are elastic collisions.
Elastic collisions are ones in which there is no net loss of kinetic energy.
Gas particles are in continuous, rapid, random motion. They therefore possess kinetic energy.
Kinetic energy is the energy of motion.
There are no forces of attraction or repulsion between gas particles.
Think of gas particles as small billiard balls, when they collide , they do not stick together, they bounce apart immediately.
The average kinetic energy of gas particles depends on the temperature.
Higher the temperature, the faster the particles move
Kinetic-molecular theory and the nature of gases Expansion:
Gases do not have definite shape nor volume
The expand to fill container and take it’s shape and volume
Kinetic-moleculartheory Gas particles move rapidly in all directions (assumption 3) without significant attraction or repulsion between them ( assumption 4)
Ability to flow
Liquids and gases are considered fluids because they both flow
Kinetic-moleculartheory Low Density
Density of a gas is 1/1000ththat of liquid or solids.
Animation Kinetic-moleculartheory Particles are so much farther apart in a gaseous state (assumption 1).
Crowding particles closer together.
Kinetic-moleculartheory Gas particles are initially far apart (assumption 1), allowing the particles to be crowded together. Diffusion
Spontaneous mixing of the particles of two substances caused by their random motion.
Kinetic-moleculartheory Random and continuous motion of the molecules (assumption 3) carries them throughout the available space.
Process by which gas particles pass through a tiny opening.
Animation of Effusion Source: http://www.chem.iastate.edu/group/Greenbowe/sections/projectfolder/flashfiles/gaslaw/micro_effusion.html
Pressure To describe a gas fully, there are four measurable quantities Volume Temperature Number of molecules Pressure
Pressure and Force Pressure – defined as the force per unit area on a surface Pressure = force area Use pressure to explain why it is harder to cut this pineapple with the butter knife. How do snow shoes work? How does pressure help us skate?
force N Pressure = Units: area cm2 H0w is a magician able to survive laying on a bed of nails?
Atmospheric Pressure : Blanket of air surrounding earth, exerting pressure
Barometer: Device used to measure atmospheric pressure. At OoC, atmosphere can support 760 mm column of mercury. Units of Pressure: 1 atmosphere or 1 atm millimeters mercury ormm Hg torr (in honor of EvangelistaTorricelli) Pascal, Pa - pressure exerted by a force of one Newton acting on an area of one square meter. Conversions 1 atm = 760 mm Hg 1 torr = 1 mm Hg 1 atm = 760 torr 1 atm = 1.013 25 x 105 Pa 1 atm = 101.3 25 kPa
Standard Temperature and Pressure Scientists have agreed on standard conditions of : 1 atm pressure and O0C Also known as STP Sample Problem 1 The average atmospheric pressure in Denver, Colorado, is 0.830 atm. Express this pressure (a) in mm Hg and (b) in kPa. 760 mm Hg 0.830 atm x (a) = 631 mm Hg 1 atm 101.325 kPa 0.830 atm x (b) = 84.1 kPa 1 atm