The Nature of Gases Prentice-Hall Chapter 13.1 Dr. Yager

Objectives  Describe assumptions of kinetic theory as it applies to gases  Interpret gas pressure in terms of kinetic theory  Define the relationship between Kelvin temperature and average kinetic energy

Kinetic Energy Things that are moving have kinetic energy Things that are moving have kinetic energy K.E. = ½mv 2 ; m = mass, v = velocity K.E. = ½mv 2 ; m = mass, v = velocityExample: A 50 kg student is running at 20 m/sec. The student’s kinetic energy is: K.E. = ½(50 kg)(20 m/sec) 2 = 10,000 joules K.E. = ½(50 kg)(20 m/sec) 2 = 10,000 joules This is all done in the MKS system of units.

Kinetic Energy of a Particle  Theory developed by Boltzmann and Maxwell  The energy of a particle and the temperature are related:

Some Average Velocities at 20 o C  H 7078 km/hr  He 5004 km/hr  H km/hr  O km/hr  CO km/hr O 2 molecule traveling at 1771 km/hr will travel from Washington D.C. to Mexico City in 1.9 hrs. O 2 molecule traveling at 1771 km/hr will travel from Washington D.C. to Mexico City in 1.9 hrs. The only way to fly!!! The only way to fly!!!

 Gas consists of tiny hard spherical particles with insignificant volume.  Gas particles are in constant motion.  Gas particles are very far apart.  There are no attractive or repulsive forces between particles.  The motion of one particle is independent of all other particles. Kinetic Theory of Gases

Particles in a gas are in rapid, constant motion. 13.1

Kinetic Theory of Gases  The motion of the particles are rapidrapid constantconstant randomrandom  The motion only changes direction after a collision when particles hit each otherhit each other hit the wall of a containerhit the wall of a container

Gas particles travel in straight-line paths.

The gas fills the container.

 All collisions between particles in a gas are perfectly elastic.  Elastic means that no energy is lost after each collision.  Elastic is like hard metal balls hitting each other. Kinetic Theory of Gases

Gas Pressure  Gas pressure is the result of simultaneous collisions of billions of rapidly moving particles in a gas with an object.  The lack of particles is also known as a vacuum.  The gas pressure you experience every day is atmospheric pressure, caused by the earth’s gravity acting on the air particles.  Atmospheric pressure decreases with altitude.

A barometer is a device that is used to measure atmospheric pressure.

 The SI unit of pressure is the pascal (Pa).  One standard atmosphere (atm) is the pressure required to support 760 mm of mercury in a mercury barometer at 25°C. Gas Pressure Units

A pressure gauge records a pressure of 450 kPa. What is this measurement expressed in atmospheres and millimeters of mercury?

Your Turn What pressure in kPa and atm does a gas exert at 385 mm Hg ?

Kinetic Energy and Temperature Kinetic energy is proportional to temperature: The particles in any collection of atoms or molecules at a given temperature have a wide range of kinetic energies. Most of the particles have kinetic energies somewhere in the middle of this range.

Absolute Zero  Lowest theoretical temperature: C or 0 K C or 0 K  This is where all particle motion ceases to exist!  Lowest temperature ever reached is 0.5 nanokelvin or K

In this vacuum chamber, scientists cooled sodium vapor to nearly absolute zero.

1. According to the kinetic theory, the particles in a gas a.are attracted to each other. b.are in constant random motion. c.have the same kinetic energy. d.have a significant volume.

1. According to the kinetic theory, the particles in a gas a.are attracted to each other. b.are in constant random motion. c.have the same kinetic energy. d.have a significant volume.

2. The pressure a gas exerts on another object is caused by a. the physical size of the gas particles. b. collisions between gas particles and the object. c. collisions between gas particles. d. the chemical composition of the gas.

2. The pressure a gas exerts on another object is caused by a. the physical size of the gas particles. b. collisions between gas particles and the object. c. collisions between gas particles. d. the chemical composition of the gas.

3. The average kinetic energy of the particles in a substance is directly proportional to the a.Fahrenheit temperature. b.Kelvin temperature. c.molar mass of the substance. d.Celsius temperature.

3. The average kinetic energy of the particles in a substance is directly proportional to the a.Fahrenheit temperature. b.Kelvin temperature. c.molar mass of the substance. d.Celsius temperature.