The Property of Gases – Kinetic Molecular Theory And Pressure
Kinetic Molecular Theory of Gases The word kinetic refers to motion. Kinetic energy is the energy an object has because of its motion. Kinetic Molecular Theory makes assumptions about: ▫ Size ▫ Motion ▫ Energy of gas particles
1.According to the KMT all matter consists of tiny particles that are in constant, random motion Move in a straight line until they collide with other particles or with the walls of the container.
2. Gas particles are much smaller than the distances between them. Most of a gas consists of empty space. Because they are so far apart, there are no attractive or repulsive forces between the gas molecules The motion of one particle is independent of the motion of other particles
3.No kinetic energy is lost when gas particles collide with each other or with the walls of the container (elastic collision) The total amount of kinetic energy remains constant.
4.All gases have the same average kinetic energy at a given temperature Temperature is a measure of average kinetic energy of particles in a sample of matter. Kinetic energy and temperature are directly related The higher the temperature, the greater the kinetic energy
Absolute Zero The greater the atomic and molecular motion, the greater the temperature is of a substance. If all atomic and molecular motion would stop, the temperature would be at absolute zero (0 Kelvin or -273 o C) 273 + _____ o C = _______Kelvin
Diffusion and Effusion Diffusion – describes the movement of one material through another ▫ Particles diffuse from an area of high concentration to low concentration Effusion – gas escapes through a tiny opening. The heavier the molecule, the slower it will effuse or diffuse
Pressure Pressure is the force per unit area Gas pressure is the force exerted by a gas per unit surface area of an object. Gas pressure is the result of billions of collisions of billions of gas molecules with an object Atmospheric pressure (air pressure) results from the collisions of air molecules with objects. The air pressure at higher altitudes is slightly lower than at sea level because the density of the Earth’s atmosphere decreases as elevation increases. Vacuum - Empty space with no particles and no pressure
Measuring Pressure Barometer – an instrument used to measure atmospheric pressure
Measuring Pressure Manometer – an instrument used to measure gas pressure in a closed container
Units of Pressure and STP Average atmospheric pressure is 1 atm STP (Standard Temperature and Pressure) ▫ 1 atm and 0 o C or 1 atm and 273 K
Dalton’s Law of Partial Pressures P total = P 1 + P 2 + P 3 … + P n Dalton’s law of partial pressures states that the total pressure of a mixture of gases is equal to the sum of the pressures of all the gases in the mixture.
Example 1 P total = P O 2 + P CO 2 + P N 2 0.97 atm = P O 2 + 0.70 atm + 0.12 atm P O 2 = 0.15 atm A mixture of O2, CO2, and N2 has a total pressure of 0.97 atm. What is the partial pressure of O2, if the partial pressure of CO2 is 0.70 atm, and the partial pressure of N2 is 0.12 atm?
Example 2 P total = P O 2 + P CO 2 + P CO P total = 0.563 atm + 2.32 atm + 0.599 atm P total = 3.48 atm 235 kPa 1 atm 101.3 kPa = 2.32 atm 455 torr 1 atm 760 torr = 0.599 atm **You first have to put everything in the same units! There is a mixture of CO 2, O 2, and CO in a container. What is the total pressure if the pressure in atm if O 2 is 0.563 atm, CO 2 is 235 kPa, and CO is 455 torr?