Unit 8 - Gases Chapter 13.1 and Chapter 14

Measurements with gases Pressure – pressure is simply a measure of how frequently, and how hard, particles collide with their container. Units for pressure include: * atmospheres (standard pressure = 1 atm) * kilopascals (standard pressure = 101.3 kPa) * millimeters of Hg (standard pressure = 760 mmHg) * torr (standard pressure = 760 torr) Use the standard values to convert from one unit to the other. 1 atm = 101.3 kPa = 760 mmHg = 760 torr

Conversion example A gas is found to have a pressure of 99.2 kPa. 1. What is this pressure in atm? 2. What is this pressure in mmHg?

Measurements with gases Volume – measure of how much space is taken up. Gas particles are spread far apart. Between the particles, there is empty space. The volume occupied by a gas includes the entire volume occupied by the particles and the empty space between the particles.

Measurements with gases Temperature – temperature is the measure of particle motion. As particles move faster, the temperature increases. Units for temperature include: * Celsius (standard temperature = 0°C) * Kelvin (standard temperature = 273 K)

Temperature K = ºC + 273 ºC -273 100 K 273 373 Always use absolute temperature (Kelvin) when working with gases. ºC -273 100 K 273 373 K = ºC + 273

Kinetic Theory of Gases The Kinetic Theory states that all matter is made up of particles that are in constant motion. For gases, there are a number of assumptions that we use to explain observed properties.

Kinetic Theory of Gases 1. The particles in a gas are considered to be small, hard spheres with an insignificant volume. * Particles are far apart. Compared to the volume the entire gas occupies, the volume of one particle is tiny. * Compare this to jumping into a lake. Does your volume cause the water level to rise?

Kinetic Theory of Gases 2. The motion of the particles in a gas is rapid, constant, and random. * Gas particles move in straight-lines unless they collide with other particles or their container. * Gas particles spread to fill their container regardless of the shape or volume. * Gas particles are independent. Their movement is not affected by other nearby particles.

Kinetic Theory of Gases 3. All collisions between particles in a gas are perfectly elastic. * Particles don’t lose energy when they collide with their container or each other. * The particles continue to move at the same speed as before the collision.

Kinetic Theory of Gases 4. The average kinetic energy (which is related to speed) is directly proportional to the absolute temperature. * On average, particles move faster at higher temperatures. * Not all particles will have the exact same speed. * Gases at the same temperature will have the same average kinetic energy.

Characteristics of Gases Gases expand to fill any container. random motion, no attraction Gases are fluids (like liquids). no attraction Gases have very low densities. lots of empty space

Characteristics of Gases Gases can be compressed. no volume = lots of empty space Gases undergo diffusion & effusion. random motion