Gas Laws Chemistry Class

Objectives Define absolute zero Define absolute zero Convert °C to K Convert °C to K Solve problems involving temperature, pressure, and volume changes Solve problems involving temperature, pressure, and volume changes

The gas laws As you saw in yesterdays activity on the computers there is a relationship between pressure, temperature and number of particles. As you saw in yesterdays activity on the computers there is a relationship between pressure, temperature and number of particles. Well look at this more today. Well look at this more today. Lets review what we saw yesterday.. Lets review what we saw yesterday..

Absolute zero Absolute zero is the lowest possible temperature that a material can reach. Absolute zero is the lowest possible temperature that a material can reach. How does molecular motion relate temperature? How does molecular motion relate temperature? What molecular motion would you predict at absolute zero? What molecular motion would you predict at absolute zero?

Absolute zero At absolute zero there is no molecular motion. At absolute zero there is no molecular motion. No substance can ever reach absolute zero. No substance can ever reach absolute zero. Why? Why?

Absolute Zero °C

Degrees Kelvin Absolute zero is defined as 0 Kelvin ( K). Absolute zero is defined as 0 Kelvin ( K). To convert from K to °C use the conversion factor below To convert from K to °C use the conversion factor below K = °C + 273

Sample conversion 1. Convert 0 °C to K 2. Convert 84 °C to K 3. Convert -13 °C to K 4. Convert 84 K to °C

The combined gas law We discussed the combined gas law earlier in this lecture. Now well learn the RULES for the equation. We discussed the combined gas law earlier in this lecture. Now well learn the RULES for the equation. The combined gas law is presented below The combined gas law is presented below

The rules!!! 1. Whenever you solve a combined gas law problem you MUST be sure that the units of pressure and volume are the same on both sides of the equals sign. 2. TEMPERATURE MUST ALWAYS BE IN UNITS OF K!!!

Sample problem A sample of oxygen gas has a volume of mL when its pressure is atm. What will the volume of the gas be at a pressure of atm if the temperature remains constant? A sample of oxygen gas has a volume of mL when its pressure is atm. What will the volume of the gas be at a pressure of atm if the temperature remains constant?

Sample problem A sample of oxygen gas has a volume of mL when its pressure is atm and its temperature is 50 °C. What will the temperature of the gas be at a pressure of atm if the volume is decreased to mL? A sample of oxygen gas has a volume of mL when its pressure is atm and its temperature is 50 °C. What will the temperature of the gas be at a pressure of atm if the volume is decreased to mL?

Break into your groups and solve some problems HAND STUFF BACK

Avogadros law Avagadro found that for a gas at constant temperature and pressure, the volume is directly proportional to the number of moles of gas. Avagadro found that for a gas at constant temperature and pressure, the volume is directly proportional to the number of moles of gas. This is written as This is written as Where V is volume and n is the number of moles, and a is a constant. Where V is volume and n is the number of moles, and a is a constant.

Ramifications It may seem strange but all gasses occupy the same volume if they are under the same pressure and temperature. It may seem strange but all gasses occupy the same volume if they are under the same pressure and temperature. UF 6 has a molar mass of over 300 g/mol yet a mole of it occupies the same volume as a mole of H 2 which has a molar mass of just over 2 g/mol. Well get into how later. UF 6 has a molar mass of over 300 g/mol yet a mole of it occupies the same volume as a mole of H 2 which has a molar mass of just over 2 g/mol. Well get into how later.

The ideal gas law Well look at the laws that weve studied so far: Well look at the laws that weve studied so far: R is the gas constant

The ideal gas law RULES 1. Volume must be in LITERS 2. Pressure must be in ATM 3. n must be in MOL 4. R = Temperature must be in Kelvin