2 Phases and gas law unit

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11.2 Gas Laws : 

11.2 Gas Laws Chemistry Class

Objectives : 

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

Absolute zero : 

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

Absolute zero : 

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

Slide 6: 

Absolute Zero -273.15 °C

Degrees Kelvin : 

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

Sample conversion : 

Sample conversion Convert 0 °C to °K Convert 84 °C to °K Convert -13 °C to °K Convert 84 °K to °C

The combined gas law : 

The combined gas law We discussed the combined gas law earlier in this unit. Today we’ll apply it to situations with actual numbers. The combined gas law is presented below

The rules!!! : 

The rules!!! 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. TEMPERATURE MUST ALWAYS BE IN UNITS OF °K!!!

Sample problem : 

Sample problem A sample of oxygen gas has a volume of 300.0 mL when its pressure is 0.947 atm. What will the volume of the gas be at a pressure of 0.987 atm if the temperature remains constant?

Sample problem : 

Sample problem A sample of oxygen gas has a volume of 300.0 mL when its pressure is 0.947 atm and its temperature is 50 °C . What will the temperature of the gas be at a pressure of 0.987 atm if the volume is decreased to 200.0 mL?

Break into your groups and solve these problems : 

Break into your groups and solve these problems

Avogadro’s law : 

Avogadro’s law 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 Where V is volume and n is the number of moles, and a is a constant.

Ramifications : 

Ramifications It may seem strange but all gasses occupy the same volume if they are under the same pressure and temperature. UF6 has a molar mass of over 300 g/mol yet a mole of it occupies the same volume as a mole of H2 which has a molar mass of just over 2 g/mol. We’ll get into how later.

The ideal gas law : 

The ideal gas law We’ll look at the laws that we’ve studied so far: R is the gas constant