1. Aim: Why do all gases behave in a similar manner? Do Now: 1.Take out a calculator and reference tables. 2.What does the term STP mean? Hint: Check your reference tables.

2. STP is… Standard Temperature = Standard Pressure = These are the ideal conditions to predict the behavior of gases. When we use the combined gas laws, we can predict what will happen to the pressure, temperature or volume of a sample. We can also use STP to predict the number of molecules in a sample of gas.

3. Avogadro’s Hypothesis Equal volumes of gases at the same temperature and pressure contain the same number of molecules. In other words, 1L of CO 2(g) and 1L of H 2 O (g) at STP will both contain the same number of molecules. Avagadro determined this number. At STP, 22.4L of an ideal gas will contain 1mole of the gas.

4. What’s A Mole? A mole is a unit of measurement used by scientists to describe the number of molecules in a sample. One mole of any substance contains 6.02 x 10 23 molecules. That’s 602,000,000,000,000,000,000,000 molecules. We can use this information to predict the number of molecules in a sample of gas at STP (molar gas volume). Remember – The volume of one mole of gas = 22.4L

5. Converting moles to liters Volume of a gas in Liters at STP Number of Moles Divide by 22.4 L Multiply by 22.4 L

6. A Sample Problem A cylinder of O 2 gas occupies a volume of 60.50 L at STP. How many moles of oxygen gas are in the cylinder?

7. Another Sample Problem A cylinder contains 15.85 moles of N 2 gas at STP. What is the volume (L) of the gas?

8. A Third Sample Problem A cylinder contains 1.58 moles of N 2 gas at STP. What is the volume (L) of the gas?

9. Activity/Homework #