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.
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.
Avogadro’s Hypothesis • Equal volumes of gases at the same temperature
and pressure contain the same number of molecules.
• In other words, 1L of CO2(g) and 1L of H2O(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.
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 1023 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
Converting moles to liters
Volume of a gas in Liters
at STPNumber of Moles
Divide by 22.4 L
Multiply by 22.4 L
A Sample Problem
• A cylinder of O2 gas occupies a volume of 60.50 L at
STP. How many moles of oxygen gas are in the cylinder?
Another Sample Problem
• A cylinder contains 15.85 moles of N2 gas at STP.
What is the volume (L) of the gas?
A Third Sample Problem • A cylinder contains 1.58 moles of N2 gas at STP.
What is the volume (L) of the gas?
Activity/Homework #