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 #