A Look at some Gases

 

Room Temperature and Pressure = 25 C , 1 atmosphere

Volume at RTP = 24 dm3 

 

So, let's assume that these 3 flasks below are filled with different gases and have a volume of 24dm3. These gases are at room temperature and pressure, rtp. If you weighed all 3 gases, all are exactly 1 mole of each gas!

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Avogadro's Law :

1 mole of every gas occupies the same volume, at the temperature and pressure. At rtp, the volume is 24dm^3. 

 

Avagadro's Law always holds: it doesn't matter if the gas exists as an atom or molecule and it the atoms are large or little. 

 

Molar Volume : the volume occupied by 1 mole of gas.

eg. 24dm3 at rtp

 

 

THE CALCULATION TRIANGLE

 

 

 

 

 

 

 

 

 

 

 

CONVERSION TABLE

 

 

 

 

 

 

 

 

Calculating gas volumes from moles and grams

Example 1:

What volume does 0.15 moles of gas occupy at rtp?

1 mole = 24dm3

0.15 mole = ? dm3 

 

Answer: 0.15 x 24dm3 = 3.6 dm3

                                     = 3600 cm3

 

 

Example 2:

What volume does 16 g of nitrogen occupy at rtp?

Mr of Nitrogen - 28 g 

28g = 1 mole

 

28g / 16g - 1.75

So, 1 mole / 1.75 = 0.57 mole

 

Thus, volume occupied is 0.57 x 24dm^3 = 13.68 dm^3

 

 

CALCULATING GAS VOLUMES FROM EQUATIONS

To answer these questions, you would need an equation to tell how many moles take part and also the usage of Avogadro's Law to figure out the volume.

 

Example 1 :

What volume of hydrogen will react with 24dm^3 of oxygen to form water?

 

Firstly, create a balanced equation.

 

2H2 + O2 ----> 2H2O 

 

This means that 2 moles of Hydrogen reacts with 1 mole of oxygen to get 2 moles of water.

 

Secondly, find the Mr of Hydrogen which is 2. 

 

Since there is 24dm^3 of oxygen, the volume of hydrogen that reacts will be Mr x 24dm^3 

2 x 24dm^3 = 48dm^3

 

Answer: 48dm^3 of hydrogen will react.

 

 

Example 2:

Sulfur burns in air and forms sulfur dioxide. What volume of the gas produced when 1g of sulfur burns?

 

The balanced equation : S + O2 ---> SO2

( 1 mole of Sulfur reacts with 1 mole of oxygen to give 1 mole of sulfur dioxide. )

 

Ar of Sulfur - 32g

So, 1 g of sulfur - 1/32 = 0.03125 moles

 

Since it is in a 1:1 ratio;

0.03125 moles of S gives 0.03125 moles of SO2.

 

Answer: Volume of SO2 produced - 0.03125 x 24dm^3 = 0.75dm^3 or 750cm^3

 

 

 

 

            REMINDER!!! 

 

 

 

        REMEMBER THE FORMULA LINKED FROM CHAPTER 6.1 - 6.4

 

               

 

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