Solving Gaw Law Problems



A guide to solving chemical math problems with emphasis on the GAS LAWS.

Using an example; Find the final pressure when 7.52 L of a gas at 12.4o C and 102.4 kPa is heated to 56.7o C with a resulting volume of 7.02 L.

Problem analysis

1. Read the problem carefully and then fill out a DATA chart

      P1 = 102.4 kPa             P2 = ? kPa


      T1 = 12.4 oC               T2  = 56.7 oC

         = 285.4 K                   = 329.7 K



      V1 = 7.52 L                 V2 = 7.02 L

This chart organizes the data into initial and final values.

This chart shows the proper units for each value

This chart clearly shows what is being asked in the problem with the correct units for the question.

Note the temperature unit conversions; these should be done immediately.

2. Write the required formula



                 P1V1       P2V2

                ------  =  ------

                  T1         T2


3. Substitute DIRECTLY into the formula. Do not do any manipulation. 

 

                   102.4 x 7.52             ? x 7.02

                   -------------       =    -----------

                      285.4                    329.7


4. Now solve the arithmetic. Solve by cross multiplication or evaluate completely one side then the other; then do a division. 

                  2.698      =      0.02129 x ?






  Now divide to find the question.


                      2.698

                    ----------       =   ?

                     0.02129


5. Write answer with units and finish off with a statement

                    ?  =  126.7 kPa

The final pressure is 126.7 kPa.

























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