Chemistry

Chemical Kinetics (continued)


Average speed

The average velocity of a chemical reaction can be given by the ratio of concentration change to reaction time.

Follow the formula and then the explanations.

Where:
Vm = average velocity (mol / L / s)
concentration range (mol / L)
time variation (s, min)
module (result must be positive, speed must be positive)

Units may vary.

Example: Note the transformation of acetylene to benzene:

The average velocity (up to the final process) or partial velocity can be calculated. Dice:

C2H2 (mol)

3,5

2,7

2,0

1,5

0,9

t (min)

0

1

2

3

4

  • Calculation of speed after 4 minutes:

 
    
   

  • Speed ​​calculation between 1 and 2 minutes:


 

The average velocity of a chemical reaction may also be related to the disappearance reaction and the onset reaction, as follows:

The units can be:

Knowing the information about one of the reaction participants, we can calculate the speed of the other participants and even the average reaction speed.
Take the case of ammonia synthesis:

Dividing the velocity calculated for either participant by its own stoichiometric coefficient will result in the same calculation as the other participants.

Where:

These calculations can also be made by rule of three.