Theories Of Reaction Rates

To find the rate of disappearance of $A$ , we need to relate the changes in concentration of $B$ to $A$ using the stoichiometry of the reaction:

The reaction is:
$2A%20(g)%20%5Crightarrow%204B%20(c)%20%2B%20C%20(g)$

Given:

The concentration of $B$ increases by $5%20%5Ctimes%2010%5E%7B-3%7D$ mol L $%5E%7B-1%7D$ in 10 seconds.

Calculation:

Rate of formation of $B$ :
$%5Ctext%7BRate%20of%20%7D%20B%20%3D%20%5Cfrac%7B%5CDelta%5BB%5D%7D%7B%5CDelta%20t%7D%20%3D%20%5Cfrac%7B5%20%5Ctimes%2010%5E%7B-3%7D%20%5C%2C%20%5Ctext%7Bmol%20L%7D%5E%7B-1%7D%7D%7B10%20%5C%2C%20%5Ctext%7Bs%7D%7D%20%3D%205%20%5Ctimes%2010%5E%7B-4%7D%20%5C%2C%20%5Ctext%7Bmol%20L%7D%5E%7B-1%7D%20%5Ctext%7Bs%7D%5E%7B-1%7D$
From the balanced equation, 4 moles of $B$ are produced for every 2 moles of $A$ consumed. Therefore, the rate of disappearance of $A$ is half the rate of formation of $B$ :
$%5Ctext%7BRate%20of%20disappearance%20of%20%7D%20A%20%3D%20%5Cfrac%7B1%7D%7B2%7D%20%5Ctimes%20%5Ctext%7BRate%20of%20%7D%20B%20%3D%20%5Cfrac%7B1%7D%7B2%7D%20%5Ctimes%205%20%5Ctimes%2010%5E%7B-4%7D%20%3D%202.5%20%5Ctimes%2010%5E%7B-4%7D%20%5C%2C%20%5Ctext%7Bmol%20L%7D%5E%7B-1%7D%20%5Ctext%7Bs%7D%5E%7B-1%7D$

Conclusion:

The rate of disappearance of $A$ is \( 2.5 \times 10^{-4} \, \text{mol L}^{-1} \text{s}^{-1}

Chapter Questions
1 MCQs