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Secondary IV • 2yr.


I came across a difficult question:

Balance the following equation. Then, find the rate (in mol/s) of the reaction when 20 mL of HCl takes 30 seconds before reacting and form products. *The reaction takes place at constant temperature and pressure (25 ° C. and 101.3 kPa).



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Explanations (1)

  • Explanation from Alloprof

    Explanation from Alloprof

    This Explanation was submitted by a member of the Alloprof team.

    Team Alloprof • 2yr.


    The first step in solving your problem is to find the stoichiometric coefficients. 

    Several methods are possible. Personally, I prefer to start with the biggest molecules because they generally have the smallest coefficients. In this situation, it is dichloride (Cl2) and water (H2O). If your final product contains two chlorine atoms, then your reagents must also have two chlorine atoms. You have to do the same thing for each molecule and each atoms to get the following answer:


    To complete the problem, you have to use the concepts of ideal gases and the reaction rate. First of all, you have to find the amount of reagent in moles. 

    Then, you have to convert the temperature to absolute temperature (Kelvin) and the volume from mL to L:

    With this information, you can calculate the number of moles you should get the following answer :

    *Be careful! You must pay attention to the units! 


    From this answer, you just have to divide the quantity in moles by the time to give the speed value like this:


    I hope you will find this answer useful!

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