D.I. Mendeleev A.M.Butlerov

The velocity of chemical reactions
Table of content

Solutions and answers on the tasks

  1. The reaction of water formation goes faster.

    For the solution it is not enough simply to compare the weights of formed substances. In fact, the velocity of reaction is a change in the number of moles of reagents or products in unit of volume in unit of time.

    Let's find amounts of substances. n(H2O) = 4,5/18 = 0,25 mol; n(H2S) = 5,1/34 = 0,15 mol.
    The number of moles of formed water (0,25 mol) is more than the number of moles of hydrogen sulfide (0,15 mol). Thus, the water formation reaction is quicker.

  2. The velocity decreases in 4,5 times.

    Let's write down the law of mass action for the given reaction: v = k[A][B]2.
    To compare the velocities during the different moments of time, it is necessary for us to know the concentrations of substances A and B during these moments of time.

    For the initial moment the concentrations are given.

    At the moment when half of substance A will react, [A] = 0,5[A]initial. = 0,5 mol/liter. According to the equation of reaction, the amount of substance B spent is 2 times larger, i.e. 0,5*2 = 1 mol/liter. It means that concentration B becomes equal to 3 - 1 = 2 mol/liter.

    Let's put the numbers in the formula and we shall find v1/v2 = k*1*32/k*0,5*22 = 9/2 = 4,5.

  3. 0,083 minutes

  4. The velocity increases in greater number of times at heating from 0oC up to 11oC.

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