If 4.05 g of KNO₃ reacts with sufficient sulfur (S₈) and carbon (C), how much P-V work will the gases do against an external pressure of 1.00 atm given the densities of nitrogen and carbon dioxide are 1.165 g/L and 1.830 g/L, respectively, at 20°C?

Respuesta :

Explanation:

Chemical reaction equation for the given reaction is as follows.

     [tex]2KNO_{3}(s) + \frac{1}{8}S_{8}(s) + 3C(s) \rightarrow K_{2}S(s) + N_{2}(g) 3CO_{2}(g)[/tex]

Therefore, we will calculate the number of moles of [tex]KNO_{3}[/tex] as follows.

    No. of moles = [tex]\frac{mass}{\text{molar mass}}[/tex]

                          = [tex]\frac{4.05 g}{101.1 g/mol}[/tex]

                          = 0.04 mol

Number of moles of nitrogen gas formed is calculated as follows.

    No. of moles = [tex]\frac{1}{2} \times \text{no. of moles of KNO_{3}}[/tex]

                          = [tex]\frac{1}{2} \times 0.04 mol[/tex]

                          = 0.02 mol

Mass of [tex]N_{2}[/tex] gas formed will be calculated as follows.

               No. of moles × Molar mass of [tex]N_{2}[/tex]

              = [tex]0.02 mol \times 28.0 g/mol[/tex]

              = 0.56 g

Now, the number of moles of [tex]CO_{2}[/tex] formed is as follows.

              = [tex]\frac{3}{2} \times 0.04[/tex]

              = 0.06 mol

Hence, mass of [tex]CO_{2}(g)[/tex] formed will be as follows.

              [tex]0.04 mol \times 44 g/mol[/tex]

               = 1.76 g

Volume  of [tex]N_{2}(g)[/tex] is calculated as follows.

               Volume = [tex]\frac{mass}{density}[/tex]

                             = [tex]\frac{0.56 g}{1.165 g/L}[/tex]

                             = 0.48 L

And, volume of [tex]CO_{2}[/tex] is calculated as follows.

                 Volume = [tex]\frac{mass}{density}[/tex]

                             = [tex]\frac{1.76 g}{1.830 g/L}[/tex]

                             = 0.96 L

Let us assume that the volume of solids are negligible. Therefore, total volume will be as follows.

           [tex]\Delta V[/tex] = (0.48 L + 0.96 L)

                           = 1.44 L

Relation between work, pressure and volume is as follows.

          w = -[tex]P_{ext} \times \Delta V[/tex]

              = -[tex]1.00 atm \times 1.44 L[/tex]

              = -1.44 atm L

As 1 tm L = 101.3 J. So, convert 1.44 atm L into joules as follows.

             [tex]1.44 \times 101.3 J[/tex]

               = 145.87 J

Thus, we can conclude that the given gases will do 145.87 J of work.