A common laboratory reaction is the neutralization of an acid with a base. When 32.8 mL of 0.500 M HCl at 25.0°C is added to 66.3 mL of 0.500 M NaOH at 25.0°C in a coffee cup calorimeter (with a negligible heat capacity), the temperature of the mixture rises to 28.2°C. What is the heat of reaction per mole of NaCl (in kJ/mol)? Assume the mixture has a specific heat capacity of 4.18 J/(g·K) and that the densities of the reactant solutions are both 1.07 g/mL.

Respuesta :

Explanation:

The given data is as follows.

  Densities of both the reactant solutions = 1.07 g/mL.

  Specific heat = 4.18 [tex]J/g^{o}C[/tex]

  Volume of HCl = 32.8 ml

  Volume of NaOH = 66.3 ml

The reaction will be as follows.

      [tex]HCl + NaOH \rightarrow NaCl + H_{2}O[/tex]

Since, density is mass divided by volume. Hence, calculate the mass of HCl as follows.

             Mass of HCl = Density × Volume of HCl

                                   = [tex]1.07 \times 32.8 ml[/tex]

                                   = 35.096 g

Similarly, mass of NaOH will be calculated as follows.

            Mass of NaOH = Density × Volume of NaOH

                                     = [tex]1.07 g/ml \times 66.3 ml[/tex]

                                     = 70.941 g

Therefore, total mass will be as follows.

               Total mass = Mass of HCl + Mass of NaOH

                                  = 35.096 g + 70.941 g

                                  = 106.037 g

Change in temperature will be calculated as follows.

                [tex]\Delta T[/tex] = [tex](28.2 - 25)^{o}C[/tex]

                          = [tex]3.2^{o}C[/tex]

Therefore, calculate the heat of reaction as follows.

                       q = [tex]mC \Delta T[/tex]

                           = [tex]106.037 g \times 4.18 J/g^{o}C \times 3.2^{o}C[/tex]

                           = 1418.35 J

or,                        = 1.418 kJ         (as 1 kJ = 1000 J)

No. of moles of HCl = Molarity × Volume

                                 = 0.5 M × 32.8 ml

                                 = 16.4 mol

No. of moles of NaOH = Molarity × Volume

                                 = 0.5 M × 66.3 ml

                                 = 33.15 mol

So, HCl is the limiting reagent and heat of reaction produces by per mole of NaCl will be calculated as follows.

  Heat released for 1 mole of NaCl = [tex]\frac{1.418 kJ}{16.4 mol}[/tex]

                                                          = 0.0864 kJ/mol

Thus, we can conclude that the heat of reaction per mole of NaCl is 0.0864 kJ/mol.