Question

When 0.250 moles of KCl are added to 200.0 g of water in a constant pressure calorimeter a temperature change is observed. Given that the specific heat of the resulting solution is 4.184 J g-1 °C-1, the molar heat of solution of KCl is +17.24 kJ/mol, and that we can ignore the small amount of energy absorbed by the calorimeter, the observed temperature change should be Entry field with incorrect answer now contains modified data °C.

Answer 1

Explanation:

Upon dissolution of KCl heat is generated and temperature of the solution raises.

Therefore, heat generated by dissolving 0.25 moles of KCl will be as follows.

             $17.24 kJ/mol \times 0.25 mol$

                = 4.31 kJ

or,             = 4310 J      (as 1 kJ = 1000 J)

Mass of solution will be the sum of mass of water and mass of KCl.

       Mass of Solution = mass of water + (no. of moles of KCl × molar mass)

                                    = 200 g + $(0.25 mol \times 54.5 g/mol)$

                                    = 200 g + 13.625 g

                                    = 213.625 g

Relation between heat, mass and change in temperature is as follows.

                             Q = $mC \Delta T$

where,    C = specific heat of water = $4.184 J/g^{o}C$

Therefore, putting the given values into the above formula as follows.

                     Q = $mC \Delta T$

            4310 J = $213.625 g \times 4.184 J/g^{o}C \times \Delta T$      

              $\Delta T = 4.82^{o}C$

Thus, we can conclude that rise in temperature will be $4.82^{o}C$.