Respuesta :
Explanation:
The given data is as follows.
   Total mass of KBr solution (m) = 125 g + 10.5 g
                            = 135.5 g
  Change in temperature (dT) = 24.2 - 21.1 = [tex]3.1^{o}C[/tex]
     Specific heat (C) = 4.184 [tex]J/g^{o}C[/tex]
Hence, heat absorbed will be calculated as follows.
         q = mC dT
           = [tex]135.5 g \times 4.184 J/g^{o}C \times 3.1^{o}C[/tex]
           = 1757.5 J
Therefore, enthalpy change per gram of salt will be calculated as follows.
          [tex]\frac{1757.5 J}{135.5 g}[/tex]
           = 12.97 J/g
So, no. of moles present in 10.5 g of KBr are calculated as follows.
   No. of moles = [tex]\frac{mass}{\text{molar mass}}[/tex]
              = [tex]\frac{10.5 g}{119 g/mol}[/tex]
              = 0.0882 mol
Change in enthalpy will be calculated as follows.
      [tex]\frac{1757.5 kJ}{1000 \times 0.0882 mol}[/tex]
        = 19.93 kJ/mol
Thus, we can conclude that the enthalpy change for dissolving the given salt is 19.93 kJ/mol and 12.97 J/g.
