Consider the dissolution of CaCl₂: CaCl₂(s) → Ca²⁺(aq) + 2Cl⁻(aq) ∆H = -81.5 kJ/mol A 15.0-g sample of CaCl₂ is dissolved in 145 g water with both substances at 25.0°C. Calculate the final temperature of the solution assuming no heat loss to the surroundings and assuming the solution has a specific heat capacity of 4.18 J/°C･g.

Answer : The final temperature of the solution is,

Explanation :

First we have to calculate the heat produced.

where,

= enthalpy change = 81.5 kJ/mol

q = heat released = ?

m = mass of = 15.0 g

Molar mass of = 110.98 g/mol

Now put all the given values in the above formula, we get:

Now we have to calculate the final temperature of solution in the calorimeter.

where,

q = heat produced = 11.0 kJ = 11000 J

m = mass of solution = 15.0 + 145 = 160.0 g

c = specific heat capacity of water =

= initial temperature =

= final temperature = ?

Now put all the given values in the above formula, we get:

Thus, the final temperature of the solution is,

o conteúdo de calor de um sistema é igual à entalpia apenas para um sistema que é constante