Specific heat capacity

Question

When 100 mL of 0.200 M NaCl(aq) and 100 mL of 0.200 M AgNO₃(aq), both at 21.9 °C, are mixed in a coffee cup calorimeter, the temperature increases to 23.5 °C as solid AgCl forms. How much heat is produced by this precipitation reaction? What assumptions did you make to determine your value?

Answer 1

For this type of problem you want to use the equation q = mC∆T

q = heat = ?

m = mass = 100 ml + 100 ml = 200 ml = 200 g assuming a density of 1g/ml (note: this calculation does not include the mass of the reactants and products. In more advanced courses, you may be required to include these additional masses).

C = specific heat = 4.184 J/g/deg assuming the solutions have the same specific heat as water.

∆T = change in temperature = 23.5º - 21.9º = 1.6ºC

Solving for q we have...

q = (200 g)(4.184 J/g/deg)(1.6 deg) = 1339 J

Assumptions that are made:

1. density of solution is 1.0 g/m
2. specific heat of solution is same as for water, i.e. 4.184 J/g/deg
3. no heat is lost to the surroundings and all of it stays in the calorimeter