Question

When 0.876 g of CaCl2 (110.98 g/mol) is added to 95.0 g of water at 22.4 °C in a ‘coffeecup’ calorimeter, the temperature of the resulting solution increases to 29.7 °C. The specific heat capacity of the solution is 4.184 J/°C·g and the heat capacity of the Styrofoam cup is negligible. A) Is this reaction endothermic or exothermic? How do you know? B) Calculate the molar heat of solution (∆Hrxn) of CaCl2 in water

Answer 1

Answer:

A) Exothermic

B) 367.6 kJ/mol

Explanation:

A) The reaction is exothermic, we know this because the temperature of the resulting solution increased.

B) We use two formulas

1. Q = m*C*ΔT
2. ΔH = Q/mol

So first we calculate the heat Q released into the water:

• Q = 95 g *  4.184 J/°C·g * (29.7-22.4)°C

• Q = 2901.6 J

Now we divide that value by the moles of CaCl₂:

• mol CaCl₂ = 0.876 g ÷ 110.98 g/mol = 7.89x10⁻³mol

• ΔH = 2901.6 J/7.89x10⁻³mol = 367602 J/mol ≈ 367.6 kJ/mol