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) the reactionis exothermic

b) The molar heat of solution is 367 kJ/mol

Explanation:

Step 1: Data given

Mass of CaCl2 = 0.876 grams

Molar mass of CaCL2 = 110.98 g/mol

Mass of water = 95.0 grams

Initial temperature of water = 22.4 °C

Final temperature of water = 29.7 °C

Specific heat capacity = 4.184 J/g°C

Since the temperature increases, heat was generated or given off by the reaction. This means the reaction is exothermic.

B) Calculate the molar heat of solution (∆Hrxn) of CaCl2 in water.

q = m*c*∆T

 with m = the mass = 95 grams

with c = the specific heat capacity = 4.184 J/g°C

with ∆T  = The change in temperature = T2- T1 = 29.7 - 2.4 = 7.3

q = 95 *4.184 * 7.3 = 2.9 kJ

Calculate number of moles of CaCl2

Moles CaCl2 = Mass CaCl2 / Molar mass CaCl2

Moles CaCl2 = 0.876 grams / 110.98 g/mol

Moles CaCl2 = 0.0079 moles

Molar ∆Hrxn = 2.9 kJ / 0.0079 moles = 367 kJ/mol

The molar heat of solution is 367 kJ/mol