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.

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

"among the transition metal elements, manganese and zinc have a slight lowering of electronegativities. the reason behind this is that the nuclear charges of these elements are slightly weaker than the other transition metal elements due to the way their valence electrons are filled up. both manganese and zinc have their valence electrons filled up to the 4th shell with 1 pair of electrons (4s2) completely occupying it. although the electrons in the 3rd shell (3d) are yet to be paired since the outer most shell is filled up, the ability of the nucleus to attract electrons is lessened. hence,   the electronegativity (or the ability to attract electrons) is lessened."