What is the enthalpy change (ΔH) associated with the reaction as written?

Question

Full question:

An amount of solid BaCl₂, 20.8g. is dissolved in 100g of water in a coffee-cup calorimeter by the reaction: BaCl₂ (s) ---> Ba²⁺(aq) + 2Cl^-(aq)

The water is originally at 25oC and after the reaction, the temperature of the solution is 26.6^oC. What is the enthalpy change (ΔH) associated with the reaction as written? (C_s=4.04J/(g^oC) for the solution) (in joules)

Answer 1

BaCl₂ (s) ==> Ba²⁺(aq) + 2Cl^-(aq) ... dissolution of BaCl₂

q = mC∆T

q = heat = ?

m = mass = 20.8 g + 100 g = 120.8 g (your teacher may use 100 g and ignore the mass of the solute).

C = specific heat = 4.04 J/gº

∆T = change in temperature = 26.6 - 25.0 = 1.6º

q = (120.8 g)(4.184 J/gº)(1.6)

q = 809 J

The reaction "as written" shows 1 mole of BaCl2 dissolving. So, we will convert this answer to J/mole.

molar mass BaCl2 = 208 g/mol

20.8 g x 1 mol / 208 g = 0.100 moles

∆H_rxn = 809 J / 0.100 mols = 8090 J/mole