Question

Assume 200. mL of 0.400 M HCl is mixed with 200 mL of 0.250 M Ba(OH)2 in a constant-pressure calorimeter. The temperature of the solutions before mixing was 25.10C; after mixng and alowing the reaction to occur, the temperature is 27.78C. Determine  ΔrH for this reaction in units of kJ/mol-rxn.

2 HCl(aq) + Ba(OH)2(aq) -> BaCl2(aq) + 2 H2O(l)

The densities of all solutions are 1.00 g/mL
The specific heat capacitites of all solutions are 4.20 J/(gC)

Answer 1

Assume 200. mL of 0.400 M HCl is mixed with 200 mL of 0.250 M Ba(OH)2 in a constant-pressure calorimeter. The temperature of the solutions before mixing was 25.10C; after mixng and alowing the reaction to occur, the temperature is 27.78C. Determine  ΔrH for this reaction in units of kJ/mol-rxn.

2 HCl(aq) + Ba(OH)2(aq) -> BaCl2(aq) + 2 H2O(l)

The densities of all solutions are 1.00 g/mL
The specific heat capacitites of all solutions are 4.20 J/(gC)

Ba(OH)₂ + 2HCl → BaCl₂ + 2H₂O
1 mole of Ba(OH)₂ reacts with 2 moles of HCl to give 2 moles of H₂O

Initial number of moles of Ba(OH)₂ = 0.250 × (200/1000) = 0.05 mol

Initial number of moles of HCl = 0.400 × (400/1000) = 0.16 mol

When all Ba(OH)₂, no. of moles of HCl needed = = 0.16 mol

Both the reactants completely react.
Number of moles of water formed = 0.16 × 1 = 0.16 mol

Heat released = m c ΔT = (200 + 200) × 4.184 × (27.78 - 25.10) = 4485.248 J= 4.485248kJ

ΔH = -4485.248 /0.16 = 28.032 kJ/mol of H₂O produced