Question

In a constant-pressure calorimeter, 70.0 mL of 0.300 M Ba(OH)2 was added to 70.0 mL of 0.600 M HCl. The reaction caused the temperature of the solution to rise from 21.98 °C to 26.07 °C. If the solution has the same density and specific heat as water (1.00 g/mL and 4.184 J/g·°C, respectively), what is ΔH for this reaction (per mole of H2O produced)? Assume that the total volume is the sum of the individual volumes.

Answer 1

moles of acid HCl = 70 x 0.60 / 1000 = 0.042

moles of Ba(OH)2 = 70 x 0.3 / 1000 = 0.021

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

1                2

0.021     0.042

here both are consumed

moles of water fomred = 0.042

total volume = 70.0+ 70.07 = 140 mL

mass of solution = volume x density

                          = 140 x 1

                         = 140 g

dT = 26.07 -21.98 = 4.09 oC

Q = m Cp dT

Q = 140x 4.184 x 4.09

Q = 2396 J

molar enthalpy of neutralization = - Q / n

                                                    = -2.396 / 0.042

                                        = - 57.0 kJ / mol

ΔH = - 57.0 kJ / mol