Question

In a constant-pressure calorimeter, 70.0 mL of 0.340 M Ba(OH)2 was added to 70.0 mL of 0.680 M HCl. The reaction caused the temperature of the solution to rise from 21.03 °C to 25.66 °C. If the solution has the same density and specific heat as water (1.00 g/mL and 4.184 J/g·K, 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

The reaction taking place follows the next stoichiometric relation:

Ba(OH)₂ + 2HCl -> 2H₂O + BaCl₂

The heat generated by the reaction will be expressed as the following thermodynamic expression:

Q = mCpdeltaT

mass = 140 mL * (1g/mL) = 140 grams

Cp = 4.184 J / g K

deltaT = (25.66 - 21.03) = 4.63 ºC

Q = 140 g * (4.184 J / g K) * (4.63 K) = 2712.069 J

We now have the heat generated, which has to be divided by the number of moles of water produced in the process, which will be obtained as follows:

0.0476 moles of HCl are used, which are equivalent to th 0.0476 moles of water produced.

So, heat of reaction will be:

deltaH_rxn= 2712.069 J / 0.0476 moles of H2O = 56976.24 J / mol of H₂O = 56.98 kJ / mol of H₂O