To calculate the standard enthalpy change for the reaction, we first need to determine the amount of heat released or absorbed during the reaction. We can do this using the formula:q = mcTwhere q is the heat released or absorbed, m is the mass of the solution, c is the specific heat capacity, and T is the temperature change. However, since the temperature change is negligible, we need to find another way to calculate the heat released or absorbed.We can do this by first determining the limiting reactant in the reaction. The balanced chemical equation for the reaction between HCl and NaOH is:HCl aq + NaOH aq NaCl aq + H2O l The moles of HCl and NaOH can be calculated as follows:moles of HCl = volume concentration = 50.0 mL 0.20 M = 10.0 mmolmoles of NaOH = volume concentration = 50.0 mL 0.10 M = 5.0 mmolSince there are fewer moles of NaOH, it is the limiting reactant. The reaction will proceed until all the NaOH is consumed. The moles of HCl and NaOH that react are equal to the moles of the limiting reactant:moles of HCl that react = 5.0 mmolmoles of NaOH that react = 5.0 mmolNow we can calculate the heat released or absorbed using the enthalpy of the reaction. The enthalpy of the reaction can be determined using a known value for the enthalpy of neutralization, which is the enthalpy change when an acid and a base react to form water. For strong acids and bases, like HCl and NaOH, the enthalpy of neutralization is approximately -57.3 kJ/mol.Enthalpy change for the reaction = moles of limiting reactant enthalpy of neutralizationH = 5.0 mmol -57.3 kJ/mol = -286.5 kJ/molSince the enthalpy change is negative, the reaction is exothermic, meaning that heat is released during the reaction. The standard enthalpy change for the reaction between 50.0 mL 0.20 M HCl aq and 50.0 mL 0.10 M NaOH aq in a constant pressure calorimeter is -286.5 kJ/mol.