To calculate the heat of mixing, we first need to determine the limiting reactant and the amount of heat released per mole of reaction. The balanced chemical equation for the reaction between HCl and NaOH is:HCl aq + NaOH aq NaCl aq + H2O l The reaction between HCl and NaOH is an exothermic neutralization reaction. The heat released during this reaction is known as the enthalpy of neutralization H_neutralization . For strong acids and strong bases, the enthalpy of neutralization is approximately -55.8 kJ/mol.First, let's determine the limiting reactant:Moles of HCl = volume in L concentration in mol/L = 20 mL 1 L/1000 mL 0.1 M = 0.002 molMoles of NaOH = 50 mL 1 L/1000 mL 0.2 M = 0.01 molSince there are fewer moles of HCl, it is the limiting reactant. The reaction will consume all 0.002 mol of HCl and produce 0.002 mol of NaCl and H2O.Now, we can calculate the heat of mixing using the enthalpy of neutralization:Heat of mixing q = moles of limiting reactant H_neutralizationq = 0.002 mol -55.8 kJ/mol = -0.1116 kJThe heat of mixing when 20 mL of a 0.1 M HCl solution is added to 50 mL of a 0.2 M NaOH solution at room temperature is -0.1116 kJ, assuming complete mixing and a constant pressure.