To calculate the standard enthalpy change for the reaction, we first need to determine the 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 change in temperature.First, we need to find the mass of the solution. Since the density of water is approximately 1 g/mL, the mass of the 100 mL solution 50 mL HCl + 50 mL NaOH is approximately 100 g.Next, we can calculate the change in temperature T as follows:T = T_final - T_initial = 31.2C - 25C = 6.2CNow we can calculate the heat released or absorbed q using the formula:q = mcT = 100 g 4.184 J/gC 6.2C = 2594.08 JSince the temperature of the solution increased, the reaction is exothermic, and the heat released q is negative:q = -2594.08 JNow we need to determine the moles of the limiting reactant. Both HCl and NaOH have a concentration of 1.0 M and a volume of 50 mL, so they react in a 1:1 ratio. Therefore, the limiting reactant is either one, and we can calculate the moles as follows:moles = 1.0 mol/L 0.050 L = 0.050 molFinally, we can calculate the standard enthalpy change H by dividing the heat released q by the moles of the limiting reactant:H = q / moles = -2594.08 J / 0.050 mol = -51881.6 J/molThe standard enthalpy change for the reaction between 50 mL of 1.0 M HCl and 50 mL of 1.0 M NaOH at 25C is approximately -51.9 kJ/mol.