Question

Calculate the heat of mixing (in kJ/mol) when 100 mL of 0.2 M HCl is added to 200 mL of 0.1 M NaOH at 25°C. Assume the density of the resulting solution is 1 g/mL and specific heat capacity is 4.18 J/(g*K). Also, assume the heat capacity of the solution is the same as water.

Answer 1

To calculate the heat of mixing, we first need to determine the amount of heat released during the neutralization reaction between HCl and NaOH. The balanced chemical equation for this reaction is:HCl  aq  + NaOH  aq   NaCl  aq  + H2O  l The heat released during this reaction can be calculated using the enthalpy of neutralization, which is the heat released when one mole of water is formed from the reaction between an acid and a base. The enthalpy of neutralization for a strong acid and a strong base, like HCl and NaOH, is approximately -57.1 kJ/mol.Next, we need to determine the number of moles of HCl and NaOH in the solution. Moles of HCl =  volume in L    concentration in mol/L Moles of HCl =  0.1 L    0.2 mol/L  = 0.02 molMoles of NaOH =  volume in L    concentration in mol/L Moles of NaOH =  0.2 L    0.1 mol/L  = 0.02 molSince the moles of HCl and NaOH are equal, the reaction goes to completion, and all of the HCl and NaOH will react to form NaCl and water.Now, we can calculate the heat released during the reaction:Heat released =  moles of HCl    enthalpy of neutralization Heat released =  0.02 mol    -57.1 kJ/mol  = -1.142 kJThe heat of mixing is the heat released during the reaction, which is -1.142 kJ. Since the heat is released, it is exothermic, and the negative sign indicates that the heat is being released to the surroundings.