The balanced chemical equation for the neutralization of HCl with
is:

Given weight of
= 5g
Moles of
= 
Volume of HCl solution = 
Assuming the density of the solution is 1.0 g/mL
Mass of HCl solution = 50 g
Overall mass of the solution = 50 g + 5 g = 55 g
To find the heat of neutralization, we calculate:
Q = m C ΔT
where m equals the mass of the solution = 55 g
C represents the specific heat capacity of the solution = 4.184
ΔT signifies the temperature change = 6.8 K = (6.8 - 273) C = -266.2

The enthalpy of neutralization per mole of 
= 