Answer:
3.00 J/mmol
Explanation:
The temperature of the solution is increasing, so it's an endothermic reaction. The heat that is being absorbed can be calculated by:
Q = m*c*ΔT
Where m is the total mass (HCl + NaOH), c is the specific heat, and ΔT is the variation of the temperature (final - initial). Because the molarity is small, the solutions are basically water, so c = 4.184 J/g°C.
The mass is the molar mass multiplied by the number of moles (n), which is the volume multiplied by the molarity:
nHCl = 0.9 mol/L *0.019 = 0.0171 mol
nNaOH = 0.9 mol/L *0.019 = 0.0171 mol
Molar masses: HCl = 36.5 g/mol; NaOH = 40 g/mol
mHCl = 36.5*0.0171 = 0.62415 g
mNaOH = 40 * 0.0171 = 0.6840 g
m = 1.30815 g
Q = 1.30815*4.184*(37.8 - 28.8)
Q = 49.2597 J
Because the number of moles of NaOH is equal to the number of moles of HCl, and the stoichiometry of the neutralization is 1:1, they both react completely, so the enthalpy can be calculated based in any of them. The enthalpy is the heat divided by the number of moles. In mmol, n is 17.1 mmol.
ΔH = 49.2597/17.1
ΔH = 2.88 J/mmol
ΔH = 3.00 J/mmol
