Question

A dilute solution of hydrochloric acid with a mass of 607.23 g and containing 0.33131 mol of HCl was exactly neutralized in a calorimeter by the sodium hydroxide in 614.70 g of a comparably dilute solution. The temperature increased from 15.848 to 19.739 °C. The specific heat of the HCl solution was 4.031 J·g^-1·°C^-1; that of the NaOH solution was 4.046 J·g^-1·°C^-1. The heat capacity of the calorimeter was 77.99 J·°C^-1.

Enter the balanced equation for the reaction. Include states in your answer.

Use the data above to calculate the heat evolved. What is the heat of neutralization per mole of HCl? Assume that the original solutions made independent contributions to the total heat capacity of the system following their mixing.
ΔH = ___ kJ/mol

Answer 1

(i) Enter the balanced equation for the reaction. Include states in your answer.
ANSWER:
NaOH(aq) + HCl(aq) = NaCl(aq) + H2O(l)

(ii) Use the data above to calculate the heat evolved.
ANSWER:
Mass of HCl solution, Wa = 607.23g
Specific heat of the HCl solution, Cpa = 4.031 J·g-1·°C-1

Mass of NaOH solution, Wb = 614.70g
Specific heat of the NaOH solution, Cpb = 4.046 J·g-1·°C-1

Temperature change, DT = 19.739-15.848=3.891 C
Heat capacity of the calorimeter, Cpc = 77.99 J·°C-1

Heat evolved, Q = Heat taken by HCl solution + Heat taken by NaOH solution + Heat taken by calorimeter
A = DT*Wa*Cpa + DT*Wb*Cpb + DT*Cpc = DT*(Wa*Cpa + Wb*Cpb + Cpc)
Q = 3.891*(607.23*4.031 + 614.70*4.046 +77.99) = 19505 J = 19.505 kJ

(iii) What is the heat of neutralization per mole of HCl?
Assume that the original solutions made independent contributions to the total heat capacity of the system following their mixing.

ANSWER:
Moles of HCl neutralized, n = 0.33131
Heat evolved, Q = 19.505 kJ

ΔH = -Q/n = -19.505/0.33131 = -58.9 kJ/mol
Negative sign as heat is being evolved.