Thakgatso Faith Phukane 4336600
Heat of Neutralisation 17 October 20224
Introduction:
Thermodynamics is the study of the relationship between heat (or energy) and work.
Enthalpy is a central factor in thermodynamics. It is the heat content of a system. The heat
that passes into or out of the system during a reaction is the enthalpy change. Whether the
enthalpy of the system increases (i.e. when energy is added) or decreases (because energy is
given off) is a crucial factor that determines whether a reaction can happen.
The heat of neutralization (ΔHn) is the change in enthalpy that occurs when one equivalent of
an acid and one equivalent of a base undergo a neutralization reaction to form water and a
salt. When a reaction is carried out under standard conditions at the temperature of 298 K (25
degrees Celsius) and 1 atm of pressure and one mole of water is formed it is called the
standard enthalpy of neutralization (ΔHn o). Enthalpy of neutralization is always constant for
a strong acid and a strong base: this is because all strong acids and strong bases are
completely ionized in dilute solution. Enthalpy changes in neutralization are always negative-
when an acid and alkali react, heat is given out.
When a powerful acid and a powerful base react, enthalpy change is unique. It may be clearer
in the example: NaOH (aq) + HCl (aq) --- NaCl (aq) + H 2O (l). When we consider this
reaction, it is clear the only reaction we can see inside this is: H + (aq) + OH- (aq) ----H2O (l).
Enthalpy change of this reaction is -57 kJ mol−1 When a weak acid reacts with a powerful
base the enthalpy change must be a less enthalpy change than -57 kJ mol−1, weak acids in
solution do not fully dissociate to their respective anions and cations. To dissociate these
bonds some amount of energy is needed; the enthalpy change reduces. In this experiment the
reaction is exothermic, an exothermic reaction occurs when more energy is released by the
formation of new bonds than is consumed by breaking old bonds.
Aim:
In this experiment, the molar enthalpy of neutralization will by determined using NaOH and
HCL.
Methodology
Two 250ml beakers were collected from drawers and cleaned up. 50ml of HCl solution was
placed into beaker and 55ml of NaOH solution was placed into the second beaker. The
temperature of each solution was measured and recorded. After mixing the two solutions in
the white plastic solution cups and stirred, the temperature of the mixed solution was
measured and recorded. The solution was then discarded into the waste bottle and working
area was cleaned up.
Results and discussion:
Volume of solution Measured Concentration
added temperature
HCl 50ml 21ºC 1,20M
NaOH 55ml 21 ºC 1,30M
Temperature of the mixed solutions of HCL and NaOH: 24 ºC
Calculations
Calculating the number of moles: n(HCl)=CV= 1,20 *0,050 = 0,060moles
N(NaOH)=CV= 1,30*0,055= 0,0715moles
Hence HCL is the limiting reagent.
Given:
heat capacity: 3,97J/g
density: 1,02g/ml
Ccal: 42,0 J/ºC
ΔT= 24-21= 3 ºC
Questions:
1. Weight = density * total volume = 1,02g/ml *105,0 ml= 107,1g
2. Q=mC×ΔT
= 107,1Gg* 3,97J/g * 3 ºC= 1275,561 J
3. Q=C×ΔT
Q= 42,0 J/ ºC * 3 ºC=126 J
4. Total number of joules: 1275,561 + 126= 1401.561 J
5. Molar heat of neutralization= q/n
n(HCl)= C*V= 1,20 mol/L * 50L =60 moles
q= 1401,561J
molar heat of neutralisation= q/n = 1401,561/ 60
= 23,36 J/mol.
6. The reaction is liberated
7. In manufacturing, neutralization reactions are used to treat acidic waste products.
Understanding the heat generated helps manage the temperature of chemical
processes, ensuring safety and efficiency.
Conclusion:
The reaction in this experiment is exothermic because the heat is liberated not gained. The
temperature of the two solutions remained constant and the temperature changed towards
mixing the solutions together.
List of references
Papee, H.M., Canady, W.J., and Laider, K.J., 1956 “The Heat of Neutralization of strong
acids and bases I highly dilute aqueous solutions” Canadian Journal of Chemistry, vol.34,
pp. 1678-1683. [ Online]. Available at: https://doi.org/10.1139/v56-216 (Accessed: December
1956)
Mendham, J., Denny, R.C., and Thomas, M.J., 2000, “Choice of indicators in Neutralization
Reactions” Vogel’s Textbook of Quantitative Chemical Analysis 6 th edition, p. 351, Published
by: Pearson Education Limited
Daniel, C.H., 2007 “Enthalpy of Neutralization, Quantitative Chemistry Analysis Freeman
and Company” Community of College of Rhode Island, Retrieved from Wikipedia on 24
February 2014. (Accessed: 3 July 2017)
Wendell, J., and Weber, N., 1954, “Heat of Neutralisation at high acid-base concentrations”
Contribution from the department of chemistry, pp. 4290-4295. [Online] (Accessed: 29
March 1954)
Sawyer, J. 2016, “The effect of Neutralisation on Heat Change and Entropy” South Carolina
JuniorAcademyofscience,p.204.
Availableat:https://scholarexchange.furman.edu/scjas/2016/all/204
