Calorimetry

Topics: Thermodynamics, Measurement, Chemistry Pages: 2 (466 words) Published: June 17, 2013
Experiment: Calorimetry
Laboratory Experiment – Heat of Solution
Aim:
The aim was to use calorimetric measurements to calculate the molar heat of solution of NaOH and NH4NO3. Method:
1. 50g of water was poured into a clean polystyrene calorimeter (Styrofoam cup) and the initial temperature was measured. 2. A teaspoon of 2g of the selected salt was measured and added into the water. 3. The solution was stirred and the final temperature was measured when the solution stabilised and the results were recorded. 4. Repeat experiment with the other salt.

Note: Calorimetry is the technique used to measure the heat changes during a chemical reaction. Results:
(assume density of water is 1ml = 1g)
| Sodium Hydroxide| Ammonium Nitrate|
Mass of Solute (g)| 2| 2|
Volume of Water (ml)| 50| 50|
Initial Temperature (oC)| 25| 25|
Final Temperature (oC)| 34.4| 22.2|

NaOH calculation| NH4NO3 calculation|
Q = mCΔT
= 52 x 4.18 x (34.4 - 25)
= 2043.184 J
n = m/M = 2/23 + 16 + 1
= 0.05 mol
ΔHs = -Q/n
= -2043.184 / 0.05
= -40863.68 J/mol = -40.86 kJ/molΔHS NaOH = -40.86 kJ < 0 ∴ exothermic reaction| Q = mCΔT
= 52 x 4.18 x (22.2 - 25)
= -608.608 J
n = m/M = 2/(14 + 4 x 1) + (14+16 x 3)
= 0.025ΔHs = -Q/n
= 608.608 / 0.025
= 24344.32 J/mol = 24.34 kJ/molΔHS NH4NO3 = 24.34 > 0 ∴ endothermic reaction|

Discussion
The dissolution of NaOH is an exothermic process whereas the dissolution of NH4NO3 is an endothermic process. Sources of Error
* Main source of error is in the exothermic process is heat lost to the surroundings through the lid and container, compromising validity of results. * In an endothermic process the heat absorbed by the dissolution process may come from sources other than the water (e.g. lid, container) * Measurement errors e.g. mass of solute, volume of water, temperature of water * There may have been an accumulation of heat where...
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