Introduction:Thermochemistry investigates the relationship between chemical reactions and energy changes involving heat. The amount of heat generated or absorbed in a chemical reaction can be studied using a calorimeter.
Purpose:The purpose of this laboratory was to determine the heat capacity of the calorimeter, and to understand thermodynamics/calorimetry by applying the calorimetry equation, Heat lost=Heat gained. We will use calorimetry to determine the heat involved when ammonium chloride, NH4Cl, dissolves in water. In this experiment our attention is focused on the reaction between ammonia and hydrogen chloride:
NH3 + HCl --> NH4Cl
Observation:When hot water was added to cold water, the temperature of the solution increased rapidly and then settled at approximately 45 degrees C. The cup felt quite warm when we touched it. Ammonium Chloride, NH4Cl, is a powder that does not have an odor to it. The temperature of the solution decreased when NH4Cl was added. The Ammonium Chloride finally dissolved in the water, and when we touched the cup it happened to be cold, in oppose to when we started the experiment.
Procedure:In CHM 1120, General Chemistry II Lab Manual, by Dr.Stanley-Pierre Ngeyi, pages 13-18.
Results Part A: Heat capacity of the calorimeter.
(b)^T=Tf-Ti(cold) = (45.0 degree C - 26.0 degree C) = 19 degrees C
( c)Heat lost by water is: qn=-nHCp,m(Tf-Ti(hot))
Mass if 50.0 mL of water:
Pwater = 1.00 g/mL
Pwater = Mass water / Volume water
Mass H2O = Pwater x Volume water = 1.00 g/mL x 50.0 mL = 50.0g H2O Moles H2O = 50.0 g / 18.02 g/mol = 2.77 moles H20
(d)Heat gained by cold water: qc = ncCp,m(Tf-Ti(cold))
(e)Heat gained by calorimeter: qcal = Ccal(Tf-Ti(cold))
(f)Heat lost = Heat gained
qH = qc + qcal...