Designing a Hand Warmer
http://group.chem.iastate.edu/Greenbowe/sectio
ns/projectfolder/flashfiles/thermochem/solutionS
alt.html
Breaking bonds and particulate attractions
absorb E from the surroundings, while forming
new bonds and particulate attractions release
energy to the surroundings. When an ionic solid
dissolves in water, ionic bonds between + and –
ions and H bond b/t water molecules are broken,
and NEW attractions between water/anions and
cations are formed. The E required to break
these bonds and form new ones depends on the
properties of the anions and cations.
Heat evolved, q = -, exothermic
Heat absorbed, q = + and endothermic
ENTROPY of solution is ALWAYS (+)
Pre-Lab
Part A:
• Heat Capacity of the Calorimeter
Part B:
• Practice Calorimetry Procedure
with MgSO4(s)
Information in Data Tables
Heat Capacity of Calorimeter
Magnesium Sulfate
Volume deionized water (cold)
Volume of water
Temp. of Cold
Mass of MgSO4
Volume of deionized water (hot)
T initial
Final temperature
T final
DT cold
DT
DT hot
q cold (J)
q hot (J)
DT cal
Calorimeter Constant (J/oC)
In groups, review the calorimetry procedure
and answer the following questions:
Each group will use 3 solids (we will share
data at the end)
Group A:
• ammonium nitrate
• Calcium chloride
• Sodium acetate
Group B:
• Sodium chloride
• Lithium chloride
• Sodium carbonate
Calculations Table
Solid
NaC2H3O2
CaCl2
Na2CO3
NaCl
LiCl
NH4NO3
DT (oC)
q rxn
q cal
q soln
Molar mass Moles used Enthalp of
dissolution
DH soln
(kJ/mol)