The document discusses heat of precipitation, which is the energy change that occurs when one mole of precipitate is formed from its ions in a precipitation reaction. As an example, it states that the precipitation reaction of lead nitrate and sodium sulfate forming lead sulfate and sodium nitrate releases -50.4 kJ of energy per mole of lead sulfate formed. It also provides methods for calculating the heat released when different amounts of lead sulfate are formed using the heat of precipitation value.

1. Heat of Precipitation
 Definition:
 Energy change when one mole of precipitate is formed
from its ions.
 Example:
Precipitation reaction
Pb(NO3)2 + Na2SO4  PbSO4 + 2NaNO3
∆H = -50.4 kJ mol-1
Ionic equation
Pb2+ + SO42-  PbSO4
50.4 kJ heat energy is released during
the formation of 1 mole of lead
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2. Heat of Precipitation
Pb(NO3)2 + Na2SO4  PbSO4 + 2NaNO3 ∆H = -50.4 kJ mol-1
∆H means……..
 50.4 kJ of heat energy is released when 1 mole of
PbSO4 if formed.
50.4 kJ of heat released when 1 mole of PbSO4 is formed
?? J of heat released when 0.2 moles of PbSO4 is formed
5040 J of heat released when ?? mole of PbSO4 is formed
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3. How to Determine Heat of Precipitation
Number of moles = mv
1000
m = mass of the aqueous reaction
mixture
c = specific heat capacity of the aqueous
reaction mixture
Θ = change in temperature
Assumption:
• Density of the aqueous reaction
mixture is 1 g cm-3
• Specific heat capacity of the aqueous
reaction mixture is 4.2 Jg-1 OC-1
• No heat is lost to the surrounding
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