Some hydrated ionic solids when heated release their water of crystallisation and dissolve in this water. When the solution is cooled the solid recrystalizes and heat is released. One example is calcium chloride hexahydrate and the process is described by the equation
CaCl2.6H2O => CaCl2.2H2O + 4H2O delta H = +37.2kJ
Process is reversible.
Draw the energy level diagram for the above(forward) reaction
It is the exothermic reaction yea? The forward reaction I mean. Because according to the passage, heat is released only when the solid recrystalizes. In the forward reaction, crystals are being formed?
By the way which of the formula exist as the powder and which one exists as the crystals? CaCl2.6H2O and CaCl2.2H2O ?
2
Calculate the energy absorbed when 100kg of calcium chlroide hexahydrate undergoes the above reaction. Leave answer to nearest kJ.
So to find the mass of CaCl2.6H2O, I have to get the Mr. Is that is being calculated include the 6H2O? Referring to value of 6..thanks
Originally posted by bonkysleuth:Some hydrated ionic solids when heated release their water of crystallisation and dissolve in this water. When the solution is cooled the solid recrystalizes and heat is released. One example is calcium chloride hexahydrate and the process is described by the equation
CaCl2.6H2O => CaCl2.2H2O + 4H2O delta H = +37.2kJ
Process is reversible.
Draw the energy level diagram for the above(forward) reaction
It is the exothermic reaction yea? The forward reaction I mean. Because according to the passage, heat is released only when the solid recrystalizes. In the forward reaction, crystals are being formed?
By the way which of the formula exist as the powder and which one exists as the crystals? CaCl2.6H2O and CaCl2.2H2O ?
2
Calculate the energy absorbed when 100kg of calcium chlroide hexahydrate undergoes the above reaction. Leave answer to nearest kJ.
So to find the mass of CaCl2.6H2O, I have to get the Mr. Is that is being calculated include the 6H2O? Referring to value of 6..thanks
The heating of the hexahydrate form is of course endothermic (hence "heating of"). The formation of the hexahydrate form is exothermic, due to the interactions* between the water and the ions.
The crystalline form refers to the hexahydrate.
Yes, the 100kg refers to the hexahydrate and hence the molar mass includes the 6 water molecules per formula unit of the ionic compound.
*Interestingly, not all of the "water of crystallization" has direct ion-dipole or dative coordinate bonds with the ions. It's somewhat more complex than what many students may think :