Molar Enthalpy of Salt: Calculation and Heat Sources

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SUMMARY

The discussion focuses on the calculation of molar enthalpy for three salts: ammonium chloride (NH4Cl), potassium nitrate (KNO3), and lithium chloride (LiCl). The participants clarify that the correct approach involves using the mass of both the water and the salt when calculating heat using the equation mcΔt. They emphasize the distinction between "heat of dissolution" and "enthalpy of dissolution," noting that specific heat capacity should ideally reflect the solution rather than just pure water, although using water's specific heat is generally acceptable for diluted solutions.

PREREQUISITES
  • Understanding of thermodynamic concepts, specifically enthalpy and heat transfer.
  • Familiarity with the equation mcΔt for calculating heat transfer.
  • Knowledge of specific heat capacity and its application in solutions.
  • Basic laboratory skills for conducting experiments with salts and measuring heat changes.
NEXT STEPS
  • Research the specific heat capacity of various salt solutions.
  • Learn about the differences between heat of dissolution and enthalpy of dissolution.
  • Explore advanced calorimetry techniques for accurate heat measurements.
  • Study the impact of concentration on the thermodynamic properties of solutions.
USEFUL FOR

Chemistry students, laboratory technicians, and researchers involved in thermodynamics and solution chemistry will benefit from this discussion.

Hannah Wallace
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Please post this type of questions in HW section using the template.
So for a lab I had to test three different salt Nh4Cl,KN03 and LiCl. I found the heat of each of them and then in turn found the molar enthalpy by using N*molar enthalpy=-heat. When finding my heat and using equation mcΔt would I use the mass of the water or the mass of the water and the salt?
 
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Note: things like "heat", "enthalpy" are properties of a process, not of a substance, so what you wrote doesn't make much sense. I guess what you mean is "heat of dissolution" and "enthalpy of dissolution" (AKA "heat/enthalpy of solution").

Mass of water and salt is a bit more correct, although technically you should also use specific heat capacity of the solution, not of the pure water. For diluted solutions using specific heat capacity of water is usually accurate enough.
 

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