Heat Lost or Gained by the Solution, q_soln
Use the calorimetry equation to calculate q_soln. Your values here are all measured for the solution, which is the "surroundings" for the reaction. Assume that the specific heat of the solution is the same as the specific heat of water (4.184 J/(g°C)).
q_solution = (m_solution × S_solution × ΔT_solution)
Heat Lost or Gained by the Solution, q_soln: q
q
Heat Lost or Gained by the dissolving salt, q_salt
In this experiment, we are considering the system to be the reaction itself and the calorimeter and resulting solution to be the surroundings. Assume that all the heat generated by the reaction (the system) is transferred to the solution (the surroundings). Therefore, the heat generated or absorbed by dissolving the salt is simply the negative of the heat absorbed by or removed from the solution.
q_salt = -q_soln
Heat Lost or Gained by the dissolving salt, q_salt: q
Moles of salt
Use the molar mass of the salt to convert the mass of the salt to moles.
Moles of salt: â—»
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ΔH_solv
The molar enthalpy of solvation is based on the heat lost or gained per mole of material dissolved and is generally reported in kJ/mol. Use the equation below to calculate the ΔH_solv for each salt. Since your measured q values are in joules, you will need to convert to kilojoules. The enthalpy, ΔH_solv, will be negative for an exothermic reaction and positive for an endothermic reaction.
ΔH_solv = (q_salt) / (moles salt)
ΔH_solv: q
Part 3. Determining the Heat of Reaction
Mass of Acid solution, m_a
The acid solution is dilute, so the density is approximately that of water. You can use 1.00 g/mL to convert the volume of acid to mass. (Note that this is the mass of HCl and water together.)
Mass of acid solution, m_a: q
Total Mass of Reaction Solution, m_sol
The total mass of the solution is the combined mass of the aqueous acid solution and the magnesium.
Mass of Reaction Solution, m_soln: q
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