Molar Heat of Solution Calculator
Calculate the molar heat (enthalpy) of solution from a calorimetry temperature change and moles of solute.
How it works
q = m · c · ΔT · ΔH_soln = −q / n
In a coffee-cup calorimeter the heat released or absorbed by dissolving a solute shows up as a temperature change in the solution. That heat is q = m·c·ΔT. Dividing by the moles of solute and flipping the sign (heat gained by the solution is heat lost by the dissolving process) gives the molar enthalpy of solution: negative for exothermic dissolving, positive for endothermic.
Worked example
Dissolving 0.05 mol of solute warms 100 g of solution by 5 °C: q = 100 × 4.18 × 5 = 2,090 J. ΔH_soln = −2,090 / 0.05 = −41,800 J/mol = −41.8 kJ/mol (exothermic).
Frequently asked questions
Why is the sign flipped?
The temperature rise measures heat gained by the solution, which equals the heat released by the dissolving process. By convention an exothermic reaction has a negative ΔH, so q is negated.
What mass should I use?
Use the total mass of the resulting solution (solvent plus dissolved solute), since that is what changes temperature in the calorimeter.
Why assume the specific heat of water?
Dilute aqueous solutions behave close to pure water (about 4.18 J/g·°C). For concentrated or non-aqueous solutions, use the measured specific heat instead.
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