Heat of Solution Calculator

Calculate enthalpy of solution using calorimetry data: q = mc*delta T, then delta H = -q/n. Determine if dissolution is endothermic or exothermic from temperature change.

⚗️ Thermochemistry📐 ΔH°soln = -q/n🧪 Chemistry
Mass of solution m (g)
Specific heat c (J/g·°C)
Temperature change ΔT (°C)
Moles of solute n
Please enter valid values.

Formula & Reference

VariableSymbolFormulaUnits
Heat of Solution CalculatorSee formulaΔH°soln = -q/nkJ/mol

Step-by-Step Examples

Example 1
NaOH Dissolving

0.050 mol NaOH in 200 g water. Temperature rises 5.00 C. c=4.184.

  • q(soln) = 200x4.184x5.00 = 4184 J (water warms)
  • q(rxn) = -4184 J (exothermic)
  • dH = -4184/(0.050x1000) = -83.7 kJ/mol
✓ dH(soln, NaOH) = -83.7 kJ/mol (exothermic)
Example 2
NH4NO3 Dissolving

0.040 mol NH4NO3 in 150 g water. Temperature drops 4.00 C.

  • q(soln) = 150x4.184x(-4.00) = -2510 J (water cools)
  • q(rxn) = +2510 J (endothermic)
  • dH = +2510/(0.040x1000) = +62.8 kJ/mol
✓ dH(soln, NH4NO3) = +62.8 kJ/mol (endothermic, used in cold packs)
Example 3
NaCl Dissolving

0.100 mol NaCl in 180 g water. Temperature changes +0.32 C.

  • q(soln) = 180x4.184x0.32 = 241 J
  • q(rxn) = -241 J
  • dH = -241/(0.100x1000) = -2.41 kJ/mol (approx.)
✓ dH(soln, NaCl) ~ -2.4 kJ/mol (nearly zero)

Real-World Applications

🧊
Cold Packs
NH4NO3 and urea dissolve endothermically, absorbing heat from surroundings.
🥵
Hot Packs
CaCl2 and NaOH dissolve exothermically, releasing heat. Used in hand warmers.
💊
Drug Solubility
Dissolution enthalpy affects how solubility changes with temperature.
🧪
Lab Safety
Highly exothermic dissolution (e.g., conc H2SO4 in water) requires slow addition and cooling.

Common Mistakes to Avoid

⚠️
Sign convention for temperature change

If T rises: dT positive, q(solution) positive, q(rxn) = -q(solution) < 0 (exothermic). If T drops: dT negative, q(rxn) > 0 (endothermic).

⚠️
Use total solution mass

Use mass of water + mass of dissolved solute, not just water. For dilute solutions, solute mass is often small enough to ignore.

⚠️
Convert J to kJ for dH

q is in joules; dH is in kJ/mol. Divide by (n x 1000).

Frequently Asked Questions

What determines if dissolution is exo or endo? ▾
Balance of lattice energy (endothermic, breaking crystal) vs solvation enthalpy (exothermic, ion-water attraction). If solvation > lattice energy: exothermic.
Why does NaCl dissolve even though slightly endothermic? ▾
Entropy drives it. dG = dH - TdS. Positive dS (mixing) makes dG < 0 even for slightly positive dH.
What are heats of solution for common salts? ▾
NaCl: +3.9 kJ/mol. NaOH: -44.5 kJ/mol. NH4NO3: +25.7 kJ/mol. CaCl2: -82.8 kJ/mol. H2SO4: -96.2 kJ/mol.
Why is H2SO4 so dangerous to mix with water? ▾
Dissolution of H2SO4 is highly exothermic (-96 kJ/mol). Adding water to acid can cause violent boiling; always add acid to water slowly.
What is integral vs differential heat of solution? ▾
Integral: heat for dissolving in finite amount of solvent. Differential: heat at infinite dilution. They differ in concentrated solutions due to ion-ion interactions.

Related Chemistry Calculators

🌡️ Calorimetry🌡️ Specific Heat🔥 Enthalpy🧪 Lattice Energy🧪 Molarity

Formula Explorer connections

Interpretation: This relationship tracks energy transfer, state-function change or the balance between enthalpy and entropy in a chemical process. Assumption: Keep energy units compatible, use kelvin for absolute temperature, and match standard states and reaction stoichiometry. Thermodynamic favorability does not determine reaction speed.

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