Calculator form
Use the responsive form below. It becomes three columns on large screens, two on smaller screens, and one on mobile.
Example data table
| Example | Mode | Key inputs | ΔT (°C) | qsolution (J) | qcal (J) | qreaction (J) | ΔH (kJ/mol) |
|---|---|---|---|---|---|---|---|
| Example 1 | Two-solution reaction | 50 mL + 50 mL, 1.00 g/mL, 1.00 M each, 24.5 °C and 24.7 °C, final 31.8 °C, Ccal 35 | 7.20 | 3012.48 | 252.00 | -3264.48 | -65.29 |
| Example 2 | Single-solution experiment | 125 g, c = 4.18, initial 23.5 °C, final 27.0 °C, Ccal 28, reacted moles 0.040 | 3.50 | 1828.75 | 98.00 | -1926.75 | -48.17 |
Formula used
1) Mass from volume and density: m = V × ρ
2) Weighted initial mixture temperature for two-solution mode: Tinitial,mix = (mATA + mBTB) / (mA + mB)
3) Temperature change: ΔT = Tfinal - Tinitial
4) Heat gained by solution: qsolution = m × c × ΔT
5) Heat gained by calorimeter: qcal = Ccal × ΔT
6) Heat of surroundings: qsurroundings = qsolution + qcal
7) Heat of reaction: qreaction = -qsurroundings
8) Reaction extent in two-solution mode: extent = min(nA/νA, nB/νB)
9) Molar enthalpy: ΔH = qreaction / extent or ΔH = qreaction / n, then convert joules to kilojoules per mole.
A positive qreaction indicates an endothermic process. A negative qreaction indicates an exothermic process.
How to use this calculator
- Select the experiment mode that matches your lab setup.
- Enter a trial name so exported files stay organized.
- For two-solution work, enter both volumes, densities, molarities, stoichiometric coefficients, and initial temperatures.
- For single-solution work, enter total mass, initial temperature, final temperature, and reacted moles if known.
- Use an appropriate specific heat capacity. Water-like solutions commonly use 4.184 J g-1 °C-1.
- Add the calorimeter constant if your cup and thermometer absorb measurable heat.
- Press the calculate button. The result will appear above the form under the header section.
- Use the CSV and PDF buttons to save calculations, then inspect the Plotly graph for the energy balance view.
FAQs
1. What does coffee cup calorimetry measure?
It measures heat transferred at constant pressure in a simple insulated cup setup. You can estimate reaction heat, solution heat gain, calorimeter heat gain, and molar enthalpy from temperature data.
2. Why is the reaction heat the negative of surrounding heat?
The solution and calorimeter are treated as surroundings. If they gain heat, the reaction lost that same amount. The sign flips because energy released by one part is absorbed by the other.
3. When should I include a calorimeter constant?
Include it whenever the cup, lid, stirrer, or thermometer noticeably absorbs heat. Leaving it out can underestimate the magnitude of reaction heat, especially for precise laboratory work.
4. What if the two starting solutions have different temperatures?
This calculator handles that by estimating a weighted initial mixture temperature from both solution masses and their starting temperatures. That improves accuracy compared with simply averaging the temperatures.
5. Why is ΔH sometimes not shown?
ΔH requires a positive reacted amount. In two-solution mode, that comes from concentrations and stoichiometric coefficients. In single-solution mode, it comes from reacted moles entered directly.
6. Can I use this for neutralization, dissolution, or dilution experiments?
Yes. It works for many constant-pressure calorimetry experiments as long as your mass, temperature, heat capacity, and reacted amount assumptions are reasonable for the system.
7. Should density always be set to 1.00 g/mL?
No. That value is a useful approximation for dilute aqueous solutions, but concentrated or nonaqueous mixtures can differ. Enter measured densities whenever better accuracy matters.
8. What improves the reliability of calorimetry results?
Use fast mixing, calibrated temperature probes, consistent timing, measured densities, a known calorimeter constant, and minimal heat loss to the room. Replicate trials also help reveal random error.