enthalpy change calculator - Aaron Graves, PhDude Replica

Interactive Enthalpy Change Calculator

Use this tool to calculate heat transfer (q) and, if needed, molar enthalpy change (ΔH) from calorimetry data.

Heat of sample/surroundings: q = m × c × ΔT

Reaction enthalpy from calorimetry: ΔH_rxn = -q / n

Calculation Mode

Mass, m (g)

Specific Heat Capacity, c (J/g°C)

Tip: For liquid water, use 4.184 J/g°C.

Initial Temperature, T_i (°C)

Final Temperature, T_f (°C)

Moles of Reactant, n (mol)

Required for ΔH_rxn (kJ/mol).

What is enthalpy change?

Enthalpy change, written as ΔH, measures the heat absorbed or released by a process at constant pressure. In practical chemistry, this is one of the most useful quantities for understanding whether a process is energetically favorable and how much thermal energy moves between a system and its surroundings.

If a process absorbs heat, enthalpy increases (ΔH > 0, endothermic). If it releases heat, enthalpy decreases (ΔH < 0, exothermic).

How this calculator works

1) Heat change mode

The calculator uses:

q = m × c × ΔT
ΔT = T_f - T_i

Where:

m = mass in grams (g)
c = specific heat capacity in J/g°C
ΔT = temperature change in °C

The output is heat transfer in J and kJ. Positive q means the sample absorbed heat; negative q means it released heat.

2) Reaction enthalpy mode (calorimetry)

In many lab setups, you measure the temperature change of the solution (surroundings), then infer reaction enthalpy with opposite sign:

q_solution = m × c × ΔT
q_rxn = -q_solution
ΔH_rxn = q_rxn / n = -q_solution / n

That is why this calculator asks for moles in reaction mode and returns kJ/mol.

Step-by-step usage

Select your calculation mode.
Enter mass and specific heat capacity.
Enter initial and final temperatures.
If using reaction mode, enter moles of the limiting reactant.
Click Calculate to see q, ΔT, and ΔH (if applicable).

Sign convention quick guide

q > 0: sample/surroundings gain heat.
q < 0: sample/surroundings lose heat.
ΔH_rxn < 0: reaction is exothermic.
ΔH_rxn > 0: reaction is endothermic.

Common mistakes to avoid

Mixing units (for example, using kg with J/g°C).
Forgetting the negative sign when converting from measured solution heat to reaction enthalpy.
Using the wrong specific heat value for the material.
Rounding too early in multi-step calculations.

Worked example

Suppose 150 g of water warms from 20°C to 28°C. Use c = 4.184 J/g°C.

ΔT = 28 - 20 = 8°C
q = (150)(4.184)(8) = 5020.8 J = 5.0208 kJ

So the water absorbed 5.0208 kJ. If this came from a reaction and n = 0.0400 mol, then:

ΔH_rxn = -5.0208 / 0.0400 = -125.52 kJ/mol

Negative means the reaction is exothermic.