Thermochemistry Calculator

The fundamental equation of calorimetry relates heat, mass, specific heat capacity, and temperature change:

q = m × c × ΔT

Where q is the heat transferred (joules), m is the mass (grams), c is the specific heat capacity of the substance (J/g·°C), and ΔT = T_final − T_initial.

If ΔT is positive the temperature went up, so q is positive and the substance absorbed heat. That is an endothermic process.
If ΔT is negative, q is negative and heat was released. That is exothermic.

Specific heat capacities (J/g·°C):

• Water (liquid): 4.184, the highest of any common substance, which is what makes water such an effective heat sink
• Ice: 2.093
• Steam: 2.01
• Ethanol: 2.44
• Concrete / sand: 0.84
• Aluminum: 0.897
• Iron: 0.449
• Copper: 0.385, and a low specific heat is why copper heats up so fast
• Silver: 0.233
• Gold: 0.129, the lowest of the metals listed here

Water’s exceptionally high specific heat is why coastal climates are milder than inland ones, why oceans buffer climate change, and why water is used as a coolant in engines and nuclear reactors.

One number only holds inside one phase

This is the part beginners miss, and the calculator now checks it. Each of those values belongs to a single phase of the substance. Liquid water’s 4.184 applies between 0 and 100°C and nowhere else. Ask for water from 20 to 150°C and the arithmetic will happily produce a number, but the real process boils partway through, and boiling absorbs a large amount of heat at a constant temperature that q = mcΔT knows nothing about.

For reference, vaporizing water takes 2,260 J/g, which is more than five times the energy needed to raise the same gram from freezing to boiling. Melting ice takes 334 J/g. When a calculation crosses a phase boundary you need those latent heats as separate terms.

Metals have the same limit at the other end of the scale. Aluminum melts at 660°C, copper at 1,085°C, gold at 1,064°C, silver at 962°C, iron at 1,538°C. Concrete never really melts, but the cement paste starts to dehydrate and spall somewhere above 300 to 600°C, so treating it as a single solid past that point is optimistic.

A worked example

How much energy does it take to heat 500 g of water from 20°C to 100°C?

q = 500 × 4.184 × 80 = 167,360 J = 167.36 kJ

That is 0.0465 kWh. At 17 cents per kilowatt-hour, roughly the US residential average in 2025, it costs about 0.8 cents. Electricity prices move every year and vary enormously by state and country, so the calculator asks you for your own rate rather than assuming one.

The sign of q matters: negative q means heat flows out of the system into the surroundings. Exothermic reactions such as combustion and neutralization release heat, while endothermic ones such as dissolving ammonium nitrate absorb it.