By Claire Gillespie – Updated August 30, 2022

Some chemical reactions release heat, transferring thermal energy to their surroundings. These are called exothermic reactions, where “exo” means external and “thermic” refers to heat.

Common exothermic processes include combustion (burning), oxidation (rusting), and neutralization between acids and bases. Everyday items such as hand warmers and self‑heating coffee cans rely on these reactions.

Quick Reference

To determine the heat released, use the formula Q = m·c·ΔT:

• Q – heat energy transferred (J)
• m – mass of the liquid or substance (kg)
• c – specific heat capacity (J kg⁻¹ °C⁻¹)
• ΔT – temperature change (°C)

Heat vs. Temperature

Temperature measures how hot an object is (°C or °F). Heat is the amount of thermal energy an object contains, expressed in joules. When heat is added, temperature rises depending on the object's mass, composition, and the energy supplied.

Specific Heat Capacity

The specific heat capacity (c) is the energy needed to raise 1 kg of a substance by 1 °C. Examples:

• Water: 4,181 J kg⁻¹ °C⁻¹
• Oxygen: 918 J kg⁻¹ °C⁻¹
• Lead: 128 J kg⁻¹ °C⁻¹

Heat Energy Calculator

To compute the energy required to change a substance’s temperature:

Q = m × c × ΔT

Where Q is energy in joules, m is mass in kilograms, c is specific heat capacity in J kg⁻¹ °C⁻¹, and ΔT is the temperature change in °C.

Heat Released Calculator – Example

Suppose 100 g of an acid is mixed with 100 g of a base, raising the temperature from 24 °C to 32 °C.

The neutralization reaction can be simplified to:
H⁺ + OH⁻ → H₂O

Calculations:

• Mass: (100 g + 100 g) ÷ 1000 = 0.2 kg
• Specific heat capacity of water: 4,186 J kg⁻¹ °C⁻¹
• ΔT: 32 °C – 24 °C = 8 °C
• Q = 0.2 kg × 4,186 J kg⁻¹ °C⁻¹ × 8 °C = 6,688 J

Thus, 6,688 joules of heat are released.