Endothermic Reaction
A reaction that absorbs energy from the surroundings, giving a positive enthalpy change.
Formula / equation
ΔH > 0
Unit
kJ/mol
In depth
More energy is required to break the reactant bonds than is recovered when product bonds form, so the surroundings cool. Endothermic reactions become spontaneous only when the entropy increase is large enough that TΔS exceeds ΔH, which is why many require heating.
Examples in the real world
Thermal decomposition of limestone; photosynthesis; ammonium nitrate dissolving in water in an instant cold pack.