1. In chemistry, a chemical reaction that occurs spontaneously without external constraint or control
The free reaction between hydrogen and oxygen produces water and heat.
A reação livre entre hidrogênio e oxigênio produz água e calor.
2. In psychology or social contexts, an uncontrolled or spontaneous emotional or behavioral response
His free reaction to the news showed genuine surprise.
Sua reação livre à notícia mostrou surpresa genuína.