1. A visible or expressed response to something, without restraint or concealment
Her open reaction to the news surprised everyone in the room.
A reação aberta dela à notícia surpreendeu todos na sala.
2. In chemistry, a reaction that occurs in an open system, exposed to the atmosphere
The combustion of fuel is an open reaction that releases gases into the air.
A combustão do combustível é uma reação aberta que libera gases no ar.
3. A candid or unguarded emotional response
His open reaction showed genuine emotion without any pretense.
A reação aberta dele mostrou emoção genuína sem qualquer pretensão.