A microreactor for performing chemical reactions, includes a body, a first chamber and a second chamber, both formed in the body. Interconnections are provided for fluidly coupling the first chamber and the second chamber through the body. The microreactor also includes a venting passage formed in the body and having a venting outlet in the second chamber and at least one venting inlet in the first chamber, at a location where formation of bubbles is expected upon introduction of a liquid in the first chamber.