A pouch for internal mixture of segregated reactants includes an outer containment envelope with a sealed reactant compartment inside. A middle shear strip and two outer strips, together defining two shear lines, are connected to the reactant compartment. The outer strips are folded under the reactant compartment with their tips anchored to the containment envelope. The middle strip extends away from the reactant compartment and through a slit in the containment envelope. Pulling on the middle strip causes the shear lines to lengthen until the reactant compartment is shorn open to release a reactant. A permeable second reactant compartment containing a second reactant may also be disposed inside the containment envelope, and may include a slit through which the middle strip passes. The reaction in the pouch may be exothermic and the pouch may be applied to any object to be heated such as a wet wipes dispenser.