Processes and devices for delivering a fluid by chemical reaction are disclosed. A chemical reaction is initiated in a reaction chamber to produce a gas, and the gas acts upon a piston to deliver the fluid. Preferred devices typically include an upper chamber, a lower chamber, a fluid chamber, a piston between the lower chamber and the fluid chamber, and a barrier between the upper chamber and the lower chamber. When the barrier is broken, reagents in the upper chamber and the lower chamber are mixed together to generate the gas.