An active intermediate molecule is a highly energetic and reactive molecule that is short-lived, disappearing virtually as fast as it is formed. These molecules are present in very low concentrations and have a very short lifespan, typically on the order of 10^-14 seconds. The net rate of reaction of an active intermediate is zero, and the assumption that the net rate of reaction is zero is called the Pseudo Steady State Hypothesis (PSSH). In chemistry, a reactive intermediate or an intermediate is a short-lived, high-energy, highly reactive molecule. When generated in a chemical reaction, it will quickly convert into a more stable molecule. Only in exceptional cases can these compounds be isolated and stored, e.g. at low temperatures or through matrix isolation. Adenosine triphosphate (ATP) is also an example of an active intermediate and can be thought of as the main energy currency of cells, powering many energy-requiring cellular reactions.