An atom in its ground state is excited when it absorbs a single photon of light. The atom then relaxes back to the ground state by emitting two photons, the first, a red photon at 700 700 nm, and the second, an infrared photon at 2100 nm. What is the wavelength of the absorbed photon?

chemical changes occur when a substance combines with another to form a new substance, called chemical synthesis or, alternatively, chemical decomposition into two or more different substances. these processes are called chemical reactions and, in general, are not reversible except by further chemical reactions. some reactions produce heat and are called exothermic reactions and others may require heat to enable the reaction to occur, which are called endothermic reactions. understanding chemical changes is a major part of the science of chemistry.