Endothermic+Reactions

In thermodynamics, the word endothermic ("within-heating") describes a process or reaction in which the system absorbs energy from the surroundings in the form of heat. It is a modern coinage formed from Greek roots (as is often the case with scientific terminology). The prefix endo- derives from the Greek word "endon" (ἔνδον) meaning "within," and the latter part of the word comes from the Greek word root "therm" (θερμ-) meaning "hot." Hence it refers to a reaction that needs heat. The opposite of an endothermic process is an exothermic process, one that releases energy in the form of heat. Thus in each term (endothermic & exothermic) the prefix refers to where heat goes as the reaction occurs. The term endothermic was coined by Marcellin Berthelot (25 October 1827 – 18 March 1907). The concept is frequently applied in physical sciences to, for example, chemical reactions, where thermal energy (heat) is converted to chemical bond energy.

  Endothermic reactions cannot occur spontaneously. Work must be done in order to get these reactions to occur. When endothermic reactions absorb energy, a temperature drop is measured during the reaction. Endothermic reactions are characterized by positive heat flow (into the reaction) and an increase in enthalpy (+ΔH).  Photosynthesis is an example of an endothermic chemical reaction. In this process, plants use the energy from the sun to convert carbon dioxide and water into glucose and oxygen. This reaction requires 15MJ of energy (sunlight) for every kilogram of glucose that is produced: sunlight + 6CO 2 (g) + H 2 O(l) = C 6 H 12 O 6 (aq) + 6O 2 (g)