Typical types of change include the processes involved in photosynthesis, a process in which carbon dioxide and water are changed into sugars and oxygen by plants, digestion in which energy rich materials are used by organisms to grow and move, the Krebs cycle which liberates energy from stored reserves, protein synthesis which enables organisms to grow using processes controlled by RNA, etc. Evidence of a chemical change The following can indicate that a chemical change has taken place, although this evidence is not conclusive: Change of odor. Change of color (for example, silver to reddish-brown when iron rusts). Change in temperature or energy, such as the production (exothermic) or loss (endothermic) of heat. Change of composition - paper turning to ash when burned. Light and/or heat given off. Formation of gases, often appearing as bubbles in liquids. Formation of a precipitate (insoluble particles). The decomposition of organic matter (for example, rotting food). The change is difficult or impossible to reverse. References Chemical reactions Change