Which of the following is a common sign that a chemical change has occurred?

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the atomic number of carbon is six, which means that a carbon atom has six protons. carbon has three naturally occurring isotopes: carbon-12, carbon-13, and carbon-14. which of these statements are true about carbon and its isotopes? select all that appl

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.