State the difference between mass and weight

Mass is the measurement of what amount of matter is contained in an object. Whereas

weight is the measurement the pull of gravity on an object.

Another way to differentiate both is Mass is measured on a balance comparing a known amount a matter of to an unknown amount of matter and weight is measured on a scale.

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.