The symptoms of hay fever include: 1  frequent sneezing. 2  runny or blocked nose. 3  itchy, red or watery eyes (allergic conjunctivitis)  an itchy throat, mouth, nose and 1  ears. cough, caused by postnasal drip (mucus dripping down the throat from the back of the nose)
Definition. noun, plural: chemical reactions. A process in which one or more substances (reactants) are chemically changed into one or more new substances (products).Chemical changes may involve motion of electrons in the forming and breaking of chemical bonds.Supplement. process in which one or more substances (reactants) are chemically changed into one or more new substances (products). Chemical changes may involve motion of electrons in the forming and breaking of chemical bonds. Supplement.
Combustion Reaction Defined. Chemical reactions are very common. A chemical reaction is any process by which the atoms of one or more substances are rearranged to form different substances.There are numerous types of chemical reactions.ombustion reactions are very common because oxygen readily reacts with many substances. One combustion reaction that has been very important throughout history is the burning of coal.