What Is a Chemical Reaction?

Tell which of the following are chemical changes: (a) fermenting sugar, (b) winding a clock spring, (c) burning wood, (d) evaporating ether, (e) cooking meat, (f) dissolving sugar, (g) mixing sand and salt, and (h) rusting iron. When a chemical change occurs it changes the chemical composition of the original substances and through bonding form a new substance. Fermenting sugar, burning wood, cooking meat, and rusting iron are all considered chemical changes; they have changed the chemical composition of the substances and formed new ones.

What happens to the reacting substances in chemical reactions? When involved in chemical reactions the reacting substances bond are broken and then reformed differently. The reacting substances properties change and a new substance is then formed. 5. What is the difference between an endothermic reaction and an exothermic reaction? The difference between an endothermic reaction and an exothermic reaction lies in where the energy produced in a reaction goes. In exothermic reactions the heat or energy is released into the surrounding environment. In endothermic reactions heat or energy is absorbed in order for the reaction to occur, not releasing heat or energy. Questions and Problems:

Give three examples of exothermic reactions from everyday life. Three examples of exothermic reactions in everyday life are the lighting of a match, turning on a light, and burning wood. All of these reactions release energy and give off heat when they occur. Hard water deposits are largely CaCO . Suggest a way to remove these deposits from plumbing fixtures.

When you added Hydrochloric acid to iron, what gas was formed? Give its name and formula and the number of atoms in each molecule. When hydrochloric acid and iron are mixed it produces a gas called Iron (II) Chloride and hydrogen.

Iron + Hydrochloric acid
Iron (II) Chloride + dihydrogen.