Part 4 of Chapter 1 in Chemistry

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(Again using ' ' for definition words) The book's chapter in this lesson starts with "'Physical properties' of matter are those properties that can usually be observed with our senses. They include everything about a substance that can be noted when no change is occurring in the type of structure that makes up its smallest component. Some examples are physical state, color, odor, solubility in water, density, melting point, taste, boiling point, and hardness. 'Chemical changes' are those properties that can be observed with regard to whether or not a substance changes chemically, often as a result of reacting with other substances. For example, iron rusts in most air, nitrogen does not burn, gold does not rust, sodium reacts with water, and water can be decomposed by an electric current." Next it writes about Chemical and Physical Changes. It gives a note to remember that " Physical change does not alter the identity of the substance, Chemical change does." It also says, "The changes matter undergoes are classified as either physical or chemical. In general, a 'physical change' alters the physical properties of matter, but the composition remains constant. The most often altered properties are form and state. Some examples are breaking glass, cutting wood, melting ice, and magnifying a piece of metal. In some cases, the process that caused the change can be easily reversed and the substance regains its original form. 'Chemical changes' are changes in the composition and structure of a substance. They are always accompanied by energy changes. If the energy released in the formation of a new structure exceeds the chemical energy in the original substances, energy will be given off, usually in the form of heat or light or both. This is called 'exothermic reaction. This can be shown graphically. If, however, the new structure needs to absorb more energy than is available from the reactants, the result is an 'endothermic reaction'. This can be shown graphically. Grandma will stop here and cover the rest in another lesson. We are only halfway through the chapter and have exercises to do.