Physical vs. Chemical Changes PDF

*Physical vs. Chemical change* 09/02 A physical change means altering a substance\'s appearance or state (like melting ice) **WITHOUT CREATING A NEW SUBSTANCE.** It is also REVERSIBLE, i.e. If you melt an ice cube in a bowl, you can put it in the freezer and it will turn back into ice. Solid Liqu...

*Physical vs. Chemical change* 09/02 A physical change means altering a substance\'s appearance or state (like melting ice) **WITHOUT CREATING A NEW SUBSTANCE.** It is also REVERSIBLE, i.e. If you melt an ice cube in a bowl, you can put it in the freezer and it will turn back into ice. Solid Liquid Solid A chemical change involves forming **A NEW SUBSTANCE** with different properties than the substances used to create it. It involves a chemical change within the original substance, i.e. frying an egg (forming new chemical bonds within the proteins). You cannot reverse a chemical change, i.e. you cannot un-bake a cake or un-fry an egg. *How do I know when a change is chemical or physical?* A physical change is often categorized using words such as: - Melting - Evaporation - Boiling - Condensation - Crystallization - Action words e.g. mixing, crushing, etc. A chemical change is indicated by: - Change in or production of energy (light, heat, sound, etc.) - Color change - Formation of gas bubbles - Change in taste, density, smell or temperature You must visualize the reaction in your head in order to determine whether a change is chemical or physical based on the indicators of each change. This can get complicated when comparing physical and chemical change but think about each factor individually. For example, think about a nail rusting. The nail still remains metal, so you might think this is a physical change. However, rust (*FeO*) forms on the nail. Think about the original nail vs. the rusted nail. Does it change color? Does it smell different? *Other examples of chemical change are baking a cake, digestion, a rotting apple, vinegar and baking soda solution.* [Exercise:] Determine whether the following changes are chemical or physical and explain your answer. 1. Baking a cake 2. Burning wood 3. Melting ice cream 4. Digesting food 5. Crushing a soda can 6. Cutting a piece of paper 7. Boiling water 8. Combining hydrogen and oxygen to form water 9. Mixing sand and marbles 10. Using a battery  Mixtures, Elements and Compounds ================================ An element is a pure substance (cannot be broken down into other substances), i.e. Oxygen (*O*) Hydrogen (*H*) Iron (*Fe*) A compound is a substance made when two or more ELEMENTS are CHEMICALLY BONDED together, i.e. Water H₂O, Table salt NaCl, Sodium carbonate Na₂CO₃ A mixture is a substance consisting of two or more substances NOT CHEMICALLY COMBINED together. You can have mixtures of elements, mixtures of compounds, or mixtures containing both. You can also separate mixtures via methods such as sieving, evaporation, distillation, hand sorting & more. i.e. Milk, water and sand, air, salt water. *\*Quiz\**