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Physical And Chemical Changes

Check us out at http://www.tutorvista.com//videos Physical change is a concept introduced to contrast with the concept of chemical change. A physical change is any change not involving a change in the substance's chemical identity. Matter undergoes chemical change when the composition of the substances changes: one or more substances combine or break up (as in a relationship) to form new substances. Physical changes occur when objects undergo a change that does not change their chemical nature. A physical change involves a change in physical properties. Physical properties can be observed without changing the composition of matter. Examples of physical properties include: texture, shape, size, color, volume, mass, weight, and density. An example of a physical change occurs when making a baseball bat. Wood is carefully crafted into a shape which will allow a batter to best apply force on the ball. Even though the wood has changed shape and therefore physical properties, the chemical nature of the wood has not been altered. The bat and the original piece of wood are still the same chemical substance. Changes are sometimes hard to categorize strictly as physical or as chemical. Dissolving a salt in water involves the breaking of chemical bonds, yet is often described as a physical change. Some teachers hold that a chemical change is a rearrangement of atoms, but many physical changes also involve the rearrangement of atoms. Many chemical changes are irreversible, and many physical changes are reversible, but reversibility is not a certain criterion for classification. Although chemical changes are often recognized by an indication such as odor, color change, production of a precipitate, or production of a gas, every one of these indicators can result from physical change. chemical change, bonds are broken and new bonds are formed between different atoms. This breaking and forming of bonds takes place when particles of the original materials collide with one another. Some exothermic reactions may be hot enough to cause certain chemicals to also undergo a change in state; for example in the case of aqueous solutions, bubbles may not necessarily be newly produced gas but instead water vapor. Whenever chemical reactions occur, the atoms are rearranged and the reaction is accompanied by an energy change as new products are generated. An example of a chemical change is the reaction between sodium hydroxide and hydrogen chloride to produce sodium chloride, or table salt. This reaction is so exothermic, meaning it releases heat in the form of energy, that even flames are generated. This is an example of a chemical change because the end product is molecularly different from the starting molecules. Chemical changes are happening all the time. There are several different types of chemical change, including: synthesis, decomposition, single displacement, double displacement, neutralization, precipitation, combustion and redox.
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