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![Signs of Chemical Change
A chemical change can be recognized by the following
indicators [1-4]
:
1. Change in Temperature
A chemical change accompanies a change in energy. Since a
chemical change involves energy, there can also be a
temperature change. The change is exothermic if heat is given
off during the reaction. When heat is absorbed, it is called an
endothermic reaction. For example, a thermite reaction is
accompanied by a temperature increase (exothermic).](https://image.slidesharecdn.com/changesofmaterials-memenmegawide-250622174359-c33e2edc/85/CHANGES-OF-MATERIALS-power-point-presentation-6-320.jpg)
CHANGES OF MATERIALS power point presentation
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- 2. PHYSICAL CHANGE are changesaffecting the form of a chemical substance, but not its chemical composition. Physical changes are used to separate mixtures into their component compounds, but can not usually be used to separate compounds into chemical elements or simpler compounds.
- 4. CHEMICAL CHANGE occurwhen a substance combines with another to form a new substance, called chemical synthesis or, alternatively, chemical decomposition into two or more different substances. These processes are called chemical reactions and, in general, are not reversible except by further chemical reactions.
- 6. Signs of ChemicalChange A chemical change can be recognized by the following indicators [1-4] : 1. Change in Temperature A chemical change accompanies a change in energy. Since a chemical change involves energy, there can also be a temperature change. The change is exothermic if heat is given off during the reaction. When heat is absorbed, it is called an endothermic reaction. For example, a thermite reaction is accompanied by a temperature increase (exothermic).
- 7. 2. Changein Color An example of color change in a chemical reaction is rusting. Rusting occurs when iron reacts with oxygen in the presence of moisture to form reddish-brown iron (III) oxide, commonly known as rust. 3. Noticeable Odor When two substances react or when a substance decomposes and produces a distinct odor, it indicates a chemical change. For example, the decomposition of an egg gives a foul smell.
- 8. 4. Formationof Precipitate The formation of a precipitate is the most common sign of a chemical change. A precipitate is a solid that forms during a chemical reaction and does not go into the solution. It either settles at the bottom or remains suspended. For example, when the aqueous salt of silver (I) nitrate combines with sodium chloride salt solution, a white precipitate of silver(I) chloride forms. 5. Formation of Bubbles Bubble formation is also an indicator of a chemical change. It is generally accompanied by temperature change. For example, the reaction between sodium carbonate and hydrochloric acid results in the formation of carbon dioxide gas, which is observed as bubbles.
- 9. Group Activity GroupA-Get a piece of paper . Crumple it and explain. Group B_ Get the egg, break it. What will happened to the egg? Is there a change? Explain it Group C- Chopping a carrot/ apple. What can you say about it?
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- 11. Question and Answer 1. Classify the following as Chemical or Physical change. Tearing a piece of paper 100 times. A. Physical Change B. Chemical Change 2.Burning a piece of paper A. Chemical Change B. Physical Change 3. Classify the following as a physical or chemical change: A reaction occurs, and the product is different from what you started with. A. Physical Change B. Chemical Change 4. Hammering a nail into a piece of wood A. Physical Change B. Chemical Change 5. Letting the nail rust. A. Physical Change B. Chemical Change
- 12. What isthe difference between a physical and chemical change in one sentence? Summary. Chemists make a distinction between two different types of changes that they study—physical changes and chemical changes. Physical changes are changes that do not alter the identity of a substance. Chemical changes are changes that occur when one substance is turned into another substance. In a physical change the appearance or form of the matter changes but the kind of matter in the substance does not. However in a chemical change, the kind of matter changes and at least one new substance with new properties is formed.
- 13. Assignment: By group: 1. You combine two clearly liquids and they turn cloudy white. 2. You put a yellow liquid and a blue liquid together, and they become green 3. Cutting an apple in half.