physical and chemical change


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OBJECTIVES This presentation is to show the differences between physical and chemical changes, it’s to show us a variety of chemical change indicators, and to help us begin to see the beginnings of real chemistry. Students will understand that chemical and physical changes occur in matter.



Physical Change:

Physical Change The substance involved remains the same, even though it may change state or form. Ex. Pour melted chocolate on ice cream. It still tastes the same because the particles have not changed, it just hardened (changed state) because the ice cream was cool.

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Physical Change

Chemical Change:

Chemical Change Chemical Changes: The original substance is changed into one or more different substances that have different properties. Examples: Burning, Cooking, Rusting… The formation of water from hydrogen and oxygen. The formation of rust from iron and oxygen.

There are usually clues that a chemical change has happned::

There are usually clues that a chemical change has happned : A new color appears. Heat or light is given off. Bubbles of gas are given off. A solid material (called a precipitate) forms in a liquid. The change is difficult to reverse.

Types of Chemical Change:

Types of Chemical Change Synthesis --  purposeful execution of chemical reactions to get a product , or several products. This happens by physical and chemical manipulations usually involving one or more reactions. In modern laboratory usage, this tends to imply that the process is reproducible, reliable, and established to work in multiple laboratories. Decomposition -- the separation of a chemical compound into elements or simpler compounds. It is sometimes defined as the exact opposite of a chemical synthesis . Chemical decomposition is often an undesired chemical reaction . The stability that a chemical compound ordinarily has is eventually limited when exposed to extreme environmental conditions like heat , radiation , humidity or the acidity of a solvent .

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Single displacement also called single-replacement reaction , is a type of oxidation-reduction chemical reaction when an element or ion moves out of one compound and into another. (One element is replaced by another in a compound.) This is usually written as A + BX → AX + B Metathesis reaction a molecular process involving the exchange of bonds between the two reacting chemical species , which results in the creation of products with similar or identical bonding affiliations. [1] This is represented by the general reaction scheme: AX + BY → BX + AY These chemical species can either be ionic or covalent. When referring to precipitation reactions between solutions of ions in inorganic chemistry, these were formerly referred to as double displacement or double replacement reactions , though these terms are still encouraged.

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Neutralization is a chemical reaction whereby an acid and a base react to form a salt . Water is also produced in netrualizations with Arrhenius acids and Arrhenius bases , which contain an H+ and an OH- group respectively, though it is not produced in all acid-base reactions, such as a neutralization of ammonia . Precipitation the formation of a solid in a solution or inside another solid during a chemical reaction or by diffusion in a solid. When the reaction occurs in a liquid, the solid formed is called the precipitate , or when compacted by a centrifuge , a pellet . The liquid remaining above the solid is in either case called the supernate or supernatant . Powders derived from precipitation have also historically been known as flowers .

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Combustion or burning is the sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat and conversion of chemical species. The release of heat can result in the production of light in the form of either glowing or a flame . Fuels of interest often include organic compounds (especially hydrocarbons ) in the gas, liquid or solid phase. Redox (shorthand for oxidation-reduction ) reactions describe all chemical reactions in which atoms have their oxidation number ( oxidation state ) changed. This can be either a simple redox process, such as the oxidation of carbon to yield carbon dioxide (CO 2 ) or the reduction of carbon by hydrogen to yield methane (CH 4 ), or a complex process such as the oxidation of sugar (C 6 H 12 O 6 ) in the human body through a series of complex electron transfer processes. Oxidation is the loss of electrons or an increase in oxidation state by a molecule , atom , or ion . Reduction is the gain of electrons or a decrease in oxidation state by a molecule, atom, or ion.

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Hmm…I remember in lab shaping the play dough into different forms was a physical change! And I remember that when the cake batter reacts with oxygen in the oven and bakes into a cake, it is a chemical reaction…a new substance has formed! The End


BSED- II Jonathan V. Raby