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Chemical and Physical Properties How to tell the difference

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Physical properties Inherent characteristics of a substance that can be determined without altering its composition Associated with its physical existence Color, taste, odor, state of matter (solid, liquid, or gas), density, melting point, boiling point.

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Chemical Properties Describe the ability of a substance to form new substances, either by reaction with other substances or by decomposition. Will it burn? Will it combine with this substance to form something new?

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Chemical property or physical property? Fluorine gas has a greenish-yellow tint. Physical property The density of water at 4 degrees C is 1.000 g/mL. Physical property Hydrogen gas is very flammable. Chemical property

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Chemical property or physical property? Aluminum is a solid at 25 degrees C. Physical property Water is colorless and odorless. Physical property Lemon juice tastes sour. Physical property Gold does not tarnish Chemical property Copper cannot be decomposed. Chemical property

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Chemical Changes Chemical changes take place on the molecular level. A chemical change produces a new substance. Examples of chemical changes include combustion (burning), cooking an egg, rusting of an iron pan, and mixing hydrochloric acid and sodium hydroxide to make salt and water.

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Physical Changes Physical changes are concerned with energy and states of matter. A physical change does not produce a new substance. Changes in state or phase (melting, freezing, vaporization, condensation, sublimation) are physical changes. Examples of physical changes include crushing a can, melting an ice cube, and breaking a bottle.

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How to Tell Chemical & Physical Changes Apart A chemical change makes a substance that wasn't there before. There may be clues that a chemical reaction took place, such as light, heat, color change, gas production, odor, or sound. The starting and ending materials of a physical change are the same, even though they may look different.

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Chemical Changes will include at least one of these: Color change Fire/smoke produced Odor produced Gas (bubbles) produced Temperature change w/o a heat source

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Chemical or physical change? Polystyrene + acetone Physical because the polystyrene is dissolved (melts) but does not change identity A few grams of sucrose + deionized water Chemical, since the sucrose dissolves and interacts with the water

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Chemical or physical change? A copper statue, over time, turns green Chemical, since the copper has reacted with oxygen to form copper oxide When a teaspoon of baking soda (sodium bicarbonate) is placed into a few ounces of vinegar (acetic acid), volumes of bubbles (effervescence) are produced Chemical, since gas is produced, an indicator that there is a chemical reaction occurring

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Chemical or physical change? When a few grams of a blue crystalline solid are placed into a beaker of deionized water, the crystals disappear and the liquid becomes clear and blue in color Physical, since the blue crystalline solid turns to liquid, but retains its blue color, and the water retains its clear color, indicating that they are a homogeneous mixture and dont interact, but the crystals have dissolved

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Chemical or physical change? In the lab, a student mixes 2mL of NaOH (sodium hydroxide) with 2mL of HCl (hydrochloric acid) in a test tube. He notices that the test tube has become very warm to the touch. Chemical, since the generation of heat is an indication that there is a chemical reaction occurring

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Chemical or physical change? A woman visits a hairdresser and has her hair colored a darker shade of brown. After several weeks the hair, even though washed several times, has not changed back to the original color. Chemical change, since there has been a change in the appearance of the hair that indicates that the strands of hair have been changed

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Chemical or physical change? Sulfur + Iron + HEAT = Iron sulfide, a new substance with new properties so its a CHEMICAL change