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Physical and Chemical Changes

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by

Amy Nguyen

on 28 May 2013

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Transcript of Physical and Chemical Changes

Physical and Chemical Changes By: Amy Nguyen, Crystal Rubio, and Natalie Popov You can tell when a chemical change has taken place if... Chemical changes are almost impossible to reverse. For example, once a firework explodes, it cannot be reversed, even if you attempt to gather all of the remaining bits of the firework to recreate it. As a firework explodes, new chemicals are formed and light and energy is released; if these newly formed chemicals were put back together, the initial composition of the firework can not be reproduced. Thank you for listening and watching! Baking Brownies... What are physical and chemical changes? What are signs of chemical change? Reversibility of Chemical Changes Sketches A physical Change is a change from one state of matter to another without a change in chemical composition. A chemical Change is a change between one or more substances that result in entirely new substances that contain different properties. What's the difference? In physical changes, the identity/chemical composition of the matter does NOT change, new substances are NOT produced, and they are EASILY reversed. In chemical changes, the chemical composition of the matter DOES change, new substances with different properties ARE formed, and they are DIFFICULT to be reversed. Physical Changes Like we've mentioned before, physical changes are changes in which no new substances are formed. For example, when ice cubes are melted, their shapes and sizes may have changed, but they are still made of water. Another example can be seen through ice cream. If you are eating your ice cream outside on a hot summer day, the ice cream will begin to melt and turn into a liquid. However, this liquid is still composed of the ingredients that make up ice cream. When mixing lemonade powder with water, the powder may seem to dissolve into the water, however, no change in the composition in either the water or powder had taken place. What are the different types of physical changes? The five main physical changes are...
cutting
melting
freezing
blending
dissolving
boiling During a physical change, the physical properties of the matter changes. A physical property is a characteristic that can be observed without a change in the matter's identity. More about Physical Properties Physical properties can be used to describe physical changes. These properties include: Reversibility Ductility - ability to be drawn into wires
Thermal/Electrical Conductivity - ability of a substance to conduct heat
Malleability - ability to be rolled or pounded into different shapes
Solubility - ability to dissolve into something (usually a substance)
and the substances'...
State
Density - mass/volume
Flexibility
Size
Color
Hardness Chemical Changes Due to the fact that the identity of the matter does not change during a physical change, most physical changes are easy to reverse. For example: In all chemical changes, new substances with different properties are formed. When an ice cube is left in the sun, the heat from the sun will will melt the ice cube... However, if you were to the liquid and put it into an ice tray inside the freezer, and eventually, all that is left is water. after a couple of hours, the water will freeze and retain its original shape and form as an ice cube. For example, when live bacterial cultures are added to milk, after a certain amount of time, the milk and bacteria will develop a type of acid that helps to form a new, thicker substance: yogurt. Another example can be seen through mixing vinegar and baking soda. The vinegar reacts with the baking soda and creates a new gas substance: carbon dioxide. and result in a totally different substance: denser and thicker brownies! When making brownies, you combine ingredients, such as eggs, sugar, and flour to create a raw batter. Once the batter is put into a heated oven, the ingredients will react with the heat A substance's odor, taste, or color changes
Fizzing/bubbles appear
Sound/light is emitted
Heat is emitted or absorbed by the substance
A change in melting point or boiling point occurs Soured milk - if a carton of milk is not finished by the expiration date, the milk will sour. As the milk sours, both the taste and smell of the milk will change.
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