Physical changes are changes in which no bonds are broken or formed. This means that the same types of compounds or elements that were there at the beginning of the change are there at the end of the change. Because the ending materials are the same as the beginning materials, the properties such as color, boiling point, etc. Physical changes involve moving molecules around, but not changing them.
Some types of physical changes include:. As an ice cube melts, its shape changes as it acquires the ability to flow. However, its composition does not change. Melting is an example of a physical change.
A physical change is a change to a sample of matter in which some properties of the material change, but the identity of the matter does not. When liquid water is heated, it changes to water vapor. However, even though the physical properties have changed, the molecules are exactly the same as before. We still have each water molecule containing two hydrogen atoms and one oxygen atom covalently bonded.
When you have a jar containing a mixture of pennies and nickels and you sort the mixture so that you have one pile of pennies and another pile of nickels, you have not altered the identity of the pennies or the nickels—you've merely separated them into two groups.
This would be an example of a physical change. Similarly, if you have a piece of paper, you don't change it into something other than a piece of paper by ripping it up. What was paper before you started tearing is still paper when you are done. Again, this is an example of a physical change.
Physical changes can further be classified as reversible or irreversible. The melted ice cube may be refrozen, so melting is a reversible physical change. Physical changes that involve a change of state are all reversible. Other changes of state include vaporization liquid to gas , freezing liquid to solid , and condensation gas to liquid. Dissolving is also a reversible physical change.
When salt is dissolved into water, the salt is said to have entered the aqueous state. The salt may be regained by boiling off the water, leaving the salt behind. This means that one substance with a certain set of properties such as melting point, color, taste, etc is turned into a different substance with different properties.
Chemical changes are frequently harder to reverse than physical changes. One good example of a chemical change is burning a candle. The act of burning paper actually results in the formation of new chemicals carbon dioxide and water from the burning of the wax. Another example of a chemical change is what occurs when natural gas is burned in your furnace. In this case, not only has the appearance changed, but the structure of the molecules has also changed.
The new substances do not have the same chemical properties as the original ones. Therefore, this is a chemical change. However, one must be careful; sometimes a change in color is simply the mixing of two colors, but no real change in the composition of the substances in question. When two or more compounds or elements are mixed and a scent or odor is present, a chemical reaction has taken place. For example, when an egg begins to smell, a rotten egg a chemical reaction has taken place.
This is the result of a chemical decomposition. The formation of a precipitate may be one of the most common signs of a chemical reaction taking place. A precipitate is defined to be a solid that forms inside of a solution or another solid.
Precipitates should not be confused with suspensions, which are solutions that are homogeneous fluids with particles floating about in them. For instance, when a soluble carbonate reacts with Barium, a Barium Carbonate precipitate can be observed. For further information, please refer to Classification of Matter. The formation of bubbles , or rather a gas , is another indicator of a chemical reaction taking place.
When bubbles form, a temperature change could also be taking place. Temperature change and formation of bubbles often occur together. For example, in the following image, one can see a gas spewing. This is the formation of a gas. However, most reactions are much more subtle. For instance, if the following reaction occurs, one may notice Carbon Dioxide bubbles forming. If there is enough Hydrochloric Acid, bubbles are visible.
If there isn't, one can't readily notice the change:. The viscosity image is also free to be duplicated as per permission of author on Wikipedia. This is one of the gray areas of chemical change and physical change. Although the salt has dissociated into Sodium and Chloride ions, it is still salt in water. Salt, initially is actually just a conglomerate of sodium and chloride ions and by dissociating them, just the arrangement of the ions has changed.
Please click here for more information. Introduction Physical changes are limited to changes that result in a difference in display without changing the composition. Luster Malleability Ability to be drawn into a thin wire Density Viscosity Solubility Mass Volume Any change in these physical properties is referred to as a physical change.
The following are indicators of chemical changes: Change in Temperature Change in Color Noticeable Odor after reaction has begun Formation of a Precipitate Formation of Bubbles Note: When two or more reactants are mixed and a change in temperature, color, etc. Common Physical Changes Texture The texture of a substance can differ with a physical change.
As you can see, the texture of the finished wood is much smoother than the initial grainy wood. Color The changing of color of a substance is not necessarily an indicator of a chemical change. Temperature Although we cannot see temperature change, unless if a change of state is occurring, it is a physical change. Shape The shape of an object can be changed and the object will still remain true to its chemical composition. Origami Money. Change of State The change of state is likewise a physical change.
In this instance, heat is increasing the speed of the molecules causing them move faster. If heat is removed from a substance, such as in freezing and condensation, then process is exothermic. In this instance, heat is decreasing the speed of the molecules causing them move slower. Physical Properties Luster The luster of an element is defined as the way it reacts to light. Lustrous Paperclips. Malleability Malleability is also a quality of metals.
Bent Paperclip The image shows the malleability of a certain metal as stress is applied to it. Ability to be drawn into a thin wire In materials science, this property is called ductility. Copper Wire. Oil Sinking in a Glass of Water. Viscosity Viscosity is defined to be the resistance to deformation of a particular chemical substance when a force is applied to it. Viscosity of Fluids Figure 1. The fluid on the left has a lower viscosity than the fluid on the right. Common Chemical Changes The follow are all indicators of chemical reactions.
Change in Temperature A change in temperature is characteristic of a chemical change. Change in Color A change in color is also another characteristic of a chemical reaction taking place. Metal Rusting The reaction above is that of the rusting of iron. Did you know that scientists, nature and even you can change one material into another? In a chemical reaction matter is changed from one substance from one to another.
Burning wood changes the wood into ash. Water will react with iron to form a new product. Do you know what it is? If you have ever left your bicycle in the rain you probably know it is called rust. Chemical reactions may also produce heat, light, bubbles or color changes. When the bike rusted, the metal turned a different color so we know that a chemical reaction occurred between the bike and the water.
Please remember that not all color changes prove that a chemical reaction has taken place. A physical change is different than a chemical change. Things that are changed physically do not turn into something else. Breaking a match in two pieces is an example of a physical change. Lighting a match and letting is burn is an example of a chemical change. Chemical reactions cause chemical changes.
In a chemical reaction two or more substances , called the reactants, form different substances called products. In the above examples the wood and oxygen were the reactants that, when heated, formed the products of ash and smoke gases.
Water, iron and oxygen were the reactants that formed the product called rust. What would happen if you were to change one of the reactants in a chemical reaction? What if, instead of water, you put grease or oil on your bike? Would you still get rust? Of course not.
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