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Burn

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Physical change

Ice into water

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3.2. Chemical ChangeChemical changes occur when bonds are broken and/or formed between molecules or atoms. 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, to be exact) from the burning of the wax. Another example of a chemical change is what occurs when natural gas is burned in your furnace. This time, on the left we have a molecule of methane, CH4CH4, and two molecules of oxygen, O2O2, while on the right we have two molecules of water, H2OH2O, and one molecule of carbon dioxide, CO2CO2. 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. Figure 3.6.23.6.2: Burning of wax to generate water and carbon dioxide is a chemical reaction. Image used with permission (CC-SA-BY-3.0; Andrikkos )We can't actually see molecules breaking and forming bonds, although that's what defines chemical changes. We have to make other observations to indicate that a chemical change has happened. Some of the evidence for chemical change will involve the energy changes that occur in chemical changes, but some evidence involves the fact that new substances with different properties are formed in a chemical change.Observations that help to indicate chemical change include:•	Temperature changes (either the temperature increases or decreases)•	Light is given off•	Unexpected color changes (a substance with a different color is made, rather than just mixing the original colors together)•	Bubbles are formed (but the substance is not boiling - you made a substance that is a gas at the temperature of the beginning materials, instead of a liquid)•	Different smell or taste (do not taste your chemistry experiments, though!)•	A solid forms if two clear liquids are mixed (look for floaties - technically called a precipitate)

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3.2. Chemical ChangeChemical changes occur when bonds are broken and/or formed between molecules or atoms. 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, to be exact) from the burning of the wax. Another example of a chemical change is what occurs when natural gas is burned in your furnace. This time, on the left we have a molecule of methane, CH4CH4, and two molecules of oxygen, O2O2, while on the right we have two molecules of water, H2OH2O, and one molecule of carbon dioxide, CO2CO2. 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. Figure 3.6.23.6.2: Burning of wax to generate water and carbon dioxide is a chemical reaction. Image used with permission (CC-SA-BY-3.0; Andrikkos )We can't actually see molecules breaking and forming bonds, although that's what defines chemical changes. We have to make other observations to indicate that a chemical change has happened. Some of the evidence for chemical change will involve the energy changes that occur in chemical changes, but some evidence involves the fact that new substances with different properties are formed in a chemical change.Observations that help to indicate chemical change include:•	Temperature changes (either the temperature increases or decreases)•	Light is given off•	Unexpected color changes (a substance with a different color is made, rather than just mixing the original colors together)•	Bubbles are formed (but the substance is not boiling - you made a substance that is a gas at the temperature of the beginning materials, instead of a liquid)•	Different smell or taste (do not taste your chemistry experiments, though!)•	A solid forms if two clear liquids are mixed (look for floaties - technically called a precipitate)

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3.1.Physical ChangePhysical 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) will also be the same. Physical changes involve moving molecules around, but not changing them. Some types of physical changes include:•	Changes of state (changes from a solid to a liquid or a gas and vice versa)•	Separation of a mixture•	Physical deformation (cutting, denting, stretching)•	Making solutions (special kinds of mixtures)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 we heat the liquid water, it changes to water vapor. But 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 either 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're done. Again, this is an example of a physical change. 

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3.1.Physical ChangePhysical 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) will also be the same. Physical changes involve moving molecules around, but not changing them. Some types of physical changes include:•	Changes of state (changes from a solid to a liquid or a gas and vice versa)•	Separation of a mixture•	Physical deformation (cutting, denting, stretching)•	Making solutions (special kinds of mixtures)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 we heat the liquid water, it changes to water vapor. But 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 either 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're done. Again, this is an example of a physical change. 

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2) Mixtures:
Mixtures have heterogeneous composition of matter. Each component in a mixture retain its individual properties. These components can be separated easily by physical or chemical means.
In a mixture two or more substances combine together physically but not chemically. Mixtures can either be homogeneous or heterogeneous. Homogeneous mixture has uniform composition, for e.g., glucose solution. On the contrary, in heterogeous mixtures two or more phases are present and each component can be seen easily. A salad of tomatoes, lettuce, carrots and other vegetables is a good example of heterogenous mixture.

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1)	Pure substances: A pure substance has the homogeneous composition and consistent properties throughout the sample. For e.g., sugar, table salt, water etc. These substances can not be separated into other forms by physical processes such as distillation, filtration, and evaporation. An element is a pure substance as it is made up of a particular type of atoms and can not be broken down into some other element. A pure compound is the substance that is constituted by the specific set of molecules. The molecule is the smallest stable part of a compound. For instance, on heating water gets converted into vapor but still its components (hydrogen and oxygen) remain attach to each other in the form of water molecule. 

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1)	Pure substances: A pure substance has the homogeneous composition and consistent properties throughout the sample. For e.g., sugar, table salt, water etc. These substances can not be separated into other forms by physical processes such as distillation, filtration, and evaporation. An element is a pure substance as it is made up of a particular type of atoms and can not be broken down into some other element. A pure compound is the substance that is constituted by the specific set of molecules. The molecule is the smallest stable part of a compound. For instance, on heating water gets converted into vapor but still its components (hydrogen and oxygen) remain attach to each other in the form of water molecule. 