1. Physical & Chemical Change & Properties
Understanding how to differentiate between physical and chemical changes will help you better understand the transformations of matter you observe.
Chemistry 4(A)

2. Physical Properties
Physical property – property that can be measured or detected without changing the chemical composition of the object
Examples of physical properties include
Appearance
Odor
Hardness
Mass
Volume
Density
Melting point
Boiling point
Substance
State
Color
Melting Point (°C)
Boiling Point (°C)
Density (g/mL)
Chlorine
Gas
Greenish-yellow
-101
-34
0.0032
Water
Liquid
Colorless
100
1.00
Sodium chloride
Solid
White
801
1413
2.17
A physical property is a property that can be measured or detected without changing the chemical composition of an object. Some examples of physical properties include: appearance, odor, hardness, mass, volume, density, and melting and boiling points. However, there are many other observable characteristics that fall under this category. Scientists often use physical property information to identify a substance, because no two substances have exactly the same physical property information. The table shows the physical properties of a some substances. You can see that the difference in these physical properties could be used to distinguish these substances from one another.

3. 2K(s)+ 2H2O(l)  2KOH (aq) + H2(g)
Chemical Properties
Chemical Property – ability of a substance to undergo a change that transforms it into one or more new substances
Ex) Ability of group 1A metals to react with water forming a base and hydrogen gas
2K(s)+ 2H2O(l)  2KOH (aq) + H2(g)
By Ozone aurora (Own work) [CC-BY-SA-3.0]
Chemical properties describe the ability of a substance to undergo a change that transforms it into one or more new substances.
For example, a chemical property of group 1A metals is the ability of these metals to react with water forming a base and hydrogen gas.

4. Ex) Physical & chemical properties of bromine
Physical vs. Chemical Properties
Ex) Physical & chemical properties of bromine
Physical Properties
Orange-brown color
Fuming liquid
Boiling point = 58∘C
Chemical Properties
Ability to corrode tissue upon contact
Ability to react with metals to form salts
Ability to react with hydrogen ions in aqueous solutions to form hydrobromic acid
By Alchemist-hp (pse-mendelejew.de) (Own work) [FAL or CC-BY-SA-3.0–de]
Let’s practice distinguishing the physical properties from the chemical properties of a substance. For example, let’s determine some of the chemical and physical properties of the element bromine. Some physical properties of bromine include its orange–brown color, its state as a fuming liquid, and its boiling point at 58∘C. Some of its chemical properties include its ability to corrode tissue upon contact, react with metals to form salts, and react with hydrogen ions in aqueous solutions to form hydrobromic acid.

5. Ex) Sublimation of iodine
Physical Change
Physical change – transformation that does not change the chemical composition of the material
Change of state
Melting
Freezing
Vaporization
Condensation
Deposition
Sublimation
Change in position
Ex) Sublimation of iodine
Ex) Erosion
A physical change is a transformation that does not change the chemical composition of the material.
Changes of state are some of the most common physical changes and include the following: melting, freezing, vaporization, condensation, deposition, and sublimation. For example, the sublimation of iodine is a physical change. Although the state of iodine is changing from solid to gas, the chemical composition of the iodine does not change.
Another common type of physical change is the change in position of a material. You can alter the position of materials, moving or breaking them up, without changing their chemical composition. An example of this type of change in nature is erosion. Erosion is the change in position of rocks and soil due to the movement of water. Though the soil has been moved, its chemical make up has not changed.

6. Chemical Change
Chemical change – transformation of a substance into at least one new substance
Also known as a chemical reaction
Ex) Reaction of cobalt(II) nitrate and sodium hydroxide
By Capaccio (Own work) [CC-BY-SA-3.0 ]
Unlike a physical change, a chemical change is the transformation of a substance into at least one new substance. A chemical change is also known as a chemical reaction.
For example, a chemical change occurs when a sodium hydroxide solution (the clear liquid) is added to a cobalt(II) nitrate solution (the brown liquid). The result of the reaction is the formation of two new substances, sodium nitrate and cobalt(II) hydroxide. The new substances have different properties than the original substances. For example, unlike the original substances, one of the products, colbalt(II) hydroxide, is a blue solid. In this reaction, the visible change in the physical properties of color and state of matter make it easy to recognize that a least one new substance has been formed and thus a chemical change has occurred.
Co(NO3)2(aq) + 2NaOH(aq)  2NaNO3(aq) + Co(OH)2(s)

7. Chemical Change Signs of chemical change
Light or heat is absorbed or released
Change in color or odor
Production of a gas or solid from a liquid
Precipitate – a solid that forms from a reaction between liquids
Irreversibility
I, MarcusObal [GFDL ]
Nickomargolies [GFDL ]
By Dr.T (Own work) [CC-BY-SA-3.0 ]
Since chemical reactions form new substances, the products of a chemical reaction will have different properties than the original substances. These changes in properties are signs that chemical changes have occurred. Typically, a chemical change will exhibit several of the following signs.
Chemical change often causes light or heat, which are both forms of energy, to be absorbed or released. An example of this is the chemical change that occurs when wood is burned, giving off energy in the form of heat and light.
Another potential sign of chemical change is a change in color or odor. For example the chemical change that occurs as food rots displays both these signs. When food rots, the reaction converts the original substances in the food to new substances that have fowl odors and a brown color.
The production of a gas or solid from a liquid can also signify that a chemical change has occurred. A precipitate is a solid that forms from the reaction between liquids. An example of a chemical reaction in which a precipitate is formed is the reaction between silver nitrate solution and potassium chloride solution. When the two substances react an insoluble solid is formed and sinks to the bottom of the reaction vessel. An example of a chemical reaction that produces gas is the reaction between baking soda and vinegar.
Another sign that often accompanies chemical change is irreversibility. For example, the chemical changes that occur when food is cooked cannot be reversed. Once the food is cooked it can no longer be return to its original composition.
The presence of one of the signs listed here does not guarantee that a chemical change took place, but the presence of more than one signifies that a chemical change most likely took place.

8. Ex) Classify as either a chemical or physical change
Physical vs. Chemical Change
Ex) Classify as either a chemical or physical change
Change
Evidence
Type of Change
Candle burning
Water boiling
Baking a cake
Releases light and heat
Change in color and odor
Irreversible
Chemical
Phase change (forms no new substances)
Physical
Let’s practice classifying the following changes as either chemical or physical.
A burning candle releases energy as light and heat, exhibits changes in color and odor, and is an irreversible process so it must be a chemical change.
Boiling water exhibits some of the evidences of chemical change, however, by definition it cannot be a chemical change because no new substances are formed. Boiling only changes the phase of the water. All phase changes are physical changes.
When a cake is baked it absorbs heat, changes in color and odor, releases gases (causing the cake to rise), and is an irreversible process. Therefore, the changes that occur while a cake is baking must be chemical.
Absorbs heat
Change in color and odor
Releases gases
Irreversible
Chemical