All substances have distinct physical and chemical properties, and may undergo physical or chemical changes. Physical properties, such as hardness and boiling point, and physical changes, such as melting or freezing, do not involve a change in the composition of matter.
Chemical properties, such flammability and acidity, and chemical changes, such as rusting, involve production of matter that differs from that present beforehand. Measurable properties fall into one of two categories. Extensive properties depend on the amount of matter present, for example, the mass of gold. Intensive properties do not depend on the amount of matter present, for example, the density of gold. Heat is an example of an extensive property, and temperature is an example of an intensive property.
Austin State University with contributing authors. Learning Objectives Describe the difference between physical and chemical properties or changed. Identify a property or transformation as either physical or chemical using symbolic, particulate, or macroscopic representations. Identify the properties of matter as extensive or intensive. Recognize and describe the parts of the NFPA hazard diamond. 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. Noticeable Odor When two or more compounds or elements are mixed and a scent or odor is present, a chemical reaction has taken place. Spoiled Egg. Formation of a Precipitate The formation of a precipitate may be one of the most common signs of a chemical reaction taking place.
Formation of Bubbles The formation of bubbles , or rather a gas , is another indicator of a chemical reaction taking place. Gas Formation However, most reactions are much more subtle. References Chang, Raymond. General Chemistry: the Essential Concepts. Chemistry for Dummies. For Dummies, Petrucci, Ralph H. General Chemistry Principles and Modern Applications. Problems 1. Which of the following is a chemical reaction?
Freezing liquid Mercury Adding yellow to blue to make green Cutting a piece of paper into two pieces Dropping a sliced orange into a vat of Sodium Hydroxide Filling a balloon with natural air 2. Which of the following is a physical reaction? Boundless vets and curates high-quality, openly licensed content from around the Internet.
This particular resource used the following sources:. Skip to main content. Introduction to Chemistry. Search for:. Physical and Chemical Changes to Matter. Learning Objective Identify the key features of physical and chemical changes. Key Points Physical changes only change the appearance of a substance, not its chemical composition. What Is a Physical Change? In a physical change, the material involved in the change is structurally the same before and after the change.
Types of some physical changes are texture, shape, temperature, and a change in the state of matter. A change in the texture of a substance is a change in the way it feels. For instance, a block of wood may feel rough when you run your finger across it but rubbing the wood with sandpaper smooths the surface so it no longer feels rough.
The wood itself has not changed during sanding to become a new material, only the texture of the surface changed. A piece of metal may be heated in a fire until it glows, but the metal is the same material before heating and after cooling.
Similarly, when a material changes phase, it only changes physically; the substance is still the same. Think about ice melting into water, and then water being heated up and turning into steam. The chemical structure of water is the same whether it is a solid ice , liquid, or gas steam. What Is a Chemical Change? A chemical change occurs when the composition of a substance is changed, which requires the breaking and forming of chemical bonds during a chemical reaction.
This results in the rearranging of atoms in substances to form the products of a chemical reaction, which are brand new molecules that cannot be easily reverted back to their original state.
Sometimes it is difficult to tell if a chemical reaction has taken place. To help determine whether there has been a reaction, chemists consider the basic indicators that a reaction has occurred, such as a change in temperature, a change in color, the development of an odor, the formation of a precipitate , or the formation of a gas.
In a chemical alteration, the temperature change occurs as a result of the breaking or formation of chemical bonds. When the chemical bonds of the reactants are broken, sometimes excess energy is released, causing heat to be discharged, and leading to an increase in temperature. Alternatively, a reaction may require energy from the environment in order to take place, causing heat to be absorbed, and leading to a decrease in temperature.
Burning wood is an example of a reaction that releases excess energy as heat. A chemical cold pack in a first aid kit is an example of a chemical reaction that absorbs heat energy resulting in cooling. An example of a color change signaling a chemical reaction can be observed when iron reacts with oxygen to produce iron oxide, such as when an iron nail is left outside, and it develops a reddish-brown rust.
0コメント