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Physical and Chemical Properties of Matter
The characteristics that enable us to distinguish one substance from another are called properties.
Physical Properties of Matter
A physical property…
Characteristics that help us to distinguish one type of matter from another are referred to as properties. Matter exhibits two types of properties: physical and chemical.
Physical properties of matter can be measured and observed without changing the composition or identity of the matter. Odor, taste, color, appearance, hardness, density, melting and boiling points, and electrical conductivity, are all examples of physical properties.
Some of these physical properties can be observed without changing the physical state of the matter. So, when we say that helium gas is lighter than air, we are referring to a physical property. Similarly, the smell of gasoline is also a physical property.
Other physical properties can only be observed when matter undergoes physical changes. For example, pure gold in its solid-state is made up of tightly packed gold atoms. But when it is melted at a high temperature, it changes its state from a solid to a liquid. However, this liquid is still composed of gold atoms, so this is a physical change.
Similarly, when liquid water freezes to solid ice, the chemical composition of both the water and ice remains the same. Thus, physical changes only alter the state of the matter or physical conditions, without changing the chemical composition.
Crushing, grinding, slicing, blending, magnetizing, or demagnetizing are other common ways to change the physical condition of matter.
Chemical properties of matter, on the other hand, are characteristics that can only be measured and observed when the substance has a change in chemical composition. Corrosiveness, flammability, toxicity, acidity, or chemical reactivity are all examples of chemical properties of matter.
In order to identify a chemical property, we look for a chemical change. Chemical changes involve chemical reactions and are often observed through a change in color or odor.
For example, when a copper penny is exposed to air and water there is a chemical change. The copper undergoes a series of chemical reactions, one of which is shown here, to form a layer of blue-green patina on an otherwise naturally brown penny.
Thus, chemical changes produce entirely new forms of matter which differ from the matter present before the change. For instance, the flammability of gasoline is a chemical property evident from the chemical changes in the composition of gasoline when it burns, turning gasoline into entirely new substances, primarily carbon dioxide and water.
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Q1: What is the difference between physical and chemical properties of matter?
Physical properties can be measured and observed without changing matter's chemical composition, such as color, density, and melting point. Chemical properties describe how matter changes into new substances through chemical reactions, like flammability or corrosiveness. Physical properties remain the same during physical changes, while chemical properties only appear when chemical changes occur.
Q2: What happens to matter during a physical change?
During a physical change, matter alters its state or form but retains its chemical composition. Examples include melting gold, freezing water into ice, or grinding solids into powder. The substance remains chemically identical even though its appearance or physical state changes. Magnetizing, demagnetizing, and dissolving are also physical changes.
Q3: How do you identify a chemical change in matter?
Chemical changes produce entirely new forms of matter with different chemical composition than the original substance. You can identify them by observing color changes, odor changes, or the formation of new substances. For example, copper exposed to air and water forms blue-green patina, and burning gasoline produces carbon dioxide and water—both are chemical changes.
Q4: What are examples of physical properties that can be observed without changing matter's state?
Physical properties observable without state change include color, odor, density, and electrical conductivity. For instance, helium gas is lighter than air, and gasoline has a distinctive smell. These properties can be measured directly without altering the matter's physical or chemical composition. Understanding these properties is essential for measurement accuracy and precision when characterizing substances.
Q5: Why is flammability considered a chemical property rather than a physical property?
Flammability is a chemical property because it describes how matter behaves during a chemical reaction—specifically combustion. When gasoline burns, it undergoes chemical changes that transform it into entirely new substances like carbon dioxide and water. The chemical composition changes fundamentally, which is why flammability can only be observed through chemical change.
Q6: What physical properties can only be observed when matter undergoes a physical change?
Some physical properties like melting point and boiling point can only be observed when matter changes state. For example, pure gold's melting point is only observable when solid gold is heated until it becomes liquid. Similarly, water's freezing point is observed when liquid water transitions to solid ice, though the chemical composition remains unchanged.
Q7: How do chemical properties like toxicity and reactivity differ from physical properties?
Chemical properties describe how substances interact and transform through chemical reactions, while physical properties describe observable characteristics without composition change. Toxicity and reactivity only manifest when matter undergoes chemical changes. For instance, neon is unreactive because it doesn't combine with other elements, while nitroglycerin is toxic because it explodes easily through chemical decomposition.