Matter is the substance that makes up everything in the universe, defined simply as anything that has mass and takes up space. Scientists characterize matter using identifiable traits to distinguish one material from another, such as how iron differs from wood. These properties are broadly categorized into two types: physical properties, which do not alter the material’s identity, and chemical properties, which require a chemical transformation.
The Core Definition of Physical Properties
A physical property is a characteristic that can be observed or measured without changing the substance into a different kind of matter. This means the material’s chemical identity remains the same before and after the observation. For example, when ice melts into liquid water, the substance changes state but remains \(\text{H}_2\text{O}\). These properties are determined through simple observation or measurement and relate to the material’s physical state or structure. Physical properties are categorized as intensive (like color and density, independent of amount) or extensive (like mass and volume, dependent on amount).
Key Examples of Physical Properties
Physical properties encompass a wide range of traits, from those easily seen to those requiring precise measurement. Observable properties are qualitative, meaning they are descriptive and do not involve a number. These include characteristics like color, odor, texture, and luster, which is the way a material reflects light. The state of matter—solid, liquid, or gas—at a given temperature and pressure is also a key observable property.
Measurable properties are quantitative and require a tool to determine a numerical value. Density is a widely used quantitative physical property, calculated by dividing the mass of a substance by its volume (\(\rho = \text{m}/\text{V}\)). This value is constant for a pure substance at a specific temperature, regardless of the sample size. Another element is solubility, which measures the maximum amount of a substance that can dissolve in a solvent at a given temperature.
The temperature at which a substance changes state is also a quantifiable physical property. The melting point is the temperature at which a solid turns into a liquid, such as the \(0^{\circ}\text{C}\) point for water. Similarly, the boiling point is the temperature where a liquid changes to a gas. Measuring the boiling point of water converts it to steam, but the steam is still \(\text{H}_2\text{O}\), confirming that the measurement did not change its identity. Other measurable properties include electrical conductivity (the ability to transmit an electric current) and malleability (the ability of a material to be hammered into thin sheets).
How Physical Properties Differ from Chemical Properties
The fundamental distinction between physical and chemical properties lies in whether the act of observation or measurement alters the substance’s identity. Physical properties can be determined without causing a chemical change. In contrast, a chemical property describes a substance’s potential to undergo a transformation that results in a completely new material. To observe a chemical property, the substance must react and change its molecular composition.
For instance, flammability is a chemical property because confirming it requires burning the substance, which converts it into entirely different compounds like ash and carbon dioxide. Another element is reactivity, which describes a material’s tendency to combine chemically with other substances, such as iron’s ability to rust when exposed to oxygen and water. Chemical properties describe how a substance behaves in a reaction, whereas physical properties describe what the substance is like in its original state.