Intensive density, more accurately referred to as density being an intensive property, means that a substance's density remains constant regardless of the amount of the substance present.
Understanding Intensive Properties
Intensive properties are characteristics of a substance that do not depend on the amount of matter being considered. Think of it this way: if you have a small sample of pure gold and a large ingot of pure gold, both will have the same density, color, and melting point. These are all intensive properties.
Other examples of intensive properties include:
- Temperature: A cup of coffee and a pot of coffee at the same temperature will both read the same on a thermometer.
- Color: A drop of blue dye and a gallon of the same blue dye will both be the same color blue.
- Melting Point: A gram of ice and a kilogram of ice both melt at 0°C (at standard pressure).
- Boiling Point: Water boils at 100°C, whether you're boiling a thimbleful or a swimming pool (again, at standard pressure).
Why Density is Intensive
Density is defined as mass per unit volume (typically expressed as g/cm3 or kg/m3). If you double the amount of a substance, you double both its mass and its volume. Since density is a ratio of mass to volume, the ratio remains the same, regardless of the amount of substance.
For example, consider water:
| Mass (g) | Volume (mL) | Density (g/mL) |
|---|---|---|
| 10 | 10 | 1.0 |
| 100 | 100 | 1.0 |
| 1000 | 1000 | 1.0 |
As you can see, even though the mass and volume change, the density of water remains constant at 1.0 g/mL.
Contrast with Extensive Properties
It's helpful to contrast intensive properties with extensive properties. Extensive properties do depend on the amount of matter present. Examples include:
- Mass: More material means more mass.
- Volume: More material occupies more space.
- Length: A longer piece of string has a greater length.
- Energy: It takes more energy to heat a large pot of water than a small cup.
Summary
Density is an intensive property because its value is independent of the amount of the substance. This makes density a useful characteristic for identifying materials, as it provides a consistent value regardless of the sample size.
