Matter is everything that surrounds us. Intensive and extensive properties refers to the classification of properties according to their dependence on the amount of matter . Let’s look at each one separately.
Defining intensive properties
Are those properties that do not depend on the quantity or size of the material . They are also known as intrinsic or local properties.
Suppose we have a system with a property X. If we divide the system into parts A, B, and C, the property X of A equals the property X of B and C:
Key to remember if a property is intensive : the property of the parts is equal to the property of the system.
Examples of intensive properties
Here are some of the best-known intensive properties.
The temperature is measured with a thermometer.
Temperature is the measure of the average kinetic energy of atoms. The Celsius scale, or centigrade, is the most widely used scale worldwide to measure temperature.
It is an intensive property because if we measure the temperature of a liter of water or a glass of water under the same conditions, the measurement will be the same.
- Melting point
The melting point is the temperature at which a solid phase compound enters its liquid phase. In the international system the unit is the kelvin (K). It can also be expressed in degrees centigrade.
It is an intensive property because it does not depend on the amount of material. The temperature at which one gram of a substance melts will be equal to the temperature at which one kilogram of the same substance melts. For example, gold has a melting point of 1,064ºC; so 1 gram of gold or a gold bar must reach the temperature of 1,064ºC to go from the solid to the liquid state.
- Boiling point
The boiling point is the temperature at which a liquid phase compound passes into its gas phase. The typical example is that of water, which boils and turns into steam at 100ºC when the atmospheric pressure is equal to 1 atmosphere.
For example, distillation is a technique that takes advantage of the difference in the boiling points of the compounds to be able to separate them, as in the case of alcohol and water.
The elasticity of each spring is independent of its size.
Elasticity is a measure of how much an object can deform when a certain force is applied to it. Materials like rubber have a greater elastic property.
It is an intensive property because a meter of rubber has the same elasticity as 10 centimeters of rubber.
Density is the ratio of the mass of a body or material to the volume it occupies. It is calculated by dividing the amount of mass in grams by the volume in milliliters.
It is an intensive property because the density does not vary either if we measure it in one kilogram of matter, or in two tons of it.
Viscosity is the property of fluids to resist flow. The more viscous a fluid is, the thicker it will be. Fluid viscosity generally decreases with increasing temperature.
Viscosity is measured in newtons-seconds per square meter (Ns / m 2 ). Another commonly used unit for viscosity is the poise (P), where 10 P equals 1 Ns / m 2
The viscosity of honey at a certain temperature is the same regardless of its quantity.
- Surface tension
Thanks to the surface tension, some insects can move about in the water.
Surface tension is the property of liquids to resist the forces applied to their surface. This property is the result of the forces that hold the liquid molecules together on the surface.
It is an intensive property because the intermolecular forces are equal on the entire surface of the fluid.
- Specific heat
The high specific heat of the water allows to dissipate the heat generated in the motors.
Specific heat is an intensive property that describes how much heat is needed to increase the temperature of a unit of mass of a material. In the international system the specific heat unit is Joules per kilogram centigrade (J / kg ºC).
The specific heat of water (4186 J / kg ºC) is five times greater than that of glass (840 J / kg ºC). This means that five times more heat is required to increase the temperature of a kilo of water than a kilo of glass.
Copper has a very low resistivity, so it conducts electricity easily.
Resistivity is the property of a material to resist the flow of electrical charges, regardless of its size or shape. In the international system the unit for resistivity is ohm meter (Ω · m)
- Thermal conductivity
Thermal conductivity is the ability of materials to transfer heat. In the international system of units it is measured in watts per meter and kelvin (W / mk)
Defining extensive properties
Are those properties that depend on the size of the system . In this case, if we divide a system into parts A, B and C, then the property of the system will be equal to or greater than the sum of the parts:
Key to remember if a property is extensive: the property of the parts is added to the property of the system.
The ratio or quotient of two extensive properties is transformed into an intensive property. For example, density is the division of two extensive properties: mass and volume.
Example of extensive properties
Below are some extensive properties.
The length depends on the distance to be measured.
Length is a physical measure of distance: the separation between two objects, the space that an object moves, the length of a cable, and other measures depend on the distance. The unit of the international system for length is the meter.
It is an extensive property because it depends on the size: if we cut a ten-meter rope into one-meter pieces, the length of the final pieces is not the same as the original.
The mass depends on the amount of material.
Mass is the amount of matter that an object contains. Mass, unlike weight, does not depend on gravity. The unit of the international system for mass is the kilogram.
It is an extensive property because when you remove a piece of the material being measured, the final measurement of mass changes.
Volume is the measure of the three-dimensional space an object occupies. In the international system the unit of volume is the cubic meter (m 3 ). The liter is also used. The volume of a solid can be measured by the volume of liquid it can displace when it is completely submerged.
It is an extensive property because adding more material to a container changes the volume, even if it is the same material.
- Number of molecules
The number of molecules that make up the air varies according to the space they occupy.
The number of molecules in a material varies depending on the amount of the material. We know that one mole of a substance has 602,000,000,000,000,000,000,000 molecules, in scientific notation it would be 6.02×10 23 , this number is also known as the Avogadro number .
It is an extensive property because the number of molecules increases or decreases depending on whether there is more or less material.
Inertia is the property of bodies to resist changes in motion or rest . It is a property associated with mass, the more mass, the more inertia.
It is an extensive property because it depends on the amount of material, the inertia of a toy car is less than the inertia of a car.
For example, if we place some books on a chair with casters and push it against a wall, the books inertia continue their movement when it hits the wall.
- Heat capacity
Heating a small kettle requires less heat than a large kettle.
Heat capacity is the amount of heat required to change the temperature of a substance . In the international system the unit of heat capacity is joules per kelvin (J / K).
It is an extensive property, since it depends on the amount of substance, in addition to temperature and pressure. To heat 10 liters of water requires more heat than to heat a cup of water.
Enthalpy is the amount of energy that a system transfers or absorbs from its surroundings . In the international system the enthalpy unit is joules (J).
For example, Rubidium’s reaction with water releases a large amount of heat.
Entropy is the measure of the disorder of a system . In the international system the unit of entropy is joules per kelvin (J / K).
It is an extensive property because the larger the system, the greater the disorder. The trend in nature is disorder.
- Electric charge
Static electricity occurs when there is excess electrical charge on the surface of an object.
Electric charge is a property that produces forces that can attract or repel matter . In the international system the unit of charge is the Coulomb (C), which represents 6.242×10 18 e , where e is the charge of the proton. The charge can be positive or negative.
Resistance is the electrical property that prevents the passage of current . In the international system the resistance unit is measured in Ohm. The resistance of an object depends on its shape and length.