Have you ever wondered why ice melts when you heat it, or why water boils when you heat it more? Or why steam condenses when you cool it down? These are examples of physical changes of substances, which are changes in their form or state without changing their chemical composition. In this article, we will explore how temperature is related to the physical change of a substance, and what happens at the molecular level when a substance changes its state.
Contents
What is a Physical Change?
A physical change is a change in the appearance or state of a substance, but not in its chemical identity. For example, when you cut a piece of paper into smaller pieces, you are changing its shape and size, but not its chemical composition. It is still paper, made of cellulose molecules. A physical change can also involve a change in the state of matter, such as solid, liquid, or gas. For example, when you melt ice into water, or boil water into steam, you are changing its state, but not its chemical composition. It is still water, made of H2O molecules.
What is Temperature?
Temperature is a measure of the average kinetic energy of the particles in a substance. Kinetic energy is the energy of motion, and particles are the atoms or molecules that make up a substance. The higher the temperature, the faster the particles move and collide with each other. The lower the temperature, the slower the particles move and collide with each other.
How is Temperature Related to the Physical Change of a Substance?
Temperature is related to the physical change of a substance because it affects the energy and arrangement of the particles in a substance. As temperature increases, the particles gain energy and move faster and farther apart from each other. As temperature decreases, the particles lose energy and move slower and closer to each other.
The energy and arrangement of the particles determine the state of matter of a substance. In general, solids have low energy and high order, liquids have moderate energy and moderate order, and gases have high energy and low order. Figure 1 shows how the particles are arranged in different states of matter.
Figure 1: Particle arrangement in different states of matter (according to BBC)
When a substance changes its state due to a change in temperature, it undergoes a phase transition. A phase transition is a type of physical change that involves a change in the organization or structure of a substance. There are six common types of phase transitions:
– Melting: solid to liquid
– Freezing: liquid to solid
– Vaporization: liquid to gas
– Condensation: gas to liquid
– Sublimation: solid to gas
Deposition: gas to solid
Each phase transition has a specific temperature at which it occurs for a given substance under normal pressure. This temperature is called the phase transition point or equilibrium point. For example, water has a melting point of 0°C and a boiling point of 100°C under normal pressure.
During a phase transition, the temperature of a substance does not change until all of it has changed its state. This is because the energy added or removed during a phase transition is used to overcome or release the intermolecular forces that hold the particles together or apart. Intermolecular forces are the attractive or repulsive forces between molecules that determine their physical properties.
The amount of energy needed to change the state of one gram or one mole of a substance is called the latent heat or enthalpy of phase transition. The latent heat depends on the type and strength of intermolecular forces in a substance. For example, water has a high latent heat of vaporization because it has strong hydrogen bonds between its molecules that require a lot of energy to break.
Conclusion
In summary, temperature is related to the physical change of a substance because it affects the energy and arrangement of the particles in a substance. A change in temperature can cause a change in the state of matter of a substance if it reaches its phase transition point. A phase transition involves a change in the organization or structure of a substance due to overcoming or releasing intermolecular forces. The amount of energy needed or released during a phase transition is called the latent heat or enthalpy of phase transition.
