You would have observed changing states of matter when ice cubes melt from solid into liquid water or when water boils into vapour, but have you wondered why substances change form? Changing states of matter occur when matter loses or absorbs energy. When a substance absorbs energy the atoms and molecules move more rapidly and this increased kinetic energy pushes particles far enough, that they change form. This energy is usually heat or thermal energy. In this article, let us understand the science behind the changing states of matter.
You might want to read the following articles for a deeper understanding of the topic.
What are Changes of State?
A change of state is a physical change in a matter. They are reversible changes and do not involve any changes in the chemical makeup of the matter. Common changes of the state include melting, freezing, sublimation, deposition, condensation, and vaporization. These changes are shown in the figure given below.
Why do Phase Changes Occur?
When temperature or pressure change of a system occurs, phase changes occur. When the temperature or pressure increases, the interaction between the molecules increases. Similarly, when the temperature decreases, it is easier for molecules and atoms to settle into a more rigid structure.
Changes Between Liquids and Solids
How would you make ice cubes in a tray? First, you would fill the tray with water from a tap. Then you would place the tray in the freezer compartment of a refrigerator. The freezer is very cold. What happens next?
Heat transfer occurs between the warmer tray and the colder air in the freezer. The warm water loses heat to the cold air in the freezer. This heat transfer occurs until no energy is available for the particles to slide past each other. This forces them to remain in fixed positions, locked in place by the force of attraction between them. This way liquid water is changed into solid ice. The process of liquid water changing to solid ice is termed as freezing. The temperature at which it occurs is known as freezing point.
If you took out the ice cubes from the freezer and placed them in a warm room, the ice would absorb energy from the warmer air around them. This absorbed energy would facilitate them to overcome the force of attraction holding them together, enabling them to slip out of the fixed position that they held as ice. The process in which a solids change to a liquid is called melting. The melting point is the temperature at which a solids change to a liquid.
Five Changes of State
|The process by which a substance changes from the solid phase to the liquid phase is known as melting.||The process by which a substance changes from the liquid phase to the solid phase is known as freezing.||The process by which a substance changes from the liquid phase to the gaseous phase is known as evaporation.||The process by which a substance changes from the gaseous phase to the liquid phase is known as evaporation.||
The transition of the gaseous phase to the solid phase without passing the intermediate liquid phase is known as sublimation.
It will interest you to know that every object in existence undergoes a state change. It is only a question of the amount of heat supplied to the substance. If you supply enough heat, everything on this planet can be made to change its state. The thing is though not every substance has to follow the solid-liquid-gas path. Some substances can naturally change from their solid-state to their gaseous state without entering the liquid state. This phenomenon is known as Sublimation. Examples of sublimation are, the element Iodine, Dry ice (solid CO2) and high-quality coal which at high-temperature burns and sublimates into vapour.
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Q1. When solids reach their melting point, what do they become?
Ans: Solids tranform into liquid when they reach their melting point.
Q2. What is the boiling point?
Ans: Boiling point is defined as a temperature at which a pure liquid changes into a gas.
Q3. What is the melting point?
Ans: The melting point is defined as the temperature at which the solid starts to melt.
Q4. What is the process in which solids directly transform into a gas?
Ans: Sublimation is defined as the process in which the solid-state changes to a gaseous state without changing into a liquid state.
Q5. What is evaporation?
Ans: When the liquid gets converted to gas at all the temperatures, it is known as evaporation.
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