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Change of State

Hailstorm Hailstorm: Nature, the best deep fridge. A hailstorm is caused when hailstones are developed in the clouds. Water droplets are super-cooled causing ice crystals to grow into hailstones, which shows the change of state from water to ice. This topic deals more with different states of matter and their properties at different temperatures.

Learning objectives

After completing the topic, the student will be able to:

  • Discuss and explore how substances behave when changed into various states and relate to everyday science.
  • Investigate the process of evaporation, condensation, melting, freezing and relate their applications in daily life scenarios.
  • Explore about the concept of latent heat of a substance and distinguish from specific heat.
  • Discuss, examine and investigate about the concept of regelation and its application in daily life.
States of matter States of matter The three physical states of water are water vapor, liquid water, and ice. In this picture we see both the liquid and solid states of water. We cannot see water vapor. What we see when we look at steam or clouds is tiny droplets of liquid water dispersed in the atmosphere.

In a solid, the atoms or molecules are very tightly bound. But in a liquid the binding is not very strong. In a gaseous state the binding is even weaker.

Three states of matter

Matter can be a gas, a liquid, or a solid. These three forms of matter are called the states of matter (phases of matter). Elements and compounds can be any of these three states - solids, liquids or gases. There are other states of matter too, like the plasma state and a very recent discovery at ultra low temperatures – known as a Bose–Einstein condensate.

Matter in a solid state has a definite shape or form. It is generally defined in terms of the weight of the solid. On the other hand, matter in a liquid state has no definite shape or form. The liquid takes the form of the container in which it is placed. It may not fill the container completely but the liquid can be defined in terms of volumes of liquid. Matter in a gaseous state is neither in a definite shape or volume. It is very ephemeral. If put in a container, it fills the container completely. The container volume in which it is placed defines a gaseous state of a substance.

The properties of the states can be understood on the molecular level. In a gas the molecules are far apart and are moving at high speeds, colliding repeatedly with each other and with the walls of the container.The force of attraction between gas molecules are weak as they are very far apart from each other. In a liquid the molecules are packed more closely together, but still move rapidly, allowing them to slide over each other; thus, liquids pour easily. The force of attraction between the molecules in liquid are little stronger than that of the gas molecules. In a solid the molecules are held tightly together, usually in definite arrangements, in which the molecules can wiggle only slightly in their otherwise fixed positions. Thus, solids have rigid shapes. The force of attraction between the molecules of the solids are more stronger.

Change of State of a Substance or a Compound Change of states of a substance or a compound Melting: Solid matter changes its state to liquid.
Freezing: Liquid matter loses heat and changes its state to solid.
Boiling (vaporization): Liquid matters gain heat and change their states to gas.
Condensation: Gas molecules lose heat and change its phase to liquid.
Sublimation: Solid matter changes directly to gas.
State of Ice
Ice melts and vaporizes quickly on hot griddle Three states of H2O are Ice, water and vapor. 720 cal/gm is needed to first melt the solid, then vaporize the liquid water. The energy is absorbed by individual molecules of water to break the H bonds holding the crystal together resulting in a liquid and then a gas.
Change of states in matter

As you know, a molecule of water is made up of two hydrogen atoms and one oxygen atom. At ordinary temperatures, water is in liquid form. Take little amount of water in a container. If we heat the container to 100°C, the water inside will boil and become steam. The binding between each molecule of water is broken due to heat and therefore the distance between each molecule becomes large. Steam is the gaseous state of water. If we reduce temperature, the steam will condense to become water again. Now, if we reduce the temperature of the container to 0°C, the water will solidify into ice. Thus the three states of matter for a water molecule are ice in solid state, water in liquid state and steam in gaseous state.

It is good to remember that the states of matter depend on its temperature, the pressure that is exerted on it, and transfer of energy or heat accompanies changes of state. Matter changes form when heat is supplied or removed.

The change from solid Solid to Liquidliquid Liquid to Gasgas is called a change of state of a substance or a compound.

We know by now that solids are bound together by tight bonds. As we supply energy, the bonds start to stretch. This transforms the solid into liquid state. As more energy is given to the system, the bonds stretch even more and ultimately break. The liquid then is turned into gaseous matter. The inter–molecular forces become weaker as we go from solid to liquid to gaseous state.

The process of converting a solid into liquid is known as melting. The temperature at which melting occurs is called the melting point. The reverse of melting is called freezing or solidification. If solidification makes the solid into properly structured crystals, it is also known as crystallization process. The process of converting liquid into gas is called vaporizing. The reverse of vaporizing is known as condensation. The temperature at which the liquid turns into gas is called the boiling point of the substance.

Some solids like dry ice, iodine, frozen carbon dioxide, naphthalene balls convert to gaseous state directly from their solid state. They jump the liquid state. The process of going from solid state to gaseous state directly is known as sublimation. Reverse of sublimation is called condensation.

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