Change of State – Latent Heat

There are different types of changes of states happening in our day-to-day life which we notice in our surroundings. Different forms of state can be solid-state, liquid state, or gaseous state. Materials can exist in either of the forms and they can change between their states. When they change, properties of the substances will also change—that shouldn’t be too surprising for us. However, if the state changes are reversed the substances will recover the properties they had to begin with. 

Solid-state

As its name suggests, “solid” describes a condition of matter in which the component particles are tightly packed together. Atoms, volume, ions, and other component particles may be found in a solid. The form, mass, and volume of solid things may be attributed to the strong and brief interactions between their constituent particles.

Whenever material is heated, it absorbs energy and heat. Then the particles rearrange because the attractive forces can no longer hold them tightly. 

Liquid state 

The same happens when liquid is heated the attractive forces between the molecules break leading them to become more widely dispersed and a gas to form. A liquid is a fluid that cannot be compressed in a container, they have a standard volume irrespective of pressure change. Volume is always specific if the temperature and pressure doesn’t change

Boiling: Liquid to Gas

Boiling point: Temperature at which a liquid boils and changes rapidly into a gas at atmospheric pressure

Gaseous state

A gas can be compressed in any form of container, it will make sure that the container is fully occupied with the matter of gas when it is suppressed in it. Gas filled in any form of a container has no precise volume or shape. Liquid can be converted to a gas when heated at constant pressure or by lowering the pressure at standard temperature.

Four words describe changes in state

• Freezing

• Melting

• Evaporating

• Condensing

Think of the boiling pan of water, we notice all of the water bubbles. This is because all the particles have enough energy to become gaseous but water standing in the pan that is not being heated up by anything other than the environment can also return to a gaseous state. This is called Evaporation. All the particles at the surface of the energy have to change from liquid to gas hence evaporation is a slower process than boiling even though achieves a slower state change both are types of vaporisation. The opposite of this vaporisation is condensation, the transition from gas to a liquid. For example, think of a cold canned soda on a sunny weather day, those water droplets on the outside, or the dew grass in the morning, or a steamed up mirror after a hot bath even the clouds in the sky or a foggy windshield in the car these are examples of condensation.

Let’s consider a transition between solids to liquid states

Melting and Freezing

Melting: Solid to Liquid

Melting point: The temperature when solid starts melting  and changes into a liquid state at atmospheric pressure (Heat energy is used to overcome the strong forces of attraction)

Think of the arctic sea ice, in the summer when air temperatures are warmer more heat energy is observed by ice. This causes bonds to break between ice and water molecules and then ice starts to melt in this situation solid ice becomes liquid water but in the winter air temperatures are cooler seawater freezes and ice starts forming again in the water. There is less heat energy within the ice and holding it together to form more ice. There are some situations where a solid-state transfers directly to a gaseous state. This process is called sublimation, this can be demonstrated by particular materials such as solid carbon dioxide also known as dry ice when subjected to certain pressure it will turn state change directly to gaseous carbon dioxide. Liquid carbon dioxide does exist but only because under high pressure a similarly gaseous state can turn to a solid-state when cooled this is called deposition.

Latent heat

Latent heat is used to overcome the force of attraction, when we are heating it increases the kinetic energy of the molecules but when we reach the saturation point all that heat is helpful to overcome the force of attraction, then the change of state happens. In the point of latent heat kinetic energy does not increase, all this heat is used to overcome the force of attraction in other words latent means hidden. It is all hidden in the substance.

Latent stands for hidden because this heat is not getting manifested externally as rise in temperature. We call this heat a latent heat or hidden heat. There was a change of state from ice to water or from water to vapour the heat energy that was observed was not completely manifested. A similar thing will happen if water freezes into ice or water condenses into water the heat that will be liberated will not be externally manifested as any rise or fall in temperature

Conclusion

In conclusion, any substance is present in a certain form and its matter can be changed to any particular state based on a process like discussed above. Water can be expressed in three states: when water is in solid-state it is called ice and when the same water is at room temperature it is called liquid state and when you boil the water with high-temperature water evaporates and this steam is called gaseous state. 

The steps followed are: Ice is getting heat energy -> the kinetic energy of the particles of ice increases -> speed of the particles increases -> interparticle space of the ice increases -> interparticle attraction force decreases -> ice converts into water.