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Hey kids, did you know matter can change from one state to another and vice versa? That means, if an element is in the solid state, it can be converted into the liquid state and further into the gaseous state. Similarly, a gas can be converted into a liquid and even into a solid. Yes, it can be! Read on to find out how-
The state of matter refers to its physical state. All matter can move from one state to another. This is known as interconversion of the states of matter. Matter can change from one state to another when specific physical conditions change– i.e. temperature and pressure of the substance. How this conversion takes place can be understood by the molecular theory of change of states.
Molecular Theory Of Change Of States
When a certain compound or element is heated, the temperature of the substance rises. The molecules in the substance start vibrating faster, in response to the heat energy they receive. As the substance is continually supplied with heat energy, the intermolecular spaces between the molecules increase, finally reaching a point when the solid is converted into a free-flowing liquid. Further application of heat energy causes the molecules to vibrate faster and move further away from each other, resulting in the liquid converting into its gaseous form.
Change Of State In Water-
Think about it this way. Let’s say you have a large cube of ice. When this ice cube is supplied with heat energy, its temperature goes up; the molecules get more excited and bounce around a lot more. Intermolecular spaces between molecules increase, finally causing the ice cube to convert into liquid water. If you give a liquid water molecule enough energy, it escapes the liquid state and becomes a gas i.e. water vapour.
Conversely, if you cool the water vapour, its intermolecular spaces between molecules decrease and it condenses to form water droplets, i.e. it converts from the gaseous state to the liquid state. When this water is cooled further, the intermolecular spaces between molecules decrease even more, and the water finally converts into ice i.e. it changes from the liquid state to the solid state.
The Role Of Temperature And Pressure In Change Of State-
Most times, a substance doesn’t want to change states. Scientists have to use all of their tricks to make it change its state. They may have to increase or decrease its temperature by a huge amount, or they may have to apply a tremendous amount of pressure on the substance, causing it to finally change into the desired state.
For example, Iron must be heated to 1535°C in order to convert it into liquid iron. Solid gold converts into liquid at a temperature of 1064°C. A gas is converted to liquid or solid by applying pressure and reducing its temperature by huge amounts. Nitrogen gas has to be cooled to the temperatures of -210°C to -196°C before it converts into liquid nitrogen. When cooled further to below -210°C, nitrogen freezes and becomes a solid. Isn’t that interesting?
Sublimation-
Not all elements display the solid to liquid-liquid to gas conversion. Sometimes, a solid, on heating, directly changes into gas without changing into liquid. The resultant gas, on cooling, changes back to solid without changing into liquid. This process is called sublimation. Only certain elements exhibit the property of sublimation. For example, solid ammonium chloride, on heating, directly converts into vapour without changing to the liquid state. These vapours get condensed to the solid state when cooled. Camphor and naphthalene are other common substances that sublime.
