1.4.1. EFFECT OF CHANGE OF TEMPERATURE

•Take about 150 g of ice in a beaker and suspend a laboratory thermometer so that its bulb is in contact with the ice. Start heating the beaker on a low flame. Note the temperature when the ice starts melting. Note the temperature when all the ice has converted into water.

This activity involves heating a beaker containing ice while closely monitoring the temperature using a thermometer. As the heat is applied, the temperature of the ice will remain constant until it starts melting at its melting point (0°C or 273.15 K). Initially, ice absorbs heat without a temperature change because that energy is used to break the bonds holding the ice particles in a solid structure, allowing them to transition into water.

Think of an ice cube left out on a counter. When you first take it out of the freezer, its temperature doesn’t change at first; it stays at 0°C until it melts completely. The heat from the room is absorbed to enable that melting without a noticeable change in temperature, similar to how a sponge soaks up water.

On increasing the temperature of solids, the kinetic energy of the particles increases. The energy supplied by heat overcomes the forces of attraction between the particles. The minimum temperature at which a solid melts to become a liquid at atmospheric pressure is called its melting point. The melting point of ice is 273.15 K. The process of melting is also known as fusion.

When the temperature of a solid increases, its particles move faster and gain kinetic energy. This increased motion helps the particles break free from the attractive forces binding them together in a solid structure. The melting point is a specific temperature where this transition from solid to liquid occurs. For ice, this is precisely 0°C or 273.15 K, indicating a significant event where solid ice turns into liquid water.

You might have noticed during a hot day that a block of ice melts quickly in a drink. The warmer air transfers heat to the ice (increasing particle motion), allowing it to transition into water, which enhances your beverage's chill.

The heat energy that is absorbed by ice without showing any rise in temperature is known as the latent heat, specifically the latent heat of fusion when changing from solid to liquid. The latent heat of vaporization is similarly defined for liquids turning into gases. The boiling point of water is 373 K (100°C).

Latent heat refers to the heat energy absorbed or released by a substance during a phase change without a change in temperature. For instance, when ice melts, it absorbs heat energy, but the temperature doesn’t increase until all ice has fully transitioned into liquid water. This concept applies to boiling: water absorbs heat to become steam without its temperature rising during the phase change. The boiling point is the temperature at which this transition occurs, such as water boiling at 100°C or 373 K.

Consider cooking pasta. When you boil water, the temperature remains the same at the boiling point as steam begins to form—meaning all energy goes into turning water into vapour instead of increasing temperature, so your pasta cooks at a constant temperature.

Some substances change directly from solid to gaseous state, a process known as sublimation, such as camphor or dry ice. The reverse process where a gas changes to solid is called deposition.

Sublimation occurs when a solid changes directly into a gas without passing through a liquid state. A notable example is dry ice, which directly transitions from solid to carbon dioxide gas when pressure is reduced. In reverse, deposition describes gas transforming back into a solid. These processes illustrate the versatility of matter regarding phase changes and the influence of temperature and pressure.

Think of the phenomenon of frost forming on a cold surface during winter. Water vapor from the air can turn directly into solid ice on colder surfaces without becoming liquid first—this is deposition. Similarly, your scented candle might leave a faint scent trail as the wax sublimates into gas when lit, filling the room with its aroma.

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