An Idea on Thermal Expansion in Liquids

The liquids have no distinct shape and take on the body of the container in which they are placed. Thus, liquids can be classified based on their volume. When the liquid in the container is heated, it causes the container to expand and hence decreases the liquid level. When the liquid is heated, it is heated above its actual temperature. Only the initial and final states can be seen; the intermediate state cannot be seen. An apparent expansion of the liquids is one such observed expansion.

When expansion happens, and the total accumulation in volume is measured, the expansion is referred to as the absolute expansion of liquids. Because liquid atoms vibrate rapidly about their fixed points, they expand. However, because the bonds between individual molecules are typically looser in liquids, they expand more than solids. This is also the underlying principle of liquid-in-glass thermometers. An increase in temperature causes the liquid to expand, causing it to rise up the glass. Liquids do not have a distinct shape of their own. The shape of a liquid is always determined by the container into which it is poured. As a result, when a liquid is heated, the volume of both the liquid and the container changes. Thus, there are two types of liquid thermal volume expansion.

Real and Apparent Cubical Expansion of liquid

Liquids have no standard structure or surface area and always take on the shape of the container in which they are stored. As a result, in the case of liquids, we are only concerned with volume changes when they are subjected to heat. The percentage of a liquid’s volume that expands per kelvin increase in temperature is known as its real or absolute expansion.

The direct measurement of the real expansion of liquid is a bit difficult because the liquid-containing vessels also expand when they come in contact with heat. So coming to talk about the apparent expansion, it is nothing but the difference between real expansion and the expansion of the vessel. When heat is applied to a container, the apparent expansivity of a liquid is the fraction of its volume by which liquid emerges to expand per kelvin rise in temperature.

The real cubical expansion is always more in liquids than the apparent cubical volume expansion

Examples

•   Expansion of the alcohol level in a thermometer because of the temperature rise.
•     On a hot summer day, gasoline drips from a newly filled tank.
•   There was an increase in mercury level in the thermometer when the thermometer came in contact with heat.

Cubical expansion coefficient

The coefficient of cubical expansion in liquids can be stated as the fractional change in its volume per kelvin or degree Celsius change in temperature.

When the water cools below 4 degrees Celsius, it begins to expand until it reaches 0 degrees Celsius. As it cools further, its volume suddenly increases as it turns into ice at 0°C. When ice is cooled below 0°C, it contracts, which means its volume decreases, just like solids. The anomalous expansion of water refers to this unusual expansion of water.

Most liquids exhibit a relatively predictable pattern of gradual volume increase in response to temperature increase and volume decrease in response to temperature decrease. The coefficient of volume expansion of a liquid is generally more significant than that of a solid, and a liquid will contract when frozen.

Gasoline exhibits an instance of liquid thermal expansion caused by temperature increase. The gasoline is relatively cool when it leaves the underground tank at the gas station but it will warm up when it sits in the tank of a previously warm car.

If the car’s tank is full and the vehicle is left in the sun, and if the vehicle is not driven once the tank is filled, the gasoline may expand in volume faster than the fuel tank, spilling onto the pavement.

Water

Water, which has a volume expansion coefficient of 2.1 in the liquid state and 0.5 in the solid state, has several interesting properties for thermal expansion. When water is cooled from its boiling point of 100°C to 4°C, it contracts steadily, just like any other substance in response to a temperature drop. However, as the substance transitions from liquid to solid, it becomes denser; this does not happen with water.

The water reaches its maximum density at 32.9°F, which means that its volume for a given unit of mass is at its smallest. Below that temperature, it should continue to decrease in volume per unit of mass, but it instead begins to expand steadily. When it reaches the freezing point, it becomes less dense, with a greater volume per unit of mass. As a result, when pipes freeze in the winter, they frequently burst, elucidating why a radiator occupied with water could be a severe problem in freezing weather. You should never use pure water in a radiator because the volume expansion coefficient of water is higher than that of a stereotypical engine coolant. This is especially dangerous in cold weather as frozen water in a radiator can expand and break the engine block.

Furthermore, this unusual thermal expansion and contraction behaviour explains why ice floats: solid water is less dense than the liquid water beneath it. As a result, frozen water remains at the lake’s surface during the winter; because ice is a poor conductor of heat, energy cannot seep from the water below it in sufficient quantities to freeze the lake water. As a result, the water beneath the ice remains liquid, preserving plant and animal life.

Conclusion

The liquid molecules have free movement. When a liquid is heated, the rate of vibration of the liquid molecules increases. The molecules push against each other and require more space to exist. This accounts for the liquid’s expansion when heated. Liquids have more significant thermal expansion than solids because of the weak forces between their molecules. As a result, liquids have a higher coefficient of volume expansion than solids.