Introduction
A thermodynamic system refers to any defined quantity of matter separated from its surroundings by physical or imaginary boundaries. Depending on these boundaries, systems can be classified as open, closed, or isolated.
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Isolated systems do not exchange matter or energy with their surroundings.
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Closed systems allow the transfer of energy but not matter.
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Open systems permit the flow of both matter and energy across their boundaries.
The study of temperature, heat, work, and their relationships with various physical properties of matter falls under thermodynamics, an essential branch of physics.
What Is Latent Heat?
Latent heat is the quantity of energy absorbed or released by a substance during a change in its physical state—such as melting, boiling, or sublimation—without causing any change in its temperature. This concept, introduced by chemist Joseph Black, is typically measured through calorimetry.
Latent heat is required to overcome the intermolecular forces binding atoms or molecules together. For example, gases have molecules that vibrate freely, while liquids and solids have stronger intermolecular attractions that require additional energy to break.
Types of Latent Heat
Latent heat is commonly classified into three categories:
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Latent heat of fusion
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Latent heat of vaporization
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Latent heat of sublimation
In the discussion below, you will also notice the incorporated keyword “types of latent heat” in context to ensure clarity and relevance.
Latent Heat of Fusion
Latent heat of fusion is the energy absorbed or released during the transition from solid to liquid. When a solid substance is heated at constant pressure, it melts into a liquid. The heat involved in this transition, without temperature change, defines the heat of fusion.
A common example is ice absorbing energy as it melts into liquid water.
Latent Heat of Vaporization
Latent heat of vaporization refers to the energy required to convert a liquid into a gas at constant temperature. When water reaches its boiling point and forms steam, it absorbs significant heat energy, demonstrating this principle.
Latent Heat of Sublimation
Latent heat of sublimation is the heat absorbed or released when a substance changes directly from solid to gas without becoming liquid.
For instance, the sublimation of ice at 0°C requires approximately 2,838 kJ/kg of energy.
Why Latent Heat Matters
Understanding phase changes is essential in meteorology, engineering, and environmental science. Interestingly, just as students benefit from learning scientific concepts with the best psle online tuition in singapore, mastering latent heat helps us understand natural and industrial processes more effectively.
Variation of Heat With Temperature
When energy is supplied to a substance, its temperature generally rises. However, during a phase change, temperature remains constant even as heat continues to flow. This plateau occurs because the supplied energy is used to break or form molecular bonds rather than increasing temperature.
Specific Latent Heat
Specific latent heat represents the energy required to change the state of one kilogram of a substance at constant temperature.
It is given by the formula:
L=QmL = \frac{Q}{m}
Where
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Q = energy absorbed or released
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m = mass of the substance
Specific Latent Heat of Water
When water is heated from room temperature, it rises to 100°C. At this point, even if heat continues to be supplied, the temperature remains steady while the water converts to steam. The relationship is expressed as:
Q=mLQ = mL
Knowing the power of the heating source allows us to calculate the specific latent heat accurately.
Latent Heat Capacity of Water
During phase transitions, the temperature of water stays constant despite continuous heating or cooling.
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When heated, water remains at 100°C until completely converted into vapor.
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When cooled, it stays at 0°C while turning into ice.
This universal property across substances reflects the energy required to change their physical state.
Summary
This article explored the nature of latent heat—energy absorbed or released during a phase change without altering temperature. It also discussed types of latent heat, specific latent heat, and the behavior of water during phase transitions.
Frequently Asked Questions
1. What is the first law of thermodynamics?
The first law states that energy cannot be created or destroyed. It relates heat, internal energy, and work as:
ΔQ=ΔU+W\Delta Q = \Delta U + W
2. What is the law of conservation of energy?
Energy cannot disappear or be created from nothing. It only transforms from one form to another.
3. Why is steam so useful in thermodynamics?
Steam has a high specific latent heat capacity, meaning it can release large amounts of energy. This makes it valuable in heating systems, power plants, and industrial processes.
4. Where is latent heat observed in daily life?
Examples include:
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Strengthening of hurricanes due to water vapor condensation
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Water freezing faster than air in refrigeration systems
5. Difference between specific heat and latent heat?
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Specific heat: Energy needed to raise the temperature of 1 kg of a substance by 1°C
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Latent heat: Energy required to change the state of 1 kg of a substance without altering temperature