Grade 9
  1. Mechanics  1.1. Motion  1.1.1. Types of motion  1.1.2. Distance and displacement  1.1.3. Speed and Velocity  1.1.4. Acceleration  1.1.5. Graphical representation of motion  1.1.6. Equations of motion  1.1.7. Uniform and non-uniform motion  1.1.8. Free fall and acceleration due to gravity  1.1.9. Relative speed  1.1.10. Circular motion  1.2. Laws of force and motion  1.2.1. The concept of force  1.2.2. newton's first law of motion  1.2.3. Newton's second law of motion  1.2.4. Newton's third law of motion  1.2.5. Inertia and types of inertia  1.2.6. Motion  1.2.7. Conservation of momentum  1.2.8. Application of Newton's laws in daily life  1.2.9. Types of Forces (Contact and Non-Contact)  1.2.10. Friction and its effects  1.3. Gravitational force  1.3.1. Newton's law of universal gravitation  1.3.2. Importance of Gravitational Force  1.3.3. Acceleration due to gravity  1.3.4. Free fall and weightlessness  1.3.5. Mass and weight  1.3.6. Variation of g with height and depth  1.3.7. Kepler's laws of planetary motion  1.3.8. Satellites and their orbits  1.4. Work, Energy and Power  1.4.1. Concept of work  1.4.2. Positive and negative actions  1.4.3. Work done by constant and variable force  1.4.4. Energy and its forms  1.4.5. Kinetic energy and potential energy  1.4.6. Law of conservation of energy  1.4.8. Commercial unit of energy  1.4.9. Work–energy theorem  1.5. Simple machines  1.5.1. Types of simple machines  1.5.2. Mechanical advantage  1.5.3. Machine efficiency  1.5.4. Levers and their types  1.5.5. Pulleys and Inclined Planes  1.5.6. Gears and their uses
  2. Properties of matter  2.1. States of matter  2.1.1. Solids, liquids and gases  2.1.2. Properties of different states of matter  2.1.3. Change in state of matter  2.1.4. Plasma and Bose–Einstein condensate  2.2. Density and pressure  2.2.1. Concept of density and relative density  2.2.2. Pressure in solids, liquids and gases  2.2.3. Pascal's law and its applications  2.2.4. Atmospheric pressure and its variations  2.2.5. Surface tension and capillarity  2.3. Buoyancy and Archimedes' principle  2.3.1. Buoyant force  2.3.2. Archimedes principle  2.3.3. Applications of Archimedes' Principle  2.3.4. floating and sinking objects  2.3.5. Theory of Flotation and Archimedes' Principle
  3. Heat and Thermodynamics  3.1. Temperature and heat  3.1.1. Concept of heat and temperature  3.1.2. Temperature measurement  3.1.3. Temperature scales  3.2. Heat transfer  3.2.1. Conduction of heat  3.2.2. Convection of heat  3.2.3. heat radiation  3.2.4. Applications of heat transfer  3.2.5. Thermal conductivity  3.3. Thermal expansion  3.3.1. Expansion of solids, liquids and gases  3.3.2. Abnormal expansion of water  3.3.3. Applications of Thermal Expansion  3.4. Specific heat capacity and latent heat  3.4.1. Concept of specific heat capacity  3.4.2. Measurement and applications of specific heat  3.4.3. Latent heat of fusion and vaporization  3.4.4. Heat Engines and Efficiency
  4. Waves and sound  4.1. Waves and their types  4.1.1. Mechanical and electromagnetic waves  4.1.2. Longitudinal and Transverse Waves  4.1.3. Properties of Waves  4.1.4. Wavelength, frequency and speed of the wave  4.1.5. Superimposition of waves  4.2. Sound waves  4.2.1. Nature and transmission of sound  4.2.2. Speed of sound in different mediums  4.2.3. Reflection of sound and echo  4.2.4. Sonar and ultrasound  4.2.5. Resonance and pulsation  4.3. Sound characteristics  4.3.1. Intensity, loudness and quality of sound  4.3.2. Doppler effect in sound
  5. Lighting and Optics  5.1. Reflection of light  5.1.1. Laws of reflection  5.1.2. Reflection from a plane mirror  5.1.3. Reflection from a spherical mirror  5.1.4. Image formation by concave and convex mirrors  5.1.5. Applications of Reflection  5.2. Refraction of light  5.2.1. Laws of refraction  5.2.2. Refractive index  5.2.3. Refraction through a glass slab  5.2.4. Refraction in water and air  5.2.5. Lenses and their types  5.2.6. Image formation by convex and concave lenses  5.2.7. Total internal reflection and its applications  5.3. Dispersion and scattering of light  5.3.1. Spectrum of white light  5.3.2. Prisms and Dispersion  5.3.3. Tyndall effect and blue sky
  6. Electricity and Magnetism  6.1. Electric charge and static electricity  6.1.1. The concept of electric charge  6.1.2. Charging by friction, contact and induction  6.1.3. Electroscope and its working  6.2. Current Electricity  6.2.1. The concept of electric current  6.2.2. Ohm's Law and Resistance  6.2.3. Factors affecting resistance  6.2.4. Series and Parallel Circuits  6.2.5. Heating effect of electric current  6.2.6. Electric power and energy  6.3. Magnetism  6.3.1. Natural and artificial magnets  6.3.2. Properties of magnets  6.3.3. Earth's magnetism  6.3.4. Magnetic field and field lines  6.3.5. Electromagnets and their applications
  7. Modern Physics  7.1. structure of the atom  7.1.1. Atomic Structure and Subatomic Particles  7.1.2. Electrons, Protons, and Neutrons  7.1.3. Rutherford and Bohr model  7.2. Radioactivity  7.2.1. Types of radioactive emissions  7.2.2. Half-life and radioactive decay  7.2.3. Uses and Hazards of Radioactivity
  8. Space science and astronomy  8.1. The universe and its components  8.1.1. Stars and galaxies  8.1.2. Planets and Solar System  8.2. Satellites  8.2.1. Natural and artificial satellites  8.2.2. Use of satellites

Grade 9 → Heat and Thermodynamics → Specific heat capacity and latent heat ↓


Latent heat of fusion and vaporization


In the study of heat and thermodynamics, it is essential to understand how energy affects matter during phase transitions. The most basic concepts associated with these transitions include latent heat of fusion and latent heat of vaporization . These concepts describe the energy required for substances to change phase without a change in temperature.

Overview of heat, temperature, and phase changes

Before we dive into latent heat, let's take a brief overview of some basic principles:

1. Heat and temperature

- Heat is energy in transit due to a temperature difference. When we talk about adding heat or removing heat, we are talking about the transfer of energy from one form of matter to another.

- Temperature is a measure of the average kinetic energy of the particles in a substance. Higher temperature means higher average kinetic energy.

2. Specific heat capacity

Specific heat capacity is the amount of heat needed to raise the temperature of one kilogram of a substance by one degree Celsius. It is a measure of how much energy a substance can store. The formula for calculating the energy needed to change the temperature of a substance is:

Q = mcΔT

Where:

  • Q is the heat absorbed or released,
  • m is the mass of the substance,
  • c is the specific heat capacity,
  • ΔT is the change in temperature.

Remember that this formula only applies to temperature changes, not phase changes. This is where latent heat comes into play.

3. Phase change

Matter changes phase or state when it transitions between solid, liquid, and gas. Common phase transitions include:

  • Fusion (melting): transition from solid to liquid.
  • Freezing: Change from a liquid to a solid.
  • Vaporization (boiling): The transition from liquid to gas.
  • Condensation: The transition from a gas to a liquid.
  • Sublimation: Transition from solid to gas.
  • Deposition: Change from a gas to a solid.

Understanding latent heat

Latent heat refers to the amount of heat absorbed or released by a substance during a phase change without a change in temperature. The word "latent" comes from the Latin word "latere", meaning hidden, because the energy involved does not appear as a temperature change but as a change in state. Latent heat can be of two types depending on the phase change:

1. Latent heat of fusion

Latent heat of fusion is the heat energy required to convert a unit mass of a solid into a liquid at its melting point without any change in temperature. This energy breaks the intermolecular forces holding the solid together.

Q_f = mL_f

Where:

  • Q_f is the heat absorbed or released during fusion,
  • m is the mass of the substance,
  • L_f is the latent heat of fusion.

For example, when ice melts into water, it requires a certain amount of heat for each kilogram of ice, without raising the temperature above 0° C. The latent heat of fusion for ice is about 334,000 J/kg.

solid to liquid: melting

2. Latent heat of vaporization

Latent heat of vaporization is the heat energy required to convert a unit mass of a liquid at its boiling point into a gas without any change in temperature. This energy overcomes the intermolecular forces between the liquid particles to form a gaseous state.

Q_v = mL_v

Where:

  • Q_v is the heat absorbed or released during vaporization,
  • m is the mass of the substance,
  • L_v is the latent heat of vaporization.

For example, converting water into steam requires a considerable amount of energy, since the latent heat of vaporization of water is about 2,260,000 J/kg.

Liquid to Gas: Boiling

Visualization of phase transitions and heat

To better understand how heat affects a substance during a phase change, let's consider the temperature curve of water. This curve shows the changes in temperature over time as heat is continuously added:

Temperature ^ |  (Vaporization)
(Boiling)--------------------
                  |     |     |     |     |
                  |     |
                  (Melting)-----
                                    (Heating of | the liquid)
                  |
 (Heating of | the solid)
 --------------------------> Time

Observe the following steps in the heating curve:

  • Heating a solid (ice): As heat is absorbed the temperature increases until it reaches the melting point.
  • Melting: The temperature remains constant as the ice melts. The heat input is used as latent heat of fusion.
  • Heating a liquid (water): As heat is absorbed the temperature increases until it reaches the boiling point.
  • Boiling: The temperature remains constant as water turns into steam. The heat input is used as latent heat of vaporization.

Practical example

1. Ice melting into water

Consider a 0.5 kg piece of ice at 0°C. To calculate the amount of energy needed to convert this ice into water at 0°C, we will use the latent heat of fusion.

Q_f = mL_f
Q_f = 0.5 kg × 334,000 J/kg = 167,000 J

Thus, 167,000 joules of energy are required to convert ice into water without raising the temperature.

2. Boiling of water into steam

If you have 1 kg of water at 100°C and you want to convert it into steam at 100°C, we use the latent heat of vaporization.

Q_v = mL_v
Q_v = 1 kg × 2,260,000 J/kg = 2,260,000 J

This transformation requires 2,260,000 joules of energy.

Applications of latent heat

Understanding latent heat is important in a variety of fields, including:

  • Climate science: Latent heat of fusion from melting glaciers and sea ice is affecting climate models.
  • Engineering: Design and optimization of heat exchangers that utilize latent heat for effective thermal regulation.
  • Food industry: Freeze drying and preservation techniques involve controlling latent heat exchange.
  • Meteorology: Energy from latent heat affects storms and weather patterns through the phase changes of water.

Conclusion

Latent heat plays an important role in the phase transitions of substances without a change in temperature. Latent heat of fusion and latent heat of vaporization describe the energy required to change phases between solid/liquid and liquid/gas, respectively. This concept is central to understanding many natural phenomena and technological applications in the world around us.


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Latent heat of fusion and vaporization

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