Energy Flow and Thermodynamics

Energy Flow

Introduction

• Energy is the capacity to do work and is essential in various situations.
• The law of conservation of energy states that energy cannot be created or destroyed, only converted from one form to another.
• Efforts are made to convert energy from less useful forms to more useful forms.

Examples of Energy Conversion

1. Electrical to Heat Energy:

   • An electrical room heater converts electrical energy into heat energy.
   • A thermocouple converts heat energy into electrical energy.

2. Chemical to Electrical Energy:

   • Chemical reactions in a cell produce electrical energy.
   • Electrolysis uses electrical energy to cause chemical changes/reactions.

3. Mechanical to Electrical Energy:

   • A generator converts mechanical energy into electrical energy.
   • An electric motor converts electrical energy into mechanical energy (rotation of blades).

4. Potential to Kinetic Energy:

   • Potential energy stored in a pulled bowstring converts into kinetic energy of the arrow upon release.

5. Sound to Electrical Energy

   • A microphone converts sound energy into electrical energy.
   • A loudspeaker converts electrical energy into sound energy.

Linear Flow of Energy

• Energy conversion is often a linear flow, not always reversible.

• Example: Potential energy of water in a dam converts to electrical energy, then to heat and light, and finally to chemical energy.

  Mechanical\ Energy \rightarrow Electrical \ Energy \rightarrow Heat \ and \ Light \ Energy \rightarrow Chemical \ Energy

Forms of Energy

• Various forms of energy include: mechanical (kinetic and potential), heat, chemical, electrical, sound, light, nuclear, and solar energy.
• Interconversion between these forms is constantly occurring.

Examples of Energy Conversion in Nature and Technology

• Nuclear energy converts into heat and light in the sun.
• An electric bulb transforms electrical energy into light and heat.
• A steam engine transforms heat energy into mechanical energy.
• An electric cell transforms chemical energy into electrical energy.
• A microphone transforms sound energy into electrical energy.
• Nuclear reactors use nuclear energy to produce electricity.
• An electric fan or motor transforms electrical energy into mechanical energy.

Principle of Conservation of Energy

• Energy conversion raises the question of whether it's a complete or partial conversion.
• Scientists initially explored the possibility of continuously creating energy for perpetual motion machines.
• It was realized that energy cannot be created or destroyed, only converted.
• The 'final total energy' always equals the 'initial total energy'.
• This principle is known as the law of conservation of energy.

Statements of the Law of Conservation of Energy:

1. 'The total energy content of the universe remains constant or conserved.'
2. 'Total energy of an isolated system remains constant.'
3. 'Energy can neither be created nor destroyed.'
4. 'Whenever any conversion of energy from one form to one or more forms takes place, the final total energy is always equal to the initial total energy.'

• The law is a fundamental law of nature and a strong pillar of science and physics.

Efficiency of Energy Transfer

• Energy conversion is almost never complete.

• Input energy invariably converts into some 'undesired energy'.

• Total energy output equals total input energy, according to the law of conservation of energy.

• Efficiency of energy transfer is not unity or 100%.

  Efficiency = \frac{Output \ energy \ obtained}{Input \ energy}

• Multiply the fraction by 100 to get the percentage of efficiency.

Energy Transfer and Thermodynamics

• Thermodynamics is the branch of science concerned with the conversion of heat energy into other forms of energy and vice versa.
• The first law of thermodynamics states that energy is conserved and can only be transferred from one form to another.
• The second law of thermodynamics states that a heat engine can never be 100% efficient.
• Heat energy supplied to a heat engine can never be completely converted into mechanical work.

Second Law of Thermodynamics and Heat Flow:

• Heat flows from a body at higher temperature to one at a lower temperature, irrespective of total heat energy content.
• For example, heat energy flows from a hot cup of tea to the surrounding atmosphere.
• Temperature, not total heat energy content, determines the direction of heat flow.

Food Chain as a Flow of Energy

• Plants produce their own food; other life forms consume plants or other life forms for energy.

• This creates a food chain involving a linear flow of energy.

• The primary source of energy is the sun.

• Plants absorb solar energy and use a small part (~0.02%) in photosynthesis to produce food.

  • Plants are referred to as producers.
  • Total energy stored in plants is gross primary production.
  • The energy left over after respiration, is known as net primary production.

• Plants are consumed by herbivores (primary consumers).

  • Primary consumers intake energy nearly equal to net primary production.
  • They store some energy as food and use the rest for metabolic processes (respiration).

• Primary consumers are consumed by secondary consumers (carnivores).

  • Their intake is less than or equal to the energy stored in primary consumers.
  • Secondary consumers use part of the energy for metabolic process.

• Tertiary consumers consume secondary consumers.

  • Energy left for storage in tertiary consumers becomes very low, limiting further chain continuation.
  • Humans may consume tertiary consumers.

• Energy flow is linear, with progressively reducing amounts from producers to tertiary consumers.

• The food chain stops at tertiary consumers due to lack of energy.

• The process is not cyclic because there is no flow back of energy to the producers.

  Sun \rightarrow Producers \rightarrow Primary\ Consumers \rightarrow Secondary\ Consumers \rightarrow Tertiary\ Consumers

• (E₁ - E), (E₂ - E), (E₃ - E) represent the energy used in respiration and metabolic processes.

• The law of conservation of energy is valid in all energy transfers.

• The non-cyclic nature aligns with the second law of thermodynamics, which rules out energy flow in certain directions.

Cycles in Nature

• Interactions between biotic and abiotic components make the biosphere a stable but dynamic system.
• These dynamic interactions are viewed through cycles in nature.

Well-known cycles:

1. Water Cycle
2. Nitrogen Cycle
3. Carbon Cycle
4. Oxygen Cycle

• Matter and energy are transferred between constituents.
• Water, nitrogen, carbon, and oxygen are repeatedly cycled, maintaining the biosphere as a stable system.
• Linear flow: motion of a particle along a straight path.
• Cycle: motion of a particle in a circle.
• Contrast: Cycles vs linear flow of energy.