BE2103 Thermodynamics in Biosystem Module 3 Segment 4

Summary

This lecture explores the First Law of Thermodynamics within biosystems, emphasizing the principle of energy conservation. It explains how energy can neither be created nor destroyed, only transformed among forms such as heat, work, kinetic, potential, and internal energy. Using examples like falling rocks and adiabatic processes, the lecture illustrates energy transfer mechanisms and introduces the concept of total energy. It also covers energy balance equations for closed and flowing systems, highlighting stationary systems where kinetic and potential energy changes are negligible. The session lays a foundational understanding for analyzing energy interactions and sets the stage for future discussions on energy conversion and efficiency.

Takeaways

• 😀 The first law of thermodynamics, also known as the conservation of energy principle, states that energy cannot be created or destroyed, only transformed from one form to another.
• 😀 Energy in a system can exist in multiple forms, including internal, kinetic, potential, electric, and magnetic energy.
• 😀 Total energy change in a system during a process depends only on the initial and final states, not on the path taken.
• 😀 For stationary systems, changes in kinetic and potential energies are negligible, so total energy change equals the change in internal energy.
• 😀 Energy can be transferred to or from a system via heat, work, or mass flow.
• 😀 Heat transfer to a system increases its internal energy, while heat transfer from a system decreases it.
• 😀 Work done on a system increases its energy, while work done by the system decreases it.
• 😀 Mass entering a system carries energy into the system, while mass leaving a system removes energy.
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• 😀 The energy balance equation expresses the net change in a system’s energy as the difference between energy entering and leaving via heat, work, and mass flow.
• 😀 For adiabatic systems, heat transfer is zero, and for systems with no work interaction, work transfer is zero.
• 😀 The first law of thermodynamics provides a foundation for analyzing energy conversions, system efficiencies, and understanding energy interactions in biosystems.
• 😀 Arbitrary reference values can be assigned to total energy at a specified state, as only changes in energy are physically meaningful.

Q & A

What is the First Law of Thermodynamics?

The First Law of Thermodynamics, also known as the conservation of energy principle, states that energy cannot be created or destroyed, only transformed from one form to another. It emphasizes that every bit of energy must be accounted for during a process.

How does the example of a falling rock illustrate the First Law?

The falling rock demonstrates energy transformation: its potential energy decreases as it falls, while its kinetic energy increases by the same amount, assuming negligible air resistance. This illustrates that energy is conserved, merely changing form.

What is the significance of adiabatic processes in the First Law?

In adiabatic processes, no heat transfer occurs. Experiments show that the work done between two specified states is independent of the process details. This observation supports the definition of total energy as a state property in thermodynamics.

What does 'total energy' of a system consist of?

Total energy includes the sum of internal energy, kinetic energy, potential energy, and, if relevant, electric and magnetic energies. It represents the complete energy content of the system at a given state.

Why does the First Law focus on changes in energy rather than absolute values?

The First Law emphasizes changes because the total energy of a system can be arbitrarily assigned at a reference state. What matters for energy analysis is how energy changes during a process, not the absolute value at a particular state.

How is energy transferred to or from a system?

Energy is transferred through heat (Q), work (W), and mass flow. Heat transfer changes the internal energy, work changes the total energy by energy interaction at the boundary, and mass flow adds or removes energy depending on the energy carried by the entering or exiting mass.

What simplifications occur for stationary systems in energy calculations?

For stationary systems, changes in kinetic and potential energies are negligible. Thus, the total energy change reduces to the change in internal energy alone, simplifying the energy balance to ΔE = ΔU.

How is the energy balance expressed mathematically for any system?

The energy balance can be expressed as ΔE_system = E_in - E_out, where E_in and E_out account for energy entering and leaving via heat, work, and mass. This can be applied in various forms: per unit mass, per unit time, differential form, or for cyclic processes.

What is the energy balance for a closed system undergoing a cycle?

For a closed system with a cyclic process, the net work output during the cycle is equal to the net heat input. Mathematically, W_net = Q_net, illustrating energy conservation over the cycle.

What are the special cases for energy transfer terms in the energy balance?

Special cases include adiabatic systems (Q = 0), systems with no work interactions (W = 0), and systems with no mass flow across boundaries (E_mass = 0). These conditions simplify the general energy balance equation.

Why is the First Law considered a fundamental principle based on experiments?

The First Law is based on experimental observations, such as Joule's experiments on adiabatic processes, which showed consistent work outcomes regardless of process details. It cannot be derived from other physical principles, making it fundamental.

How does mass flow contribute to the energy of a system?

Mass entering a system carries energy with it, increasing the system's total energy. Conversely, mass leaving the system removes energy. This mechanism complements heat and work as a form of energy transfer.