Thermodynamics Concepts and Laws

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Questions and Answers

What does a negative ΔG indicate in a thermodynamic context?

  • The process is non-spontaneous.
  • The process is at equilibrium.
  • The process is spontaneous. (correct)
  • The process requires external work.

Which of the following statements about entropy is true?

  • Higher entropy indicates higher order.
  • Entropy measures the disorder of a system. (correct)
  • Entropy is unaffected by temperature changes.
  • Entropy measures the total energy of a system.

In thermodynamics, what does the equation ΔU = Q - W represent?

  • The change in Gibbs free energy of a system.
  • The relationship between entropy and heat transfer.
  • The change in internal energy of a system. (correct)
  • The work done by a system on its surroundings.

How do refrigeration systems utilize thermodynamic principles?

<p>They absorb heat from a cold reservoir and release it to a hot reservoir. (C)</p> Signup and view all the answers

What principle does thermodynamics provide in relation to chemical reactions?

<p>They govern the feasibility and spontaneity of reactions. (C)</p> Signup and view all the answers

Which of the following statements accurately describes an isolated system?

<p>It cannot exchange energy or matter with its surroundings. (D)</p> Signup and view all the answers

What does the First Law of Thermodynamics state regarding energy?

<p>Energy cannot be created or destroyed, only transformed. (A)</p> Signup and view all the answers

Which of the following processes occurs at a constant temperature?

<p>Isothermal process (D)</p> Signup and view all the answers

Which statement correctly reflects the relationship between heat and work in thermodynamics?

<p>Heat is energy transfer due to temperature differences, while work is due to force acting through a displacement. (C)</p> Signup and view all the answers

According to the Second Law of Thermodynamics, what happens to the total entropy of an isolated system?

<p>It increases or remains constant in all cases. (B)</p> Signup and view all the answers

Which of the following best defines a closed system?

<p>It exchanges energy but not matter with its surroundings. (C)</p> Signup and view all the answers

What is a characteristic feature of the Third Law of Thermodynamics?

<p>Entropy approaches zero as the temperature approaches absolute zero. (D)</p> Signup and view all the answers

Which of these options represents a path function in thermodynamics?

<p>Work (C)</p> Signup and view all the answers

Flashcards

Internal Energy (U)

The total energy stored within a system, including the kinetic energy of its molecules and their potential energy due to their interactions.

Entropy (S)

A measure of the disorder or randomness of a system. Higher entropy means greater disorder.

Gibbs Free Energy (G)

A thermodynamic potential that measures the maximum reversible work that may be performed by a thermodynamic system at constant temperature and pressure. A negative ΔG indicates a spontaneous process.

Power Plants

Power plants convert heat energy into mechanical energy. Thermodynamics helps us design and understand these systems.

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Engines

Thermodynamics explains how heat engines operate, converting heat into work. They use this conversion to do useful things like power vehicles.

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Thermodynamics

The study of energy and its transformations, focusing on macroscopic properties (like temperature and pressure) rather than microscopic details.

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Thermodynamic System

A collection of matter and energy that is being observed, separated from its surroundings.

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Isolated System

A system that exchanges neither energy nor matter with its surroundings. It's completely isolated.

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Closed System

A system that exchanges energy but not matter with its surroundings. Think of a closed container like a pressure cooker.

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Open System

A system that exchanges both energy and matter with its surroundings. An open cup of coffee is an example.

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Thermodynamic Process

A change in the state of a system. It can be a change in temperature, pressure, volume, etc.

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Isothermal Process

A process that occurs at a constant temperature. It is a common type of thermodynamic process. Think of a pot of water simmering on a stove.

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Study Notes

Basic Concepts

  • Thermodynamics is the study of energy and its transformations. It focuses on macroscopic system properties, not microscopic details.
  • Systems are collections of matter and energy under observation. The surroundings encompass everything outside the system.
  • Isolated systems exchange neither energy nor matter with their surroundings.
  • Closed systems exchange only energy with their surroundings, not matter.
  • Open systems exchange both energy and matter with their surroundings.
  • A thermodynamic process is a change in a system's state.

Laws of Thermodynamics

  • Zeroth Law: Two systems in thermal equilibrium with a third are in equilibrium with each other. This defines temperature.
  • First Law: Energy cannot be created or destroyed, only transferred. The change in a system's internal energy equals heat added minus work done by the system (ΔU = Q - W).
  • Second Law: The total entropy of an isolated system increases over time (or remains constant for reversible processes). Systems naturally move toward disorder. Spontaneous processes increase the universe's entropy.
  • Third Law: The entropy of a perfect crystalline substance approaches zero as the temperature approaches absolute zero.

Thermodynamic Systems and Processes

  • State functions: Properties depending only on the system's current state, not the path. Examples: internal energy (U), enthalpy (H), entropy (S), Gibbs free energy (G).
  • Path functions: Properties depending on the path taken, not just the initial and final states. Examples: heat (Q) and work (W).
  • Isothermal process: A constant-temperature process.
  • Adiabatic process: A process with no heat exchange with the surroundings.
  • Isobaric process: A constant-pressure process.
  • Isochoric process: A constant-volume process.

Concepts of Heat and Work

  • Heat (Q): Energy transfer due to a temperature difference. Heat flows from warmer to cooler objects.
  • Work (W): Energy transfer associated with a force acting over a distance. Work done on a system is positive; work done by a system is negative.
  • Internal Energy (U): The total energy stored within a system, including molecular kinetic and potential energies.

Entropy and Free Energy

  • Entropy (S): A measure of system disorder or randomness. Higher entropy means greater disorder.
  • Gibbs Free Energy (G): A thermodynamic potential, measuring the maximum reversible work at constant temperature and pressure. A negative ΔG indicates a spontaneous process.

Applications of Thermodynamics

  • Power plants: Thermodynamics is key in designing and analyzing power plants. Heat energy becomes mechanical energy.
  • Refrigeration: Refrigeration systems transfer heat from cold to hot reservoirs.
  • Chemical reactions: Thermodynamics predicts the feasibility and spontaneity of chemical reactions.
  • Engines: Thermodynamics explains heat engine operation, converting heat into work efficiently.
  • Phase transitions: Principles of thermodynamics explain phase changes (melting, boiling, etc.).

Key Equations

  • ΔU = Q - W
  • ΔG = ΔH - TΔS

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