Thermodynamics Chapter 12
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Questions and Answers

What is the branch of physics that deals with the concepts of heat and temperature, and the inter-conversion of heat and other forms of energy?

Thermodynamics

Thermodynamics is a microscopic science.

False

What is the unit of molar specific heat capacity of a substance?

J mol-1 K-1

What are the two modes of energy transfer to a system?

<p>Heat and work</p> Signup and view all the answers

The term "equilibrium" in thermodynamics appears in what context?

<p>State of a system where the macroscopic variables don't change in time.</p> Signup and view all the answers

What is the difference between mechanics and thermodynamics?

<p>Mechanics is concerned with the motion of the system as a whole, while thermodynamics focuses on the internal macroscopic state of the body.</p> Signup and view all the answers

The internal energy of a system depends on how that state was achieved.

<p>False</p> Signup and view all the answers

Which of the following is NOT a thermodynamic state variable?

<p>Heat</p> Signup and view all the answers

What is the first law of thermodynamics?

<p>The general law of conservation of energy applied to any system where energy transfer from or to the surroundings is taken into account.</p> Signup and view all the answers

What is the difference between specific heat capacity and molar specific heat capacity?

<p>Specific heat capacity is defined per unit mass, while molar specific heat capacity is defined per mole.</p> Signup and view all the answers

What are the two conditions under which specific heats are defined for gases?

<p>Constant volume and constant pressure.</p> Signup and view all the answers

What is the relationship between Cp and Cv for an ideal gas?

<p>Cp - Cv = R, where R is the universal gas constant.</p> Signup and view all the answers

A quasi-static process is an infinitely slow process such that the system remains in thermal and mechanical equilibrium with its surroundings.

<p>True</p> Signup and view all the answers

What is the work done by an ideal gas in an isothermal expansion from volume V₁ to V₂ at temperature T?

<p>W = μRT ln(V₂/V₁)</p> Signup and view all the answers

The internal energy of an ideal gas depends only on its temperature.

<p>True</p> Signup and view all the answers

Why are reversible processes important in thermodynamics?

<p>They achieve the highest possible efficiency for heat engines and refrigerators.</p> Signup and view all the answers

What is a Carnot cycle?

<p>A theoretical thermodynamic cycle that operates between two temperatures and achieves the maximum possible efficiency for a heat engine or refrigerator.</p> Signup and view all the answers

What is the efficiency of a Carnot engine operating between temperatures T₁ and T₂?

<p>η = 1 - T₂/T₁</p> Signup and view all the answers

The efficiency of a Carnot engine is independent of the nature of the working substance.

<p>True</p> Signup and view all the answers

What is a refrigerator?

<p>A device that extracts heat from a cold reservoir, does work on the system, and releases heat to a hot reservoir.</p> Signup and view all the answers

What is the coefficient of performance (α) of a refrigerator?

<p>α = Q₂/W, where Q₂ is the heat extracted from the cold reservoir, and W is the work done on the system.</p> Signup and view all the answers

The spontaneous processes of nature are irreversible.

<p>True</p> Signup and view all the answers

A process that is reversible is an idealised notion.

<p>True</p> Signup and view all the answers

What are the two main causes of irreversibility in thermodynamic processes?

<p>Non-equilibrium states and dissipative effects.</p> Signup and view all the answers

Study Notes

Chapter Twelve: Thermodynamics

  • Thermodynamics is the branch of physics that deals with concepts of heat and temperature, and the conversion of energy.
  • It's a macroscopic science, focusing on bulk systems rather than molecular structures.
  • Concepts like heat, temperature, work, and internal energy are more precisely defined.

12.1 Introduction

  • Thermal energy is converted to work (e.g., rubbing hands together) and vice-versa (e.g., a steam engine).
  • Historically, heat was thought of as a fluid, but now understood as a form of energy.
  • Rumford's experiment (1798) demonstrated heat as energy, not a fluid. The amount of heat produced relied on the work done, not the sharpness of the drill.

12.2 Thermal Equilibrium

  • Thermal equilibrium: a system's macroscopic variables remain constant over time.
  • This means properties like pressure, volume, temperature, mass, and composition aren't changing.

12.3 Zeroth Law of Thermodynamics

  • Two systems in thermal equilibrium with a third system are in thermal equilibrium with each other.
  • This implies a shared variable: temperature (T). If Tₐ = Tₓ and Tₓ = Tᵧ, then Tₐ = Tᵧ

12.4 Heat, Internal Energy, and Work

  • Internal energy (U) is the sum of molecular kinetic and potential energies within a system.
  • It's a state function (value depends only on the current state, not the path to get there).
  • Heat (Q) is energy transfer due to temperature difference.
  • Work (W) is energy transfer not involving a temperature difference (e.g., pushing a piston).
  • First Law of Thermodynamics: ΔQ = ΔU + ΔW (Change in heat equals change in internal energy plus change in work).

12.5 First Law of Thermodynamics

  • Internal energy can change through heat flow and work done on or by the system.
  • ΔQ = ΔU + ΔW
  • ΔQ: heat supplied to the system by the surroundings
  • ΔW: work done by the system on the surroundings
  • ΔU: change in internal energy of the system

12.6 Specific Heat Capacity

  • Specific heat (s): Amount of heat needed to raise the temperature of 1 kg of a substance by 1 K.
  • Molar specific heat (C): Amount of heat needed to raise the temperature of 1 mole of a substance by 1 K.

12.7 Thermodynamic State Variables and Equations of State

  • State variables: variables that describe a system's state (e.g., pressure, volume, temperature, mass).
  • Equations of state: relationships between state variables (e.g., the ideal gas law: PV = nRT).
  • Extensive variables: depend on the size of the system (e.g., volume, internal energy, mass).
  • Intensive variables: do not depend on the size of the system (e.g., temperature, pressure, density).

12.8 Thermodynamic Processes

  • Quasi-static process: a process that happens infinitely slowly, allowing the system to remain in equilibrium at each step.
  • Isothermal process: constant temperature.
  • Isobaric process: constant pressure.
  • Isochoric process: constant volume.
  • Adiabatic process: no heat transfer.

12.9 Heat Engines

  • Heat Engine: converts heat to work in a cyclic process.
  • A working substance undergoes a cycle of processes absorbing heat at a high temperature and rejecting heat at a low temperature, while performing work.
  • Efficiency η = (work done) / (heat input) = 1 - (heat rejected) / (heat input).

12.10 Refrigerators and Heat Pumps

  • Refrigerators are heat pumps operating in reverse.
  • They absorb heat from a cold reservoir, and reject heat to a hot reservoir, requiring work input.
  • Coefficient of Performance (COP) = (heat removed) / (work input).

12.11 Second Law of Thermodynamics

  • The Second Law of Thermodynamics limits the efficiency of a heat engine.
  • Kelvin-Planck statement: It's impossible to construct a cyclic process that absorbs heat from one reservoir and delivers an equal amount of work.

12.12 Reversible and Irreversible Processes

  • Reversible process: one in which both the system and surroundings can return to their initial states without any net change elsewhere in the universe.
  • Irreversible process: a process that cannot be exactly reversed.

12.13 Carnot Engine

  • A theoretical heat engine that operates on a cyclic process involving reversible steps.
  • It sets an upper limit on the efficiency of any heat engine between two temperatures.

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Explore the principles of thermodynamics in this quiz covering Chapter 12. Learn about thermal energy, work conversion, and the laws governing temperature and heat. Test your understanding of thermal equilibrium and historical experiments that shaped this field of physics.

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