Thermodynamics: Zeroth Law and Basic Concepts
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Questions and Answers

Which of the following is an intensive property?

  • Temperature
  • Pressure
  • Heat (correct)
  • Specific volume

    • Throttling is which type of process?

  • Adiabatic
  • Reversible
  • Irreversible (correct)
  • Isothermal

    • Why is temperature of a gas produced due to?

    kinetic energy of molecules

    What is the temperature at which a system goes under a reversible isothermal process without heat transfer?

    <p>Absolute zero temperature</p> Signup and view all the answers

    What is the work done for a constant volume process?

    <p>0</p> Signup and view all the answers

    When there is no heat exchange between two bodies at the same temperature, they are said to be in:

    <p>Thermal equilibrium</p> Signup and view all the answers

    What is another name for total heat of a substance?

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

    What is the universal gas constant in SI units equal to?

    <p>8314</p> Signup and view all the answers

    Which of the following processes is also known as an isometric process?

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

    Molar specific heat of an ideal gas depends on which two factors?

    <p>Pressure and temperature</p> Signup and view all the answers

    An adiabatic process is one in which the temperature of the gas changes.

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

    A frictionless quasi static process is called a ____________ process.

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

    Match the following with their characteristics:

    <p>Extensive Properties = Properties depending on the mass of matter present in the system Intensive Properties = Properties independent of the system's size or amount of matter</p> Signup and view all the answers

    Which law of thermodynamics forms the basis of the measurement of temperature?

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

    Which of the following is the extensive property of a thermodynamic system?

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

    Heat and work are classified as which type of properties?

    <p>Path functions</p> Signup and view all the answers

    A _________ system is exemplified by a jet engine.

    <p>constant-mass</p> Signup and view all the answers

    Internal Energy is a function of only pressure.

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

    Which of the following statements about an ideal gas is false?

    <p>Follow Charle's law</p> Signup and view all the answers

    The area under the T-S diagram curve at any thermodynamic process represents:

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

    What is enthalpy?

    <p>Internal energy + Pressure volume product</p> Signup and view all the answers

    Enthalpy is the addition of internal energy i.e. $\Delta Q = T.dS$ and product of pressure volume. $H = U + PV$. The area under the P-V diagram curve at any thermodynamic process represents ______ done.

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

    Isolated system indicates both mass and energy of substance cross the boundary.

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

    In an isothermal process, the internal energy:

    <p>Remains constant</p> Signup and view all the answers

    In a free expansion process, which of the following statements is true?

    <p>The work done is zero, but the heat transfer increases</p> Signup and view all the answers

    Which of the following are intensive properties?

    <p>Pressure, Specific Enthalpy</p> Signup and view all the answers

    Which of the following is NOT an extensive property?

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

    Of the following, which quantity is a 'path function'?

    <p>Work done</p> Signup and view all the answers

    Which of the following is the property of a system?

    <p>All of the above</p> Signup and view all the answers

    What is the latent heat of ice?

    <p>335 kJ/kg</p> Signup and view all the answers

    Specific heat is the amount of heat required to raise the temperature by what unit?

    <p>By unit degree of an unit mass</p> Signup and view all the answers

    Ice kept in a well-insulated thermoflask is an example of which system?

    <p>Isolated system</p> Signup and view all the answers

    Which of the following is an extensive property?

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

    What is the end temperature after 24 hours in a thermally insulated room undergoing a hyperbolic process with initial temperature of 50°C?

    <p>161.50°C</p> Signup and view all the answers

    In the Pressure-Volume (P-V) diagram, what does the area under the process line represent?

    <p>Heat and Work (Q and W)</p> Signup and view all the answers

    An adiabatic process is always reversible.

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

    The correct formula for converting temperature units from Celsius (C) to Fahrenheit (F) is ______.

    <p>C = (F - 32) * 5/9</p> Signup and view all the answers

    What is the gas constant (R) defined as in thermodynamics?

    <p>work per degree per mass</p> Signup and view all the answers

    Which of the following variables controls the physical properties of a perfect gas?

    <p>all of the above</p> Signup and view all the answers

    Heat transfer occurs due to temperature difference.

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

    The amount of heat required to raise the temperature of 1 kg of water by 1°C is called ________.

    <p>kilo calorie</p> Signup and view all the answers

    Which statement correctly describes the relation between specific heat at constant pressure (Cp) and specific heat at constant volume (Cv)?

    <p>Cp &lt; Cv</p> Signup and view all the answers

    What is the equivalent Fahrenheit reading for a temperature of 40°C?

    <p>1040°F</p> Signup and view all the answers

    In a steady flow process, which of the following statements is true?

    <p>Heat transfer is constant</p> Signup and view all the answers

    What is a quasi-static process?

    <p>A quasi-static process is a reversible process that proceeds very slowly, occurring when the driving force is finite but very small.</p> Signup and view all the answers

    Temperature and pressure of a perfect gas are intensive properties.

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

    The work done in the expansion of a gas from volume $V_1$ to $V_2$ under constant pressure 'P' is equal to P(V2 – V1).

    <p>P(V_2 - V_1)</p> Signup and view all the answers

    Match the expansion properties with their correct description:

    <p>n = ∞ = Constant volume process n = 1 = Isochoric process n = 1.4 = Adiabatic process n = 0 = Isobaric process</p> Signup and view all the answers

    Heat addition to a system at constant volume will increase its:

    <p>Internal energy</p> Signup and view all the answers

    What is the final temperature of a perfect gas when heated at constant pressure till its volume is doubled from 270ºC?

    <p>1086 K or 813º C</p> Signup and view all the answers

    What is the ratio of Cp to Cv of a perfect gas?

    <p>Adiabatic index</p> Signup and view all the answers

    Which gas among the following has the highest adiabatic index?

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

    What is 100ºC in Fahrenheit?

    <p>212°F</p> Signup and view all the answers

    The temperature at which the volume of a gas becomes zero is called ____________.

    <p>absolute zero temperature</p> Signup and view all the answers

    What causes the pressure exerted on the walls of a container by gas molecules?

    <p>Change their momentum due to collision with the wall</p> Signup and view all the answers

    What are the fixed points for the Celsius temperature scale?

    <p>Ice point as 0ºC and steam point as 100ºC</p> Signup and view all the answers

    What are the values of Cp and Cv for a particular ideal gas with R = 0.280 kJ/kgK and γ = 1.375?

    <p>1.0267 kJ/kg K and 0.7467 kJ/kg K</p> Signup and view all the answers

    Study Notes

    Thermodynamics

    • Zeroth law of thermodynamics forms the basis of measurement of temperature.
    • This law states that when two bodies are in thermal equilibrium with a third body, they are also in thermal equilibrium with each other.

    Basic Concepts

    • Throttling process is a constant enthalpy process or isenthalpic process.
    • Characteristics of throttling process:
      • No work transfer
      • No heat transfer
      • It is irreversible process
      • It is isenthalpic process

    Properties

    • Extensive property: Volume is an example of an extensive property.
    • Properties can be classified on the basis of size/extent of the system.

    Heat and Work

    • Heat and work are path functions.
    • They are denoted by dynamic path, so they are inexact and imperfect differential.

    Thermodynamic System

    • Thermodynamic system is a region in space upon which the study/analysis is focused.
    • Boundary is the separation between system and surrounding.

    Types of Systems

    • Open System: Mass and energy transfer take place across the boundary. (e.g. Turbine, pump, piston-cylinder arrangement with valve)
    • Closed System: No mass transfer, but energy transfer takes place. (e.g. Rigid closed container with conductive walls, piston cylinder arrangement without valve)
    • Isolated System: No mass and energy transfer takes place. (e.g. Universe, hot fluid in perfect insulated flask/container)

    Control Volume

    • Control volume in a thermodynamic system refers to a fixed region in space for thermodynamic study.
    • Examples of control volume systems include turbine impeller, pump, compressor, etc.

    Closed Thermodynamic System

    • A closed thermodynamic system is one in which there is no mass transfer, but energy transfer exists.

    Internal Energy

    • Internal energy is a function of temperature only for an ideal gas.
    • It represents the total energy associated with molecules.
    • Internal energy for an ideal gas is given by the equation U = mCvT.

    Enthalpy

    • Enthalpy is the addition of internal energy and product of pressure volume. (H = U + PV)
    • It is a compound property.
    • Enthalpy for an ideal gas is given by the equation dH = mCpdT.

    Isolated System

    • Isolated system indicates that both mass and energy of substance do not cross the boundary.
    • Examples of isolated systems include thermos flask, casserole, and universe.

    Adiabatic Process

    • A process in which no heat crosses the boundary of the system is called an adiabatic process.
    • First law of thermodynamics for closed system is given by the equation ∂Q = dU + ∂W.
    • In an adiabatic process, ∂Q = 0, so ∂W = -dU.

    Polytropic Process

    • Under certain polytropic process, value of n = 1 corresponds to isothermal process.### Thermodynamic Properties
    • Intensive properties: independent of the mass of the system, e.g. pressure, temperature, specific enthalpy, specific volume, specific energy, density, etc.
    • Extensive properties: dependent on the mass of the system, e.g. volume, energy, enthalpy, entropy, etc.
    • Note: Each specific extensive property is intensive.

    Thermodynamic Processes

    • Free expansion process: no heat is supplied or rejected, and no external work is done.
      • Q1-2 = 0, W1-2 = 0, and du = 0
      • P decreases, V increases, T remains constant (ideal gas)
    • Throttling process: an irreversible process with no change in enthalpy, and no work done.
    • Isothermal process: a process where temperature remains constant.
    • Adiabatic process: a process where no heat enters or leaves the system.
    • Isobaric process: a process where pressure remains constant.
    • Isochoric process: a process where volume remains constant.
    • Isentropic process: a process where entropy remains constant.

    Thermodynamic Systems

    • Isolated system: a system where there is no heat transfer or work done.
      • Examples: Thermos flask, Casserole, etc.
    • Open system: a system where there is heat transfer or work done.
      • Examples: Centrifugal pump, Pressure cooker, etc.

    Ideal Gas

    • Universal gas constant: 8314 J/kg-mole K or 8.314 kJ/kg-mole K.
    • Ideal gas equation: PV = nRT.
    • Charles' law: V1 / T1 = V2 / T2.

    Temperature and Heat

    • Temperature: a measure of the average kinetic energy of gas particles.
    • Heat: a form of energy transferred from one body to another due to a temperature difference.
    • Absolute zero: the lowest possible temperature, at which all particles come to rest.

    Work and Energy

    • Work done: the product of pressure and volume change.
    • Internal energy: the total energy of a system, including kinetic energy, potential energy, and potential energy.
    • Enthalpy: the total energy of a system, including internal energy and the product of pressure and volume.
    • Specific enthalpy: the enthalpy per unit mass of a system.

    Miscellaneous

    • The ratio of two specific heats of air is 1.41.
    • Density of water is maximum at 4°C.
    • The heat absorbed or rejected during a polytropic process is equal to (γ - n) / (γ - 1) × workdone.### Thermodynamics

    Adiabatic Process

    • A process in which no heat enters or leaves the gas.
    • The change in internal energy is equal to the work done.
    • Expressed by the relation, PVγ = constant, where γ is the isentropic index.
    • For monoatomic gas, γ = 1.67, for diatomic gas, γ = 1.4, and for polyatomic gas, γ = 1.33.

    Types of Processes

    • Reversible process: can be reversed bringing both the state of the system and the surroundings to the initial condition without any other inputs.
    • Irreversible process: cannot be reversed without any external inputs.
    • Isentropic process: a reversible adiabatic process.
    • Isenthalpic process: an irreversible adiabatic process.
    • Polytropic process: the most commonly used process in practice, governed by the law PVn = Const.

    Laws of Thermodynamics

    • The second law of thermodynamics: heat transfer occurs from a body at a higher temperature to a body at a lower temperature.

    Thermodynamic Properties

    • Internal energy (U): a state function, a property of the system.
    • Enthalpy (H): a state function, a property of the system.
    • Specific heat: the amount of heat required to raise the temperature of a unit mass of a substance by one degree.
    • Specific heat at constant pressure (Cp): the amount of heat required to raise the temperature of a unit mass of a substance by one degree at constant pressure.
    • Specific heat at constant volume (Cv): the amount of heat required to raise the temperature of a unit mass of a substance by one degree at constant volume.

    Heat Transfer

    • Heat transfer occurs due to temperature difference.
    • No heat transfer occurs when the temperatures of the two bodies are equal.

    P-V and T-S Diagrams

    • Area under the process line in the P-V diagram gives the work done.
    • Area under the process line in the T-S diagram gives the heat transferred.

    Thermodynamic Systems

    • Closed system: a system in which the mass of the system remains constant.
    • Open system: a system in which the mass and heat energy can be transferred to its surroundings.
    • Isolated system: a system in which no heat, work, or matter can be transferred across the boundary.

    Thermodynamic Relations

    • Cp - Cv = R/J, where R is the gas constant and J is the mechanical equivalent of heat.
    • γ = Cp / Cv, where γ is the isentropic index.

    Gas Constant

    • The gas constant (R) is the work per degree per mass.
    • The unit of gas constant (R) is N-m/kg.K or J/kg.K.
    • The value of gas constant for air is 287 J/kg.K.

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