Thermodynamic Processes 50 mcq’s
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Polytropic processes are significant in:
Explanation: Gas compressors often follow polytropic processes due to combined heat and work effects. Calorimeters, condensers, and evaporators involve other processes
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In a polytropic expansion, temperature:
Explanation: Temperature change varies with n (e.g., decreases for n > 1, constant for n = 1). It’s not universally increasing or decreasing.
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The polytropic index n for an adiabatic process equals:
Explanation: Adiabatic processes follow PV^γ = constant, where γ is the specific heat ratio. Other n values represent different processes.
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When n = 0, a polytropic process becomes:
Explanation: For n = 0, PV^0 = constant, implying constant pressure, an isobaric process. Other processes correspond to different n values.
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Polytropic processes are commonly analyzed in:
Explanation: Piston-cylinders allow volume and pressure changes, ideal for polytropic processes. Rigid containers, pipes, or heat exchangers involve other conditions.
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For an ideal gas in a polytropic process, heat transfer:
Explanation: Heat transfer varies with n, as Q = ΔU + W, and n affects both terms. It’s not inherently zero, equal to work, or negative
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A polytropic process with n = ∞ represents:
Explanation: When n = ∞, volume is constant (PV^∞ = constant), indicating an isochoric process. Other processes have finite n values.
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In a polytropic process, work done depends on:
Explanation: Work is calculated as W = PΔV/(1-n), driven by volume change. Temperature, enthalpy, or entropy are secondary in work calculations.
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The polytropic index n equals 1 for
Explanation: For ideal gases, n = 1 gives PV = constant, characteristic of isothermal processes. Adiabatic, isobaric, and isochoric have different n values.
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A polytropic process follows the relation:
Explanation: Polytropic processes obey PV^n = constant, where n is the polytropic index. Other relations apply to isothermal, isochoric, or isobaric processes
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In an isobaric expansion of an ideal gas:
Explanation: Expansion requires heat absorption to maintain pressure and increase enthalpy. Work is done by the system; temperature typically rises.
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Isobaric processes are significant in:
Explanation: Boilers operate at constant pressure, heating fluids in isobaric conditions. Calorimeters are isochoric; nozzles and turbines often involve adiabatic processes.
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In an isobaric process, internal energy change is:
Explanation: Internal energy change (ΔU = m·cv·ΔT) depends on temperature via cv. It’s not zero, work, or inherently negative in isobaric processes.
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For an ideal gas in an isobaric process, V/T is:
Explanation: From the ideal gas law (PV = nRT) at constant pressure, V/T = nR/P = constant. Other behaviors apply to different processes.
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An isobaric process is typically modeled in:
Explanation: Piston-cylinders allow volume changes at constant pressure, ideal for isobaric processes. Rigid containers fix volume; insulated systems may be adiabatic.
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In an isobaric process for an ideal gas:
Explanation: Heat addition changes temperature and volume at constant pressure (PV = nRT). Volume isn’t fixed, pressure is constant, and internal energy varies.
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Specific heat at constant pressure (cp) is used in:
Explanation: cp governs heat addition in constant-pressure processes (Q = m·cp·ΔT). cv is for isochoric; other processes have different heat relations.
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For an ideal gas in an isobaric process, heat added equals:
Explanation: Heat at constant pressure increases enthalpy (Q = ΔH = m·cp·ΔT). Internal energy and work are partial components of this heat.
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In an isobaric process, work done is given by:
Explanation: Work in isobaric processes is W = PΔV due to volume change at constant pressure. Zero work applies to isochoric; other terms relate to energy changes.
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An isobaric process occurs at:
Explanation: Isobaric processes maintain constant pressure, with heat and work affecting volume and temperature. Volume, temperature, or entropy may change, unlike isochoric or isothermal processes.
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In an isochoric process with heat addition:
Explanation: Heat addition increases internal energy (ΔU = Q) as no work is done. Temperature rises, but volume remains constant.
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Isochoric processes are significant in:
Explanation: Bomb calorimeters use constant-volume conditions to measure heat of reactions. Turbines, nozzles, and heat exchangers involve flow or other processes.
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In an isochoric process, enthalpy change is:
Explanation: Enthalpy change (ΔH = m·cp·ΔT) depends on temperature change and cp. It’s not zero, work-related, or inherently negative.
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For an ideal gas in an isochoric process, pressure and temperature are related by:
Explanation: From the ideal gas law (PV = nRT) at constant volume, P/T = nR/V = constant. Other relations apply to isothermal or adiabatic processes.
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An isochoric process is typically modeled in:
Explanation: Rigid containers maintain constant volume, ideal for isochoric processes. Piston-cylinders allow volume changes; pipes and turbines involve flow.
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In an isochoric process for an ideal gas:
Explanation: Internal energy of ideal gases depends on temperature, which changes with heat addition. Volume is fixed, and pressure or temperature may vary.
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Specific heat at constant volume (cv) is used in:
Explanation: cv governs heat addition in constant-volume processes (Q = m·cv·ΔT). cp is used for isobaric; other processes have different heat relations.
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For an ideal gas in an isochoric process, heat added equals:
Explanation: With W = 0, the First Law (ΔU = Q – W) gives Q = ΔU. All heat increases internal energy, not work or enthalpy.
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In an isochoric process, work done is:
Explanation: No volume change (ΔV = 0) means no PV work (W = PΔV = 0). Heat transfer drives internal energy changes instead.
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An isochoric process occurs at:
Explanation: Isochoric processes maintain constant volume, with heat affecting internal energy. Pressure, temperature, or enthalpy may change, unlike isobaric or isothermal processes.
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An example of a real-world adiabatic process is:
Explanation: Rapid compression in a tire pump is nearly adiabatic due to minimal heat transfer. Boiling, heating, and cooling involve significant heat exchange.
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For an ideal gas in an adiabatic process, enthalpy:
Explanation: Enthalpy (h = u + Pv) changes with temperature and pressure variations in adiabatic processes. It’s not inherently constant, unlike isothermal ideal gas enthalpy.
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The slope of an adiabatic curve on a PV diagram is:
Explanation: Adiabatic curves (PV^γ = constant) are steeper due to γ > 1, compared to isothermal (PV = constant). They aren’t linear or flatter.
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Adiabatic processes are significant in:
Explanation: Turbines often assume adiabatic conditions for rapid expansion/compression. Boilers, condensers, and evaporators involve heat transfer, not adiabatic processes.
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In an adiabatic compression of an ideal gas:
Explanation: Work done on the gas increases internal energy, raising temperature. Work is done on the system; pressure rises, and internal energy increases.
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The relation PV^γ = constant applies to:
Explanation: For ideal gases, PV^γ = constant (γ = cp/cv) governs adiabatic processes. Isothermal uses PV = constant; isobaric and isochoric have different relations.
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Adiabatic processes are typically modeled in:
Explanation: Piston-cylinders allow volume changes and work in adiabatic processes, often insulated. Heat exchangers involve heat; rigid containers limit work.
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In an adiabatic expansion of an ideal gas:
Explanation: Expansion work reduces internal energy, lowering temperature in adiabatic processes. Constant temperature is isothermal; compression increases temperature.
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For an ideal gas in an adiabatic process, the First Law implies:
Explanation: With Q = 0, the First Law (ΔU = Q – W) becomes ΔU = -W, so internal energy changes due to work. Heat or combined terms don’t apply.
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An adiabatic process is characterized by:
Explanation: Adiabatic processes have no heat exchange (Q = 0), often due to insulation or rapid changes. Temperature, pressure, or work may vary, unlike isothermal or isobaric processes.
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For an ideal gas in an isothermal process, enthalpy:
Explanation: Enthalpy (h = u + Pv) depends on temperature for ideal gases, so it’s constant in isothermal processes. Internal energy and PV terms balance out.
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Isothermal processes are significant in:
Explanation: Isothermal processes are key in idealized heat engine cycles like the Carnot cycle. Turbines, nozzles, and rigid tanks involve other processes like adiabatic.
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In an isothermal compression of an ideal gas:
Explanation: Compression requires work input, and to maintain constant temperature, heat is rejected (Q = W). This balances the First Law with ΔU = 0.
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An isothermal process is best represented by:
Explanation: On a PV diagram, isothermal processes follow PV = constant (hyperbola) for ideal gases. Adiabatic curves are steeper; linear/parabolic don’t apply.
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The work done in an isothermal process depends on:
Explanation: Work in isothermal processes (W = nRT ln(V₂/V₁)) is driven by volume change. Constant temperature and zero ΔU shift focus to volume ratios.
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For an ideal gas undergoing isothermal expansion:
Explanation: In isothermal expansion, volume increases, and by the ideal gas law (PV = nRT), pressure decreases at constant temperature. Temperature remains unchanged.
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Isothermal processes are typically analyzed in:
Explanation: Piston-cylinders allow volume changes, enabling work and heat transfer in isothermal processes. Rigid containers or insulated systems limit such interactions.
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In an isothermal process, heat added is equal to:
Explanation: For ideal gases, ΔU = 0, so by the First Law (ΔU = Q – W), Q = W. Heat input fully converts to work output in isothermal processes.
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For an ideal gas in an isothermal process, internal energy:
Explanation: Internal energy of an ideal gas depends only on temperature, so ΔU = 0 in isothermal processes. Heat and work exchanges cancel out to maintain this.
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An isothermal process occurs at:
Explanation: Isothermal processes maintain constant temperature, with heat and work balancing energy changes. Other properties like pressure or volume may vary, unlike isobaric or isochoric processes.
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