Thermodynamics: Zeroth Law and Basic Concepts

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?

Absolute zero temperature Signup and view all the answers

What is the work done for a constant volume process?

0 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:

Thermal equilibrium Signup and view all the answers

What is another name for total heat of a substance?

Enthalpy Signup and view all the answers

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

8314 Signup and view all the answers

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

Isometric Signup and view all the answers

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

Pressure and temperature Signup and view all the answers

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

False Signup and view all the answers

A frictionless quasi static process is called a ____________ process.

reversible Signup and view all the answers

Match the following with their characteristics:

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 Signup and view all the answers

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

Temperature Signup and view all the answers

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

Volume Signup and view all the answers

Heat and work are classified as which type of properties?

Path functions Signup and view all the answers

A _________ system is exemplified by a jet engine.

constant-mass Signup and view all the answers

Internal Energy is a function of only pressure.

False Signup and view all the answers

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

Follow Charle's law Signup and view all the answers

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

Heat absorbed and rejected Signup and view all the answers

What is enthalpy?

Internal energy + Pressure volume product 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.

work Signup and view all the answers

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

False Signup and view all the answers

In an isothermal process, the internal energy:

Remains constant Signup and view all the answers

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

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

Which of the following are intensive properties?

Pressure, Specific Enthalpy Signup and view all the answers

Which of the following is NOT an extensive property?

Entropy Signup and view all the answers

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

Work done Signup and view all the answers

Which of the following is the property of a system?

All of the above Signup and view all the answers

What is the latent heat of ice?

335 kJ/kg Signup and view all the answers

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

By unit degree of an unit mass Signup and view all the answers

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

Isolated system Signup and view all the answers

Which of the following is an extensive property?

Heat Capacity 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?

161.50°C Signup and view all the answers

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

Heat and Work (Q and W) Signup and view all the answers

An adiabatic process is always reversible.

False Signup and view all the answers

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

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

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

work per degree per mass Signup and view all the answers

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

all of the above Signup and view all the answers

Heat transfer occurs due to temperature difference.

True 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 ________.

kilo calorie 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)?

Cp < Cv Signup and view all the answers

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

1040°F Signup and view all the answers

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

Heat transfer is constant Signup and view all the answers

What is a quasi-static process?

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

Temperature and pressure of a perfect gas are intensive properties.

False 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(V_2 - V_1) Signup and view all the answers

Match the expansion properties with their correct description:

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

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

Internal energy 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?

1086 K or 813º C Signup and view all the answers

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

Adiabatic index Signup and view all the answers

Which gas among the following has the highest adiabatic index?

Helium Signup and view all the answers

What is 100ºC in Fahrenheit?

212°F Signup and view all the answers

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

absolute zero temperature Signup and view all the answers

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

Change their momentum due to collision with the wall Signup and view all the answers

What are the fixed points for the Celsius temperature scale?

Ice point as 0ºC and steam point as 100ºC 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?

1.0267 kJ/kg K and 0.7467 kJ/kg K 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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Description

Understand the fundamentals of thermodynamics, including the zeroth law and its application in measurement. Also, learn about throttling process and its characteristics.