Introduction to thermodynamics and basic terminologies use in thermodynamics

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By: Salman Jaleel
University of Engineering and
Technology Peshawar

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•Thermodynamic
•The branch of science which deals
with the relationship of heat & work
•Heat and work are two mutually
convertible form of energy, it basis
of first of thermodynamic.

3.  A heat engine cannot convert all heat
energy to mechanical work but some
heat will be release at lower temperature
it is second law of thermodynamic.
 HEAT :
 Heat is a form of energy which
transferred from one body to another
due difference in temperature.
 It is the total K.E energy of a body.
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4.  It is denoted by H.
 Consider two bodies A=20C B=22C
 Heat will flows from B to A due to
change in temperature until the
temperature of both become same.
 Due to flow of heat intrinsic energy will
change.
 Intrinsic energy is the total energy of the
substance when it is in rest.
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5.  SYSTEM :
 Any part of matter which is under
considration is called system.
 For example we have a sample in a test
tube, this is our system.
 We have two types of system.
 Close system: A system in which there is no
transfer of mass but energy can be transfer
from surrounding to system.
 Open system: A system in which there is
transfer of mass & heat from surrounding is
called open system.
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6.  The area outside of the system is called
surrounding.
 The real or imaginary line which separating
system and surrounding is called boundary.
 Work :
 work is the product of force and
displacement covered in the direction force.
 W=F.d
W=Fdcosα
 The unit of work is joule.
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7.  1J=N m=Kgm2/s2
 Work and heat are form of energy which
are transitory.
 For example a close cylinder which is
compressed by moving piston down so
temperature & pressure will increase
due to which intrinsic energy of the
system will increase.
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8.  Consider an other example in which a gas is
enclose in a well-lagged cylinder, when heat
is supplied to the system no work will be
done but the intrinsic energy of the will
increase.
 Convention: Usually we denote work
positive when it is done on the system.
 And work will negative when done by the
system.
 Heat will be positive when it is supplied to
the system and it will be negative when it is
rejected by the system.
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9.  Force:
 Force is an agent which tend to produce
motion or stop motion.
 According to Newton law
 F= kma
 but k=1
 so F=ma
 The unit of force is Newton.
 1N=kg/m2
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10.  Energy :
 The ability to do work is to do work is
called energy.
 The unit of energy is joule.
 1J=Nm=kgm2/s2
 There are two main types of energy.
 Kinetic energy : which is due to
motion of a body
 K.E=1/2mv2
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11.  Potential energy: which is due to
the position of the body.
 P.E=mgh
 Power:
 The rate of doing work is called power
 power=work/time
 P=w/t
 The unit of power is watt.
 1W=J/s
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12.  Pressure:
 Force per unit area is called pressure.
 P=F/A
 SI unit of pressure is Pascal.
 1pa=N/m2
 Other units of pressure is atm, bar, torr etc.
 There are three types of pressure
 Atmospheric pressure: It the
pressure on the surface of earth due to the
weight of air. we denote it by atm. The
normal pressure of air is consider as 1atm.
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13.  Gauge pressure: It is the pressure which we
measure with a pressure measuring.
 For gauge pressure we take atmospheric pressure as
zero.
 Absolute pressure: It is the sum of
atmospheric pressure and gauge pressure
 Absolute pressure= atm pressure + gauge pressure
 In absolute pressure we also consider atm pressure
 Gauge pressure will be always positive but absolute
pressure may be negative .
 Negative absolute pressure is called vacuum
pressure.
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14.  Temperature:
 The average K.E of a substance is called
temperature
 For the measurement of temperature we use
such a substance which show expansion and
contraction with change in temperature.
 Mercury is such a substance which show
expansion and contraction with change in
temperature, therefore it is use in thermometer
 There are three scale for measurement of
temperature
 Centigrade, Fahrenheit, Kelvin
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15.  In centigrade scale the M.P of water is
0c and B.P is 100c, the space between 0
and 100 is divide into 100 equal parts
and each is 1c.
 In Fahrenheit scale M.P of water is 32F
and B.P is 212F, the space between 32
and 212 is divided into 180 equal parts
and each part is 1F.
 Kelvin scale start from -273c.
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16.  Specific volume:
 The volume occupied by 1kg of a
substance is called specific volume
 specific volume=
mass/volume.
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