Thermodynamics
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| Discuss Thermodynamics THERMODYNAMICS
What is thermodynamics?
Thermodynamics is the study of laws that govern energy changes (chemical or physical) i.e. the conversion of energy from one form to another, the direction in which the heat will flow, and the availability of energy to do work.
Types of thermodynamical process
ISOTHERMAL PROCESS
A process in which the temperature of the system remains constant although heat may enter or leave the system. Thus in this process DT is zero.
ADIABATIC PROCESS
A process in which no heat enters or leaves the system during the reaction. IN this process DQ is zero.
ISOBARIC PROCESS
The pressure of the system remains constant throughout the reaction during this process. In this process DP is zero.
ISOCHORIC PROCESS
The volume of the system remains constant during this process. For this process DV is zero.
CYCLIC PROCESS
It is a process which comes to its initial state after the reaction through a number of different processes. For this process DH = 0 and DE = 0 .
THERMAL EXPANSION
The increase in the dimensions of a substance, when the temperature is increased is called expansion. It can be broadly divided into three types:
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Linear EXPANSION: When the solid specimen increases in its length only, then the expansion is called linear expansion. The linear expansivity is defined as the fractional increase in the length of the specimen per unit rise in the temperature.
If a specimen increase from length l1 to l2, when the temperature is increased by T then the relation between thermal expansivity a, length and temperature is given as,
l2 = l1(1 + aT)
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SUPERFICIAL EXPANSION: When the solid specimen increases in its surface area only, then the expansion is called superficial expansion. The superficial expansivity is defined as the fractional increase in the area of the specimen per unit rise in the temperature.
If a specimen increase from length A1 to A2, when the temperature is increased by T then the relation between superficial thermal expansivity b, area and temperature is given as,
A2 = A1(1 + bT)
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VOLUME EXPANSION: When the solid specimen increases in its volume, then the expansion is called Volume expansion. The volume expansivity is defined as the fractional increase in the volume of the specimen per unit rise in the temperature.
If a specimen increase from volume V1 to V2, when the temperature is increased by T then the relation between volume thermal expansivity g, volume and temperature is given as,
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V2 = V1(1 + gT) |
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a = b/2 = g/3 |
NOTE: in the case of liquids the expansivity observed directly is called apparent expansivity, as the container also expands as the temperature rises. The absolute expansivity is thus given by apparent expansivity plus the volume expansivity of the container.
NOTE: in the case of gases, expansivity is governed by Charles’s law, which states ” the volume of a fixed mass of a gas at a constant pressure expands by a constant fraction of its volume at 0O centigrade. For ideal gases this fraction is about 1/273. Mathematically, it can be given as,
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V2 = V1 (1+ T/273) |
IDEAL GAS LAWS
These are a set of laws relating the temperature, pressure, and the volume of an ideal gas.
BOYLE’S LAW
This law states that the pressure of a gas is inversely proportional to its volume at constant temperature.
PV = constant
And we can thus state
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P1V1 = P2V2 = P3V3= … |
The volume of a fixed mass of a gas at a constant pressure is directly proportional to the thermodynamic temperature.
V/T = constant
And we can thus state,
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V1 /T1 = V2 /T2 = V3/T3 =… |
The above three equations can be combined in the universal gas equation, which is given by
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PV = nRT |
Where n is the number of moles of the gas n of the specimen and R is the universal gas constant. The value of R is given by, 8.31434 JK-1mol-1.