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In this essay we will discuss about the first and second laws of thermodynamics.
Essay # 1. Introduction to the Laws of Thermodynamics:
The results of thermodynamics are all contained in certain apparently simple statements, called the laws of thermodynamics. The first law concerns the conservation of energy. It states that energy can be changed in form, but it can neither be created nor destroyed.
This means that if one form of energy is changed to another form, the same total quantity, expressed in energy equivalents, remains after the transformation. This does not mean that also the quality of energy, i.e., the ability to do work, remains the same.
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Take for example a waterfall. The water of the Niagara rivet possesses potential energy. Potential energy is converted to kinetic energy when it is used to set a body in motion. So, when the water of the rivet starts falling, the potential energy is turned into kinetic energy. After that, this kinetic energy of the water is not lost when the water reaches the pool, but is converted into thermal energy.
This is illustrated by the fact that the water at the bottom of the Niagara Falls is one-eighth of a degree Celsius warmer than at the top. But although the loss of the kinetic energy of the falling water is exactly compensated by the increase in the thermal energy of the water, the quality of the energy is altered.
With the random motion of the molecules of the water in the pool, the ability to do work is much less. Consequently, the ability to do work bas diminished. Another example is a rotating wheel. When a brake is applied to such a wheel, the mechanical energy is converted into thermal energy.
So, when work is done against friction, the lost work equals to the heat produced. The reverse however is not possible. It would be very convenient to be able to convert heat into work merely by reversing a process like friction. This is however not possible as is described by the second law of thermodynamics. The second law states that heat cannot completely be transformed into work.
Since the second law defines quality differences between types of energy, it places distinct restrictions on energy conversions. Although high-quality work can always be completely transformed into low-quality heat, this heat can never be fully reconverted into work.
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Besides this, the second law pervades a 100% efficient energy transformation, because some of the high quality energy will be degraded into heat. The warming up of an electric motor when it runs is an example of this.
The economic relevance that thermodynamics brought to light is that man can only use a particular form of energy. The second law tells us that all kinds of energy are gradually transformed into heat, and that this heat becomes so dissipated in the end that man can no longer use it. Energy thus can be divided into available (or free) energy, which can be transformed into work, and unavailable (or bound) energy, which cannot be so transformed.
Although thermodynamics started with the study of the economy of the heat engine, standard economics did not pay much attention to this physics of economic value. Physical and chemical scientists and biologists, however, did realize the relevance of thermodynamics as a basis for the economic process.
Essay # 2. First Law of Thermodynamics:
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The First Law of Thermodynamics simply states that energy can be neither created nor destroyed (conservation of energy). Thus power generation processes and energy sources actually involve conversion of energy from one form to another, rather than creation of energy from nothing.
The 1st Law of Thermodynamics states that energy is neither created nor destroyed, thus the energy of the Universe is a constant. However, energy can certainly be transferred from one part of the universe to another. To work out thermodynamic problems we will need to isolate a certain portion of the universe, the system, from the remainder of the universe, the surroundings.
The energy transfer between different systems can be expressed as:
E1 = E2
where E1 = initial energy
E2 = final energy
The internal energy encompasses:
i. The kinetic energy associated with the motions of the atoms
ii. The potential energy stored in the chemical bonds of the molecules
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iii. The gravitational energy of the system.
The first law is the starting point for the science of thermodynamics and for engineering analysis.
Based on the types of exchange that can take place we will define three types of systems:
i. Isolated systems no exchange of matter or energy.
ii. Closed systems no exchange of matter but some exchange of energy.
iii. Open systems exchange of both matter and energy.
The change in internal energy of a system is equal to the head added to the system minus the work done by the system:
dE = Q-W
where
dE = change in internal energy
Q = heat added to the system
W = work done by the system
1st law does not provide the information of direction of processes and does not determine the final equilibrium state. Intuitively, we know that energy flows from high temperature to low temperature. Thus, the 2nd law is needed to determine the direction of processes.
Enthalpy is the ‘thermodynamic potential’ useful in the chemical thermodynamics of reactions and non-cyclic processes.
Enthalpy is defined by:
H=U + PV
where
H = enthalpy
U – internal energy
P = pressure
V = volume
Enthalpy is then a precisely measurable state variable, since it is defined in terms of three other precisely definable state variables.
Entropy is used to define the unavailable energy in a system. Entropy defines the relative ability of one system to act to another. As things moves toward a lower energy level, where one is less able to act upon the surroundings, the entropy is said to increase. Entropy is connected to the Second Law of Thermodynamics.
For the universe as a whole the entropy is increasing.
Essay # 3. Second Law of Thermodynamics:
“Heat moves from high temperature regions to low temperature regions”. The second law of thermodynamics states that the entropy of an isolated system never decreases, because isolated systems spontaneously evolve towards thermodynamic equilibrium— the state of maximum entropy. Equivalently, perpetual motion machines of the second kind are impossible.
The second law is an empirically validated postulate of thermodynamics, but it can be understood and explained using the underlying quantum statistical mechanics, together with the assumption of low-entropy initial conditions in the distant past (possibly at the beginning of the universe).
In the language of statistical mechanics, entropy is a measure of the number of microscopic configurations corresponding to a macroscopic state. Because equilibrium corresponds to a vastly greater number of microscopic configurations than any non-equilibrium state, it has the maximum entropy, and the second law follows because random chance alone practically guarantees that the system will evolve towards equilibrium.
The second law is thought to be the source of the direction of time. It is an expression of the fact that over time, differences in temperature, pressure, and chemical potential decrease in an isolated non-gravitational physical system, leading eventually to a state of thermodynamic equilibrium.