mephistolessiveur.info: Thermodynamics & Heat: Entropy
Entropy is a measure of how much energy is not available to do work. is the absolute temperature at which the reversible process takes place. . we are led to make a connection between entropy and the availability of energy to do work. Fundamental thermodynamic relation Second law of thermodynamics – The entropy of an isolated system not in equilibrium will tend to increase over time, approaching a is the energy or heat, and T is the constant temperature. The entropy of the thermodynamic system is a measure of how far as absolute entropy) or as a difference in entropy from some other is that it is "a measure of thermal energy per unit temperature that is.
Building on this work, in Lazare's son Sadi Carnot published Reflections on the Motive Power of Fire which posited that in all heat-engines, whenever " caloric " what is now known as heat falls through a temperature difference, work or motive power can be produced from the actions of its fall from a hot to cold body.
Internal energy - Wikipedia
He made the analogy with that of how water falls in a water wheel. This was an early insight into the second law of thermodynamics.
- Energy and Entropy
- Fundamental thermodynamic relation
- Relationship between dynamical entropy and energy dissipation far from thermodynamic equilibrium.
The first law of thermodynamicsdeduced from the heat-friction experiments of James Joule inexpresses the concept of energy, and its conservation in all processes; the first law, however, is unable to quantify the effects of friction and dissipation.
In the s and s, German physicist Rudolf Clausius objected to the supposition that no change occurs in the working body, and gave this "change" a mathematical interpretation by questioning the nature of the inherent loss of usable heat when work is done, e. In Boltzmann visualized a probabilistic way to measure the entropy of an ensemble of ideal gas particles, in which he defined entropy to be proportional to the natural logarithm of the number of microstates such a gas could occupy.
Henceforth, the essential problem in statistical thermodynamicsi. Definitions and descriptions[ edit ] Any method involving the notion of entropy, the very existence of which depends on the second law of thermodynamics, will doubtless seem to many far-fetched, and may repel beginners as obscure and difficult of comprehension.
Energy & Entropy
Historically, the classical thermodynamics definition developed first. In the classical thermodynamics viewpoint, the system is composed of very large numbers of constituents atoms, molecules and the state of the system is described by the average thermodynamic properties of those constituents; the details of the system's constituents are not directly considered, but their behavior is described by macroscopically averaged properties, e.Thermodynamic entropy definition clarification - Physics - Khan Academy
The early classical definition of the properties of the system assumed equilibrium. The classical thermodynamic definition of entropy has more recently been extended into the area of non-equilibrium thermodynamics.
Later, the thermodynamic properties, including entropy, were given an alternative definition in terms of the statistics of the motions of the microscopic constituents of a system — modeled at first classically, e. Newtonian particles constituting a gas, and later quantum-mechanically photons, phononsspins, etc.
The statistical mechanics description of the behavior of a system is necessary as the definition of the properties of a system using classical thermodynamics becomes an increasingly unreliable method of predicting the final state of a system that is subject to some process.
It's also easy enough in principle to keep the entropy constant you make the change adiabatically and do it very slowly. But generally, in most practical situations, if you try to change one of the other variables you'll also end up changing the energy a bit as well. For example, if you change the volume of a system you do work on it, and that changes the energy. But this is a mere practical issue - it's certainly possible in principle to change the entropy of a system without changing its energy.
Thermodynamics is often thought to be mostly about energy, but when you really get down to it, the role played by energy is no different from that played by any other conserved quantity.
Out of all the extensive quantities, the only really special one is the entropy, since it isn't conserved. So for me, the above rearranged version of the fundamental equation is more fundamental than the "fundamental" one.
Entropy - Wikipedia
Another, somewhat unrelated point is that entropy only increases over time on average. For very small systems there are fluctuations, which mean that the entropy can temporarily decrease all by itself.
It turns out that you can't use this phenomenon to do work, so the result that you can't build a perpetual motion machine isn't affected by this.