In The Name of Allah. Simultaneous Thermal Analysis Thermodynamics. By: Pooria Gill; PhD of Nanobiotechnology Assistant Professor at MAZUMS [email protected] Definition. Thermodynamics is an impressive term that might seem more than just a little intimidating at first.
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A drop of dye placed in a cup of water will eventually result in an evenly colored solution, even if we never stir the liquid.
The dye molecules distribute as evenly as possible throughout the volume of water.
An example of this is the conversion of the energy in gasoline to power an automobile.
Only about 20% of the energy results in motion of the vehicle, while the rest of the energy is lost as heat.
This idea that entropy is always increasing can be a bit confusing.
The second law states that the entropy of the universe must increase with each process.
However, this is not the same as saying the entropy of a system must increase with each process.
The system can become more ordered, but the price is that the surroundings must become much more disordered, so that there is still an overall increase in entropy for the universe.
In the previous section, we discussed that spontaneous reactions always proceed in a direction that will give the products less potential energy, or energy available to do work, than they started with.
This means that in a spontaneous chemical reaction, energy is released, and the products of the reaction have less energy than the original reactants.
For example, here is the reaction when the high energy compound ATP is hydrolyzed to release an inorganic phosphate molecule and energy:
ATP + H2O → ADP + Pi ΔG = -30.5 kJ/mol
Note that when the reaction releases energy, ΔG is negative!
When the reaction is written in reverse, the sign of ΔG changes:
ADP + Pi → ATP + H2O ΔG = +30.5 kJ/mol
Let’s say there is a small store that sells products on one shore of a lake.
Because it’s small, the store owner keeps extra inventory in a warehouse on the other side of the lake.
If the warehouse is full but the store is empty, the boat moves from the warehouse to the store, so that there is more product to sell.
This is similar to a biochemical reaction proceeding in an environment where the reactant-to-product ratio is greater than it is at equilibrium.
In other words, there is too much reactant (stuff at the warehouse), and not enough product (at the store).
The reaction (boat) spontaneously proceeds toward equilibrium, which in this case is "to the right".
On the other hand, if it’s right after Christmas and suddenly there are a lot of returns, there is too much product at the store.
The owner has to send some back to the warehouse. This is similar to a situation where a biochemical reaction is proceeding in an environment where the reactant-to-product ratio is smaller than at equilibrium.
In other words, there is too much product while the warehouse sits empty.
Again, the reaction moves spontaneously towards equilibrium, but in this case, that means the boat goes in the opposite direction, "to the left".
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The partial molar heat capacity functions of (a) barnase (Mw=12.4kDa) and (b) ubiquitin (Mw=8.4 kDa), in solutions with different pH.
The dashed lines represent the partial molar heat capacity of native and unfolded proteins.
Data are adapted from "Privalov PL, Dragan AI. Microcalorimetry of biological macromolecules. Biophys Chem. 2007; 126: 16–24".
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