New answers tagged thermodynamics
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Nontoxic liquid with much lower heat capacity and similar freezing point to water
Here is a list of liquids with a melting point between zero and $\pu{5°C}$ : carvacrol, diethyl fumarate, diethylsufoxide, ethyl salicylate, formamide, salicylaldehyde.
And here is a list of liquids ...
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Magnetic work and the first law of thermodynamics
"Magnetic work" generally refers to work done by a constant-current supply connected to a solenoid. Whether this work is done upon the thermodynamic system of interest depends on whether the ...
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How do you calculate the internal energy of a mixture of real gases?
For an gas mixture of constant composition, you have $$dU=C_vdT-\left(P-T\left(\frac{\partial P}{\partial T}\right)_V\right)dV$$where U is the molar internal energy and V is the molar volume. For a ...
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Calculating the amount of water condensed when cooling below the dew point
The maximum vapor pressure of water is $\pu{4243 Pa}$ at $\pu{30°C}$, and $\pu{872 Pa}$ at $\pu{5°C}$. If the original humidity is $\pu{60}$%, it means that the initial vapor pressure is $\pu{0.600 · ...
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Evaporation of zinc oxide
Your following sentence is wrong (I copy it in italics without change)
1/2O2 is just oxygen gas with charge 1/2O2 = 0.5(-22) = -2
No! There is no charge $-2$ on the oxygen atom in the molecule $\ce{O2}...
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Why does the equation for chemical potential apply to liquids and aqueous solutes?
The kinetic theory of matter says that matter consists of individual particles be they atoms, molecules, ions, nanoparticles, even elephants; the state of aggregation can have an effect. Let's ...
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In regards to the Gibbs free energy equation, it seems that the two terms oppose one another, Enthalpy and -TS. Can you explain this?
At equilibrium deltaG = 0 = deltaH-TdeltaS; deltaH = TdeltaS. This means that a system at equilibrium is stuck there unless matter [chemical potential] or energy is changed to perturb the ...
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At constant temperature, can the solid phase be more stable than the gas if pressure decreases?
That's not really possible. To see why simply express the Gibbs' free energy for each of the phases of the homogeneous substance in differential form:
$$dG = Vdp - SdT$$
We assume constant composition....
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How is reaction enthalpy equal to heat in a coffee cup calorimeter?
First, a remark about notation and dimensions. $\Delta H$ has dimensions of energy. I will use $\Delta_r H$ for the enthalpy of reaction, and it has dimensions of energy per amount of substance. The ...
- 30.3k
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Understanding the molar free energy to simulate phase separations (Na2O-SiO2)
As an extension of the above answer of Jon Custer, I would like to draw attention to the paper of Charles (1967). On page 634 Charles is concerned with a similar unfortunate fact that "the ...
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Why is it necessary for the standard enthalpy of fusion to change at the transition temperature?
It is not the enthalpy change that goes to zero at phase equilibrium, but the free energy change. And that involves entropy as well as enthalpy.
What happens is this: the "higher" phase -- ...
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In regards to the Gibbs free energy equation, it seems that the two terms oppose one another, Enthalpy and -TS. Can you explain this?
It is not about opposing terms but from experimental necessity. In the early days before the second law was understood it was assumed that the most efficient utilisation of chemical energy consisted ...
- 26.7k
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In regards to the Gibbs free energy equation, it seems that the two terms oppose one another, Enthalpy and -TS. Can you explain this?
The combined effect of $ \Delta H-T\Delta S $ is a measure of spontaneity. The individual terms (i.e., $ \Delta H$ and $T\Delta S $) are not the actual measure of spontaneity. But in general we say ...
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Accepted
Does mayer's equation change for two mole of ideal gases or is it remains same for any number of moles
Note that dimension of $R, C_p, C_V$ is $\pu{J K-1 mol-1}$ and not $\pu{J K-1}$.
Molar ($\pu{J K-1 mol-1}$) and specific ($\pu{J K-1 kg-1}$) heat capacities are intensive properties, independent on ...
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How do I turn room temperature water into boiling water for drinking using an chemical/additive?
Don't let the others here discourage you from thinking big. Having said that, the problem with your scheme is that generally we want to avoid adding stuff to drinking water, in order to keep it pure (...
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How do I turn room temperature water into boiling water for drinking using an chemical/additive?
Long shot but if you can engineer a strong enough metal container and isolate the expanding gas' cooling effect from the system, you can maybe just maybe mix HN3 and nitrous acid. Byproducts are a lot ...
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Why is the value of the heat capacity ratio γ the same for molecules with the same atomicity?
If we deal with an ideal gas then $C_p=C_V+R $ then $\gamma=1+R/C_V$ which then begs the question if $C_V$ is different for different molecules why is $\gamma$ constant and the same for molecules with ...
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Accepted
Understanding Cahn-Hilliard Equation in terms of Units
This question is addressed here. For the units, $e$=energy (eg J), $t$=time, $l$=length.
The Cahn-Hilliard equation after the variational derivative takes the form$$\dfrac{\partial c}{\partial t}=V_{...
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Why do different places on Earth have different concentrations of particulate matter in the atmosphere?
Because the atmosphere is not in equilibrium
If the atmosphere were a small closed vessel, it might have a chance of reaching an equilibrium where everything in it would be evenly distributed. But it ...
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What endothermic reactions can be effectively reversed by electrolysis?
Any elemental, i.e. single step, reaction and many more complicated reactions that can reach equilibrium, can be reversed. The forward and reverse reactions in an equilibrium situation follow the same ...
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Why do different places on Earth have different concentrations of particulate matter in the atmosphere?
Particulates are not dissolved in air, but suspended. Gravity operates on them. That said, sand from Africa does reach the Americas.
Also, the atmosphere is not in equilibrium -- there are sources of ...
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