New answers tagged thermodynamics
2
Isn't setting $\Delta G = 0$ akin to enforcing a statement about the spontaneity of the reaction?
Yes, it is. But they stipulate that the reaction is at equilibrium, which tells you that neither the forward nor backward reaction is spontaneous, which is precisely what allows you to assert that $\Delta G = 0$.* In other words, when a system is at equilibrium,...
5
Bonds in a molecule are flexible. Thus, each atom can move in any possible direction in 3D space.
Note that they can't necessarily move any possible distance; indeed, if the molecule is stationary, the atoms may not be able to move much distance at all since, after all, they are bonded to other other atoms. In summmary, each atom can move a limited, non-...
0
In my book,“general chemistry” by Ebbing and Gammon,it is stated that at constant pressure Qp=∆U+P∆V=∆H.
This is correct in the absence of electrical and mechanical work (e.g. the equality breaks down for a battery or a fuel cell doing electrical work, or shaft work heating up the reaction mixture).
How come can q equal ∆H?
You can express the change in ...
3
It seems that in some cases it's the same (that is, $\Delta Q_p=\Delta H$) yet in others they differ.
Heat is an energy transfer, whereas enthalpy is a kind of energy content of a sample. When we want to know the change in enthalpy (e.g. before and after a reaction), we use the "$\Delta$" prefix to indicate that. For heat, which already refers to ...
0
It may be difficult or impossible with a pure substance, but a solid may precipitate from a supercritical fluid when the pressure is decreased and the fluid becomes an ordinary gas.
For instance, in principle a solution of sodium chloride in water could be heated and compressed unto the supercritical range of the water. Under supercritical pressure the water ...
-2
Thermodynamically if you calculate the equilibrium constant the equilibrium quotient depends on number of moles of both reactants as well the number of moles of products that is reaction concentration at the equilibrium.more the free energy of reactants the reaction will proceed in a spontaneous manner the more feasible the reaction . Likewise the more the ...
0
For any solid or liquid phase, if there is available volume above it, there will be a non-zero vapor pressure at equilibrium. The presence of other gases has very little effect on the value of this vapor pressure.
On your phase diagram, the y-axis represents the total external pressure, which can be from a gas phase or mechanical (eg a piston pushing ...
1
If you put frozen water in a vacuum at a temperature below the normal freezing point, water will sublimate until the pressure in the vessel reaches the vapor pressure (which is below 1 atm at that temperature). At this point, water will deposit and sublimate at the same rate
However, if you take the same sample and put it outside, the direction of the ...
1
If a reaction is spontaneous, is decided by ΔG= ΔH-TΔS. The value needs to be negative. The second law of thermodynamics tells us that the entropy of the universe always stays the same or increases. Sometimes, for a chemical reaction with negative ΔG, ΔS is negative, but ΔH is as well, that means that the entropy of the system we are describing decreases. ...
0
[This question was asked long time ago, but it appeared on the list today. Let me give it a shot.]
It would make more sense to compare the eutectic point with the azeotropic point for a heteroazeotrope (not for a typically seen homoazeotrope). You can see the similarity between them in the following two phase diagrams, both showing three phases at the ...
0
As already mentioned by me in the comments, both the approaches are exactly the same.
To explain this point, I would like to find the numerical value of the question posted by you in the comments using both methods.
By Manipulating the Equations:
Given:
$$
\begin{align}
\begin{array}{ c c}
\ce{S + 3/2O2 -> SO3 } & ΔH = \pu{-395 kJ} \\
\ce{2SO2 + ...
3
Those are not Coupled reactions; the burning of carbon simply supplies the energy to decompose the carbonate. Another way of looking at it would be if you were the fireman on an old steam locomotive would you prefer to shovel pure coal or a mix of coal and limestone into the firebox for several hours trying to keep the train on time. The reactions are ...
2
This is the complete question at the GenChem 2 level (found posted on Chegg):
The correct answer is C. Of course, there is a relationship between most concepts, but not one where the speed of a reaction would reliably predict the sign of the standard Gibbs energy. Also, fast reactions is a fuzzy concept. A given reaction will be faster or slower depending ...
1
I worked as a production manager for a company that manufactured similar units. On these absorption units, the inside temperature is directly related to the ambient temperature. The warmer it’s outside, the warmer inside. Good ventilation over the condenser to get rid of heat does help and will make a difference. As long as you don’t disturb the natural ...
1
It is well-known that “Solids do not react together at room temperature over normal time scales and it is necessary to heat them to much higher temperatures, often to 1000 to 1500 °C, in order for the reaction to occur at an appreciable rate.” Ref 1. One reason this is true is that even when molecules of one solid diffuse into another solid, the resultant is ...
7
You are unclear if you are confused by $n$ itself, or by the particular notation $n(\ce{Na2CO3})$
$n$ is widely accepted to denote amount of substance, expressed in moles, as @Loong , IUPAC and Wikipedia say.
If $n$ means the amount of the particular substance like $\ce{He}$ or $\ce{H2O}$, it is often written in index form like $n_{\ce{He}}$ or $n_{\ce{H2O}}$...
13
Yes, the standardized quantity symbol according to ISO 80000-9:2009 Quantities and units — Part 9: Physical chemistry and molecular physics as well as the recommended quantity symbol according to IUPAC Quantities, Units and Symbols in Physical Chemistry (Green Book) for amount of substance is $n$.
The quantity “amount of substance” shall not be called “...
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