Questions tagged [entropy]
For questions about the thermodynamical state function entropy, commonly understood as a measure of disorder.
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Why do reactions reach equilibrium?
If the forward reaction causes an increase in entropy then the backwards reaction causes a decrease in entropy, so the backwards reaction is non-spontaneous. If so, then why does the backwards ...
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Is enthalpy of activation the same as activation energy? Is there a purely mathematical way to find that value?
I asked about the effect of pressure on a reaction, and since then I learned a lot more. One of the things I learned was the Eyring equation:
$$\kappa = \frac{\kappa_B T}{h} e^\frac{\Delta^\ddagger S°...
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The road to solvation
To understand the behavior of solubility, it is helpful to look at the chemicals that misbehave, and apply the rules, and look for underlying explanations and common threads. Generally speaking, the ...
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Entropy change of a rubber band
When I stretch a rubber band, the fibers straighten out causing lesser randomness and more order. This should imply the entropy of the rubber band has decreased, but how does the entropy of the whole ...
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Why does more heat transfer take place in a reversible process than in a irreversible process?
We have defined $$\mathrm dS=\frac{\delta Q_\text{reversible}}{T}$$
and the second law of thermodynamics (Clausius inequality) says
$$\mathrm dS\geq\frac{\delta Q}{T}$$
(Here $\delta Q$ is just the ...
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Work and entropy
I am not able to conceive why work wouldn't increase the entropy of a system. If i am compressing a ideal gas adiabatically and reversibly, the gas pressure inside would increase,meaning more no of ...
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Why does entropy increase when the difference in temperatures is decreased?
From the Wikipedia article about Entropy (Source view via The Internet Archive):
In irreversible heat transfer, heat energy is irreversibly transferred from the higher temperature system to the lower ...
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Is ΔS of a system related to temperature and change in enthalpy?
I often see the equation $\Delta S_\text{universe}$ = $\Delta S_\text{surroundings}$ + $\Delta S_\text{system}$, where $\Delta S_\text{surroundings}$ can be re-expressed in terms of the enthalpy ...
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What is at 298 K at standard entropy?
The standard entropy of a substance is the entropy of $1$ mol at $298$K and $1$ bar pressure.
What exactly is at $298$K? The system or the surrounding?
Let's take vapour as an example where $ \ \ce{...
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Entropy Change of Resistor
A very large swimming pool filled with water of temperature equal to $20\ \mathrm{^\circ C}$ is heated
by a resistor with a heating power of $500\ \mathrm{W}$ for $20$ minutes. Assuming the water in ...
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Second law of thermodynamics: How do entropy changes in the system and the environment count in? [closed]
$$\frac{q_{rev}}{T} = \Delta S$$
Here, what does $\Delta S$ signify? Does it mean the change in entropy of the system or the surroundings?
How are the entropies of the system, the surroundings, and ...
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How can a nonspontaneous reaction occur?
$$\frac{-\Delta G}{T}=\Delta S_{universe}$$
(This equation applies under isobaric and isothermal conditions.)
I understand that if $\Delta G$ is positive, the reaction is nonspontaneous, and adding ...
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Can one predict the entropy change for aqueous phase reactions without calculation?
I have seen several sources that claim aqueous solutions always have more entropy than pure liquids or solids, however, some aqueous ions have negative standard entropy. This opens the possibility of ...
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Intuition on Gibbs Free Energy
In many places, I read that Gibbs Free Energy is called "free energy" because some of the enthalpy that comes from the chemical reaction becomes "waste heat" due to a change in the entropy of the ...
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Entropy and enthalpy of hydrogen ion?
The absolute entropy of $\ce{H^+ (g)}$ is $\ce{108 kJ/mol.K}$. However, the absolute entropy of $\ce{H^+ (aq)}$ is exactly 0. Why is that? Also, the standard enthalpy of $\ce{H^+ (aq)}$ is 0, so ...
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Finding value of equilibrium constant
I tried to find the value of equilibrium constant several times.
I failed..
the value of equilibrium constant at 500K
has enthalpy 250kJ/mol and entropy 48J/mol*K
the answer is $ 2.45*10^{-24} $
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Entropy and Heat Capacity Trend in water
It is my understanding that entropy and heat capacity essentially measure the same thing. Since entropy is the ratio of heat (translational, rotational, vibrational movement) to temperature (...
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If chemical reactions occur because everything tends to a lower energy state, why is there such a thing as equilibrium? [duplicate]
It just doesn't make any sense, if a reaction occurs because the reactants go into a lower energy state, then there should be no such thing as equilibrium. right? Because that would mean that the ...
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Gibbs Free Energy and Entropy
I understand Enthalpy, the exchange of energy between products and reactants. But what is Gibbs Free Energy and Entropy? I know that Gibbs free Energy is the difference between the change in Enthalpy -...
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Why is the change in entropy is different for different interpretations?
Forgive me if the title is a bit vague. Read on and I'll clarify.
So, today in class, my teacher was explaining entropy. He gave various examples explaining how the degree of randomness changes. One ...
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Entropy as "extent of energy dispersal" vs. entropy as defined by the Clausius equation
Currently, the concept of entropy as "energy dispersal" has been proved to be more easy to understand than the concept of "disorder". While the first can be applied successfully to explain the ...
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Energy required to break salt bridges in peptides and proteins
Is there a way to calculate the energy required to break a salt bridge in a peptide or on the exposed surface of a protein in aqueous solution? Is there any useful literature on this topic? I'm ...
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What is an entropic trap?
Can someone explain the concept of entropic traps, or provide good sources to look up? The term is not present in any chemistry books I own, and I cannot find online sources explaining it.
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Calculating entropy change of surroundings
I have seen many similar questions but have not found my answer. Why do we use the actual heat involved in the process to calculate entropy change of surrounding? The only answer I can think of is ...
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Which has maximum entropy
Which state has a higher entropy — the
liquid–gas equilibrium or the gaseous state? I have learned that at equilibrium the entropy is maximised. But I also learned that the gaseous state has the ...
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Thermodynamics entropy and temperature
In thermodynamics, whenever heat is released from the system to the surroundings, temperature of surroundings remains unchanged but entropy increases. But entropy is a function of temperature. How is ...
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Is there a way to experimentally measure entropy?
I've been doing thermodynamic chemistry, and recently focusing on Gibbs Free Energy. Whilst doing calculations using, $$\Delta G = \Delta H - T \Delta S$$ I have been given a table of values for $\...
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Interaction between energy and entropy in highly elastic polymers?
Consider the interaction of energy and entropy in the highly elastic materials of an ideal polymeric network.
Now Gibb's free energy cannot be used directly $\Delta H = \Delta G + T \Delta S$ where $\...
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When is a reaction reversible?
When speaking in thermodynamic terms, when is a reaction reversible?
My attempt: A reaction is reversible when $\Delta\text{S} < 0$, because according to the second law of thermodynamics, "in ...
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How does the mixing of two gases increase entropy?
I have learnt that $\mathrm{d}S = \mathrm{d}Q_\mathrm{rev}/T$, where $Q$ is the heat energy absorbed by the system. Now consider an insulated compartment with two chambers, separated by a valve. Each ...
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When you increase the temperature such that change in Gibb's free energy becomes zero, does Keq = 1 at that temperature?
$$\Delta G = \Delta H - T \Delta S$$
say for example, both $\Delta H$ and $\Delta S$ are positive. So assuming $\Delta H$ and $\Delta S$ do not change or change minimally with temperature, if you ...
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Is it really appropriate to measure entropy change using enthalpy?
One statement by Peter Atkins in his book Elements of Physical Chemistry confused me quite a bit:
If a chemical reaction or phase transition takes place at constant pressure , we can identify $Q$ ...
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Why do some chemical reactions lead to less stable state?
If the universe is always trying to find a more stable energy state, then how do reactions take place that lead to a less stable state e.g. the formation of ammonia from extremely stable diatomic $\ce{...
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Meaning of negative entropy value
I was looking through the thermodynamic data chart at the back of my textbook and found that $\ce{S^{2-}_{(aq)}, F^{-}_{(aq)}, OH^{-}_{(aq)}}$ all have negative entropy values. But according to the ...
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Describing evaporation without entropy -- what about Helmholtz?
I have in mind a rigid, impervious, heat-insulating vessel containing a monatomic liquid and vacuum. The vessel has an insulating forcefield inside, exactly at the surface of the liquid. It can be ...
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Entropy change of surroundings
The entropy change of a system is given by
$$\mathrm dS=\frac{\mathrm dq_\text{rev}}{T}$$
which at constant temperature is
$$\Delta S=\frac{q_\text{rev}}{T}$$
I also learned that the entropy change ...
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Entropy of mixing
$$S=k_\mathrm B\ln\mathit\Omega$$
For the mixing of two types of molecules:
$$\mathit\Omega=\frac{N!}{N_1!N_2!}$$
Therefore, subbing in and using Stirling’s approximation ($\ln{N!}=N\ln N-N$):
$$\...
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Determining pressure of sublimation of iodine
The pressure of sublimation of iodine can theoretically be determined by considering the two hypothetical steps: the sublimation of iodine at $\pu{298 K}$, followed by an isothermal expansion of our ...
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Entropy Change for mixing water at two different temperatures
Assume that the heat capacity of water is independent of the temperature. Calculate the net entropy change when 1 mole of water at 0 degrees Celsius is mixed with 1 mole of water at 100 degrees ...
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Do entropy changes have an equivalent of bond enthalpy?
Is it possible to calculate entropy changes in a way similar to enthalpies from bond enthalpies? For example, to work out the enthalpy change of a reaction you can get the sum of all bonds in the ...
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Calculating Enthalpy Changes at Different Temperatures
To calculate $\Delta H$, the change in enthalpy at $\mathrm{100^\circ C}$ for the reaction below, one needs what addition information?
$$\ce{N2(g) + 3H2(g) -> 2NH3(g)}$$
$\Delta H^\circ = ...
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Misconception? "That gas is heavier so it sinks."
I've heard people say many times that one gas is heavier than the other so the heavier gas sinks. Now this must certainly be true to a certain extent (I think of gas used in WWI that sunk into ...
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Calculating Entropy
Atkin's Physical Chemistry Book; Chapter 3; question 3.3(a):
Question
Calculate $\Delta S$ when the state of $\mathrm{3~mol}$ of perfect gas atoms, for which $C_{p,m}$ = $\frac{5}{2}R$, is changed ...
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How is change in entropy of universe related to the energy released by system that can be used to do work?
What does change in entropy ($\Delta S$) represent ? How does change in entropy of a universe ($\Delta S_{univ}$) give us information about energy available to do work.
I would like to know the ...
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Trying to Understand Entropy
I'm currently looking at Principles of Chemistry by Atkins, and I have a few questions involving entropy. These questions probably arise from my poor understanding of reversible/irreversible processes....
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What is the proper term for lines of constant volume and constant enthalpy on a thermodynamic diagram?
I know an isotherm is a line of constant temperature.
Isobar is a constant pressure line.
Isentrope is a line of constant entropy.
But what do you call a line of constant volume? An Isochore?
And ...
user752
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Can someone explain the equation for entropy?
Here's the equation:
$\Delta S = \frac{\Delta q}{T}$
The confusion I have with this equation lies in the variable for temperature, $T$. Why is the temperature constant in this equation? Why can't ...
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deltaS of a decomposition reaction
Suppose we had the following reaction:
$$\ce{Polymer ($n$~units)_{(aq)} -> Polymer($a$~units)_{(aq)} + Polymer($n-a$~ units)_{(aq)}}$$
Without knowing the specific monomer unit of the polymer, ...
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On adding sugar to water, does the entropy increase or decrease?
This question is a little confusing. According to my teacher, the entropy should decrease, but I think that sugar is crystalline first and later it dissolves, so the randomness increases and so the ...
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Entropy change when liquids at two different temperatures are mixed
Two quantities of water ($M_\mathrm{r}=18$) each of mass $216\ \mathrm{g}$ are mixed together in a
vessel. The temperatures of the two quantities before mixing are $303\ \mathrm{K}$ and $333\ \...
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