Questions tagged [thermodynamics]
Applicable to questions about heat, energy, work, and their interconversion in chemistry. See the tag wiki for a detailed list of topics. Questions tagged may also be tagged with [enthalpy], [energy], [free-energy] where appropriate.
1,574 questions
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0answers
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How do you use the Nernst equation on lithium ion batteries [on hold]
Anode: LiC6<=> C6 + Li+ + 1e-
Cathode: Li+ + 1e- + CoO2 <=> LiCoO2
Overall: LiC6+CoO2<=>C6+LiCoO2
How do you apply the Nernst equation to this reaction? The concentration of solids is ...
-2
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0answers
33 views
Safe liquid with a boiling point > 275F
Is there a non toxic inexpensive liquid which can be safely heated to 275F without worry of it combusting? It would be used to apply heat to PVC to soften it for forming. Perhaps propolyne glycol?
0
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0answers
22 views
What drives the formation of salts?
Can someone explain why potassium and chlorine undergo an exothermic reactiom to form an ionic solid despite that potassium has an ionisation energy of 425 kJ mol-1 and chlorine has an electron ...
0
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2answers
52 views
Flow rate of the fuel consisting of ethanol and water burning in air of a given flow rate
I hope that someone could give me some hints or tips on how to approach this question, even though these types of questions are usually closed off as homework.
A burner is run by a fuel mixture of $...
0
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0answers
29 views
Is it possible to convert a combustion reaction directly into an electrochemical one?
I'm fairly inexperienced in chemistry so forgive me if this question is silly but, why is it not possible to convert a combustion reaction to an electrochemical one directly and harvest the electrical ...
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1answer
21 views
Are enzymes required for reaction coupling? [closed]
In order to couple energetically unfavorable reactions to energetically favorable reactions is an enzyme required?
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0answers
15 views
Does coupling an endergonic reaction to an exgeronic reaction require an enzyme? [on hold]
If the reaction A+B->E is composed of the intermediate reactions A+B->C (ΔG=-20) and C+D->E (ΔG=10). In order for A+B->E to spontaneously proceed is an enzyme necessary to couple the intermediate ...
1
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1answer
32 views
Why are catabolic reactions exergonic and anabolic reactions endergonic?
Catabolism breaks apart large molecules and anabolism creates large molecules. Catabolism is supposed to be exergonic, while anabolism is supposed to be energonic. Id on't really understand this.
By ...
1
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2answers
49 views
Why are reversible reactions spontaneous?
If a reversible chemical reaction is spontaneous in one direction, shouldn't it be non spontaneous $(ΔG > 0)$ in the other? In other words for the reaction:
$$\ce{A + B ⇌ C + D}$$
if
$$\ce{A + B ...
9
votes
0answers
48 views
Explanation of the strength of phosphorus-oxygen bond
When discussing the Wittig reaction, Clayden's Organic Chemistry cites the strength of the $\ce{P=O}$ formed in triphenylphosphine oxide as a driver of the reaction through enthalpy:
The $\ce{P=O}$ ...
0
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2answers
47 views
Exact meaning of constant volume heat capacity
From Wikipedia:
$$
\left(\frac{\partial U}{\partial T}\right)_V = \left(\frac{\partial Q}{\partial T}\right)_V = C_V,
$$
$C_V$ is what known to be constant volume heat capacity. I don't really get ...
1
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1answer
44 views
Is delta S the same in reversible and irreversible processes?
I've read that change in entropy of a system is the same for a system in reversible and irreversible processes since it is a state function and does not depend on the pathway. Does this only apply to ...
0
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1answer
28 views
Inexact differential-path function
From Wikipedia:
an inexact differential cannot be expressed in terms of its antiderivative for the purpose of integral calculations
What's the mathematical reason that inexact differential cannot ...
0
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0answers
27 views
Confusion in change in enthalpy relation
In the equation $∆H=∆U+∆PV$, under what circumstances can we simplify it into $∆H=∆U+P∆V+V∆P$ by product rule?
In this article it mentions that it isn't true. In one question I got a wrong answer ...
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1answer
34 views
As dQ=nCdT, why not dQ is zero in isothermal process? [closed]
Explain in detail about the terms used in first law.
0
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1answer
36 views
When an inert gas is added to a system of constant volume, equilibrium is not effected?
But pressure of the system increases. Because of this increase in pressure, wouldn't (according to Le Chatelier's principal) equilibrium shift towards the side with less moles of gas?
0
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1answer
55 views
Thermodynamics(Calculating enthalpy change)
I know this question would be closed citing it to be a homework question. I posted it earlier also. But believe me I have tried it for myself before and that too many times but then couldn't arrive at ...
0
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1answer
75 views
Reversible and irreversible cyclic processes
The answer in Arihant's book is given as (b), but wouldn't (c) be correct as well? This is a question of IIT JAM Chemistry.
A system undergoes two cyclic processes 1 and 2. Process 1 is reversible ...
1
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1answer
34 views
How do you calculate the delta H for multiple reactions?
I am having difficulty in a question:
Given that
1. $\ce{N_2(g) \rightarrow 2N(g), \Delta H = 941 kJ/mol}$
2. $\ce{N_2(g) \rightarrow N_2^+ + e^-, \Delta H = 1501 kJ/mol}$
3. $\ce{N(...
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1answer
50 views
NaOH or lye. Would it work to remove ice snow or water from a paved surface? [closed]
Thinking of ways to clear ice using chemical reaction.
1
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2answers
55 views
Thermodynamics of a spontaneous isothermal chemical reaction.
Which of the following is/are correct for spontaneous isothermal
chemical reaction?
(A) $\Delta H = 0$, because $\Delta T = 0$
(B) $\Delta S = 0$
(C) $\Delta U = 0$, because $\Delta ...
1
vote
2answers
39 views
When to use internal energy and enthalpy in balances
I am confused as to when you use ΔU and when to use ΔH, I don’t really understand the difference. Is it that ΔU is used for closed systems whilst ΔH is used for open systems?
1
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0answers
36 views
Constraints on rate coefficients in chiral catalytic system
Consider some reversible chemical reaction in a closed system:
$$\ce{A <=> B + D} \tag{1}$$
where $\ce{A}$ is some input reagent and $\ce{B}$, $\ce{D}$ are some output reagents. Let's denote ...
1
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1answer
45 views
Oxygen Solubility in Water
This is probably really obvious, but I really don't understand. Why does oxygen dissolve in water when oxygen is a nonpolar molecule and water is a polar molecule? It's obvious that oxygen does ...
0
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1answer
29 views
Is the water in an aqueous solution undergoing a reaction considered part of the system or surroundings?
System: In chemistry, a system is a chemical reaction. A system operates within its surroundings. Energy can move between the two.
Surroundings: The environment around a particular chemical reaction....
1
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0answers
32 views
Experimental measurement on the ring-strain
for my thesis i calculated the ring-strain of a molecule by MP2 on the computer. I was wondering if there is an easy possibility to get the experimental value of the ring strain. I guess I have to ...
0
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2answers
94 views
If the heat exchanged is different for reversible and irreversible processes, how can enthalpy be a state function?
From the definition of Gibbs free energy, we can write for an irreversible process:
$dG=dH-TdS<0$
With $TdS=\pu{q_{rev}//T}$ this becomes:
$dH-dq_{rev}<0$
Since G is defined for constant (p,...
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votes
0answers
28 views
In bomb calorimetry, why can't we just use the heat capacity of water for the calculation?
The reaction is being carried out in water right? I don't understand why you need to use a different heat capacity for the bomb calorimeter.
0
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1answer
25 views
How to derive the molar fundamental relation
We have the fundamental relation:
$$dS = \frac{1}{T}dU+\frac{P}{T}dV-\frac{\mu}{T}dN$$
how do we get now the following:
$$ds = \frac{1}{T}du+\frac{P}{T}dv$$ where $s = \frac{S}{N}, u = \frac{U}{N}, v ...
3
votes
0answers
39 views
Why does standard reduction potential get multiplied by the change in oxidation state and not by the number of electrons transferred?
The whole basis of Frost diagrams is to have a graphical representation of the Gibbs free energy of formation ($\Delta{G}_{f}$) of different oxidation states of an element using the proportional ...
1
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1answer
31 views
Why does Carnot Engine have the curves as isothermal and adiabatic? [closed]
Why exactly does the Carnot engine have two isothermal and two adiabatic curves? (My book says that “a process is quasi-static if the temperature difference between the system and the reservoir is ...
0
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1answer
53 views
Why does Gibbs free energy correspond sololey to non-expansion work?
First of all: I know this question has been asked before (Why does the Gibbs free energy only correspond to non-expansion work?), and although I understand the mathematical derivation given there, I ...
1
vote
0answers
27 views
Reference conditions for balances on nonreactive processes
In one of the examples in my book (Elementary Priniciples of Chemical Processes) where I am asked to calculate the rate of heat input required to heat a stream of methane and air from 20°C to 300°C, ...
5
votes
1answer
97 views
+50
Using thermodynamics to predict the acid-base character of fluoride ion in water
I was working through the end-of-chapter exercises of the acid-base chapter in Shriver's Inorganic Chemistry when I came across the following problem:
4.7. The effective proton affinity $\ce{A^{'}_{...
0
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1answer
68 views
Getting the pressure of a system by series expansion
An average number, $N$, of bosons of spin $S = 0$ is conned to a two-dimensional domain
with surface $A$. The gas is ultrarelativistic with a single particle energy $\epsilon = cp$, where $c$ is the ...
1
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0answers
27 views
Manganese (II) oxidation by air
I am studying the reaction of dissolved dioxygen with manganese(II) hydroxide for the Winkler method:
2Mn(OH)2(s)+O2(aq)⟶2MnO2(s)+2H2O(l)
The ...
1
vote
2answers
147 views
How to derive the relation between gibbs energy and equilibrium constant?
I want to understand the derivation between gibbs energy and equillibrium constant $$\Delta G=\Delta G^o+RT\ln Q?$$
I have seen a similar post on CSE Derivation of relationship between equilibrium ...
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0answers
36 views
Why HF hydrogen bond become stronger in gas phase than liquid phase?
I found that $\Delta S_\mathrm{vap}$ of HF(similar as the ratio of the molar heat of vaporization of a liquid to its boiling point) is smaller than $90\ \mathrm{J\ K^{-1}\ mol^{-1}}$ which came from ...
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votes
1answer
28 views
How does the theory of thermodynamics account for warm water freezing before cool water?
According to typical sources on thermodynamics, the warmer a liquid is, the longer it will take to freeze it.
For example, I recently was reading a book on refrigeration and this book specifically ...
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0answers
30 views
How to calculate relations among thermodynamic quantities
I'm trying to learn how to calculate the many relations that exist in thermodynamic. Like for example
$$ \left(\frac{\partial U}{\partial S}\right)_V $$ or $$ \left(\frac{\partial S}{\partial T}\...
0
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1answer
54 views
Interpretation of H as T goes to absolute zero
Euler's identity for the enthalpy states that (for a single component and phase)
$ H = TS + \mu N$
What are the implications of this expression in the context of the third law of thermodynamics (...
4
votes
3answers
102 views
Is there a thermodynamic driving force for racemisation?
Why does racemisation occur?
My doubts are:
Is it due to entropy?
If it is due to entropy, how is the reduction of optical activity by racemisation a consequence of increased thermodynamic ...
1
vote
1answer
115 views
Why do we use pV term independent of U in the equation H = U + pV? [duplicate]
I have read the following definition of enthalpy in my textbook:
A substance has to occupy some space in its surroundings depending upon its volume ($V$). It does against the compressing influence ...
0
votes
1answer
40 views
Why is the equilibrium constant being calculated differently here?
In my NMR textbook, it says the equilibrium constant for a dynamic process (e.g., A in equilibrium with B) is calculated by the concentration of A divided by the concentration of B. Is this a typo? ...
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1answer
69 views
Are specific heat capacity and boiling point of a substance related or proportional to each other?
That is, if the substance has a high specific heat, will it also have a high boiling point? ( and vice versa)
1
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0answers
42 views
Expression for the entropy of an ideal gas
I want to obtain the Sackur-Tetrode expression for the entropy of an ideal gas based on:
$$S = K_B ln \Omega$$
We have an isolated system with a fixed volume V and fixed number of particles
N and ...
0
votes
1answer
80 views
What is the substance with the highest specific heat?
I always learned that water has the highest specific heat, but I recently saw that Hydrogen has a specific heat as high as 14 cal/gC and helium has a specific heat of 5 cal/gC, which would be much ...
2
votes
1answer
70 views
Understanding the partial derivative of temperature with respect to thermodynamic beta (coldness)
I am trying to prove that the specific heat is related to the fluctuations in the energy:
$$c_V = \frac{\langle E^2 \rangle - \langle E \rangle^2}{k_\mathrm BT^2}$$
Where:
$$\beta = \frac{1}{k_\...
1
vote
1answer
35 views
In chemistry what do they mean by disorder when in the context of entropy?
Entropy is often the amount of disorder is present in a system, but when they refer it to the degree of disorder in a system what do they mean. It just seems the term is quite vague and not very ...
1
vote
2answers
37 views
What is the reason behind electron transition in the flame test
I am a beginner in this topic but I am aware that when flame test (for alkali and alkaline earth metals) is done there is a s-s transition of electrons from the ground to their excited state.
But I ...
