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.
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Cause of reversible reactions in terms of Gibbs free energy
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I recently learned about the standard Gibbs free energy change of reaction, ΔG=ΔH-TΔS, and how its sign indicates whether the conversion of (ALL) reactants and products is spontaneous or not.
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Could freezing water or making jelly interpreted as a carnot cycle? [closed]
This was a question of a homework, but I'm really confused if it really makes sense. All that I read about carnot cycle always involves gases and even if those cases are reversible process how do we ...
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What is 'non-expansion work' and how does ΔG represent the maximum non-expansion work that can be extracted in a reversible process? [duplicate]
I have just learned about Gibbs free energy and how its value indicates the change in entropy of the universe and can thus be used to find the spontaneity of a reaction. However, I found this other ...
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Are spontaneous exothermic reactions spontaneous due to more stable products or to an increase in the entropy of the surroundings?
The lattice formation of an ionic compound from its infinitely separated gaseous ions is spontaneous under standard conditions, but I cannot figure out the 'driving force' behind this.
One way to look ...
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Endothermic Equilibrium reactions [closed]
we are looking for a list of moderate- highly endothermic equilibrium reactions which preferably only involve one particular state of all products and reactants involved. We have asked teachers and ...
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Thermochemistry calculating enthapy of formation of particular product [closed]
[![Question I found somewhere ][1]][1]
[1]: https://i.stack.imgur.com/fEDY4.jpg What I have done is finding out the formation enthapy of H2o(l) which is around -286KJ/mol . Then i though of using this ...
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3answers
156 views
Is it possible to increase the internal energy of an ideal gas in an isothermal process?
Ideal gas is the one in which there are no attractive or repulsive forces acting and hence its internal energy is due to kinetic energy of its molecules. We may then say, for an ideal gas internal ...
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28 views
Metalic taste of water boiled in electric kettle [closed]
Why does the water, boiled in electric kettle, taste metalic ? Do metalic ions go from metalic plate to the water through electricity ?
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1answer
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Do superoxide salts of heavier alkali metals contradict the principle that lattice energy depends inversely on cation-anion distance?
I have a very basic understanding of quantitative lattice energy calculations: I only know that the lattice energy is directly proportional to the product of charges on the ions and inversely ...
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37 views
Entropy change during electrolysis of water
Consider the electrolysis of water reaction:
$$\ce{H_2O -> H_2 + 1/2O_2}$$
At room temperature and atmospheric pressure, the change in enthalpy of this reaction is $\Delta H = \pu{+286 kJ mol-1}$. ...
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Hydrogen permeation from low to high absolute pressure area due to difference in partial pressure?
I need to get help with a question regarding hydrogen permeation which I do not really how to get around.
The statement is as following:
A steel container contains helium gas at high pressure (100 ...
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26 views
Do the differential expressions of second law of thermodynamics imply a smooth increase in entropy? [closed]
Another statement of second law of thermodynamics can be formulated in terms of system properties and not properties + surroundings (isolated system). For a closed system at constant temperature and ...
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1answer
66 views
Effect of addition of inert gas on concentration in an equilibrium [duplicate]
We have the following equilibrium established in a container with movable piston at atmospheric pressure.
$$\ce{N_2 (g) + 3 H2 (g) ⇌ 2NH_3 (g)}$$
Now how does the concentration of the reacting species ...
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3answers
184 views
Why is standard state useful?
In order to calculate the equilibrium constant we must know the value of $\Delta_\mathrm{r}G^{\circ}$ (which is a function of $T$) so we can calculate $K$ as:
$$K = \exp\left(-\frac{\Delta_\mathrm{r}G^...
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2answers
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Will addition of inert gas change the vapour pressure of a liquid?
From this question on Physics SE Thermodynamics of evaporation:
Now imagine the experiment is repeated but instead of vacuum conditions, the water is pressurized with nitrogen at 1 atm. According to ...
3
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1answer
89 views
Does Raoult's law hold for immiscible liquids?
I know that Raoult's law holds true only for a non volatile solute in a volatile solvent mixture wherein the vapour pressure of the solution gets lowered due to the addition of solute.
Now, first of ...
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77 views
How change in potential energy corresponds to change in enthalpy?
So while reading about activation energy , I came across this graph :
Here, change in potential energy of reactant and product is depicted as ${ΔH}$, but at constant pressure and temperature , ...
3
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1answer
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Is ΔG the maximum non expansion work for reversible processes only?
The derivation of $$\mathrm{d}G=\delta w_{non.exp. max.}$$
$$G=H-TS$$
$$ \mathrm{d}G=\mathrm{d}H-T\mathrm{d}S-S\mathrm{d}T$$
$$\mathrm{d}G=\mathrm{d}U+P\mathrm{d}V+V\mathrm{d}P-T\mathrm{d} S-S\mathrm{...
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2answers
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Examples of endothermic reactions occuring spontaneously at constant temperature and pressure [closed]
Typical spontaneous endothermic processes I can think of (e.g. melting of ice, isothermal gas expansion) involve either an initial temperature difference between the system and the surroundings, or ...
2
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0answers
89 views
Error in the IUPAC Gold Book definitions of exergonic, endergonic, exothermic and endothermic?
All definitions in the IUPAC Gold Book refer to standard values:
exergonic reaction (exoergic reaction) [link]
This expression is often applied to a reaction for which the overall
standard Gibbs ...
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1answer
83 views
Why Does Electrical Work Cause Changes in Internal Energy of the System? [closed]
If we look at system at constant temperature and volume which is galvanic cell, first law of thermodynamics states: $$ dU = dQ + dW'$$
Where W' is electrical work exchanged with surroundings and Q is ...
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Thermodynamics Property Tables
Two rigid tanks are connected by a valve. Tank A contains $0.2\ \mathrm{m^3}$ of water at $400\ \mathrm{kPa}$ and $80\ \%$ quality. Tank B contains $0.5\ \mathrm{m^3}$ of water at $200\ \mathrm{kPa}$ ...
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63 views
Regarding Ellingham diagrams
In my textbook, the following information is given about Ellingham diagram:
The interpretation of $\ce{\Delta_rG^\circ}$ is based on ${K}$ ($\ce{\Delta G^\circ = -RTlnK}$). Thus it is presumed that ...
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Heat of combustion at constnat pressure and volume
Given below is a question, after reading which i had a general doubt, this is not a homework question,Heat of combustion of ethanol at constant pressure and at temperature T K is found to be −q. Hence,...
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1answer
70 views
Why is the formation free energy of carbon dioxide almost constant in Ellingham diagrams?
While reading about Ellingham diagram in my textbook, I noticed that for:
$\ce{C_(_s_) + O2_(_g_) -> CO2_(_g_)}$,
the standard Gibbs free energy ($\ce{\Delta_fG^\circ}$) doesn't seem to vary with ...
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0answers
33 views
What Does Electrical Work Represent in Context of Electrochemical Cells?
If cell operates reversibly than change in Gibbs energy of system equals electrical work of the cell. As far as I know electrical work is work done by electric field when charge moves between certain ...
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1answer
54 views
Different statements of second law of thermodynamics
This may sound trivial but I am having a hard time linking different statements of second law. What I get from second law is that heat cannot be completely converted into work and hence efficiency of ...
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1answer
34 views
Does the critical temperature of a gas depend on the amount of the gas taken?
Does the critical temperature of a gas depend on the amount of the gas taken? Or is it independent of it? My book does not specify this point.
I think according to the gas laws, the critical ...
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1answer
40 views
Enthalpy of Reaction and Efficiency of Electrochemical Energy Devices
For electrochemical energy devices such as batteries or fuel cells working reversibly, efficiency is defined as: $$ \eta = \frac {\Delta_rG^⦵} {\Delta_rH^⦵} $$ Since cell operates reversibly Gibbs ...
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22 views
Is there a public database for enthalpy of solution values?
I'm looking for a public database for enthalpy of solution values. The CRC handbook only has selected compounds available. The NIST webbook doesn't appear to have any enthalpy of solution values. Any ...
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55 views
Maximum non-PV work and reversibility at constant temperature and pressure
When we talk about systems at constant temperature and pressure, maximum amount of non-PV work can be extracted if process is carried reversibly and in that case it is equal to change in Gibbs energy ...
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1answer
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Are the derivations on Gibbs free energy consistent with the interpretation of entropy?
User Buck Thorn writes here that
In chemistry we are most often interested in the effect of changes in $T$ or $P$ on $\Delta G$ for some process such as a phase change or chemical reaction which is ...
5
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2answers
129 views
Why does the dissolution of calcium hydroxide have a negative entropy?
We had an experiment on the dissolution of calcium hydroxide and we obtained the experimental entropy value $\pu{-203 J mol^-1 K^-1}$ with a percent error of $26.7\%.$ Doesn't dissolving a solid in a ...
2
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1answer
88 views
When does a piston stop in an irreversible process?
Suppose we have an ideal gas filled inside a container fitted with a piston. The external pressure is equal to internal pressure.
If we suddenly decrease the external pressure, we say that the gas ...
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2answers
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Calculate Specific Heat given initial temp, final temp and equilibrium temp [closed]
I would appreciate if someone could enlighten me on this question.
Question:
A metallic object with a mass of 2 kg at 50ºC is placed in 10 L of water at 20ºC. When the
thermal equilibrium the ...
4
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0answers
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Why is the reverse aldol cleavage of fructose 1,6-bisphosphate highly endergonic under standard conditions?
I have another question similar to this one. I just don't have intuition for why reactions are thermodynamically favorable or unfavorable and I'd like to build it. This time I'd like to ask about ...
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1answer
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What is the difference between bond enthalpy and bond formation enthalpy?
I came across the following while going through my textbook
The standard enthalpy of reaction is related to bond enthalpies of reactants and products in gas phase reactions as: $$\Delta H^{\circ}_r = ...
2
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2answers
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Why is enthalpy change = heat change only for constant pressure?
Please help me, a mathematician doing his elective course on Physical Chemistry, out with this very simple question: why does the relation between enthalpy and heat $$\Delta H = \Delta U + p\,\Delta V ...
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2answers
792 views
Apparent paradox in the formation of ice at room temperature
The formation of ice out of liquid water can be written down like this:
$$\ce{H2O (l) <=> H2O(s)}$$
We can calculate the change in standard Gibbs free energy (per mol substance) in the following ...
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1answer
49 views
Oxidation of sulfur dioxide to trioxide and its decomposition under same condition at higher temperature
I found that $\ce{SO2 + 1/2 O2 -> SO3}$ when catalysed by platinum and heated to $\pu{700 ^\circ C}$. On the other hand I found that $\ce{SO3 -> SO2 + 1/2 O2}$ with same catalysator and ...
13
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4answers
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What is the physical significance of the universal gas constant R?
While studying work done in isothermal processes I was told that the universal gas constant $R$ is the work done by the gas per mole per kelvin. I am sure I am missing something basic but I didn't ...
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1answer
64 views
Hydration vs Dissolution
While revising Thermodynamics and Thermochemistry from revision material published by Arihant publications I encountered the following mentioned statement.
During dissolution, the physical state of ...
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33 views
Standard Gibb's Free energy change, standard state and equilibrium
I just want to confirm if I am right in thinking that:
statement: When a reaction in standard state is in equilibrium, then equilibrium constant K=1
Reason: since in a equilibrium, $Q=K$ and $ΔG=0$. ...
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1answer
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What is the difference between ΔH = ΔU +Δ(PV) and ΔU = q + w? [closed]
Here, ΔH = Enthalpy change, ΔU = Change in internal energy, P = pressure and V = volume.
I know that ΔH(Enthalpy) is heat given/taken to/from system at constant pressure. But I have been practicing ...
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Why isn't entropy dimensionless?
The usual units are J/K, however
the only reason temperature has different units than energy is because we didn't used to know temperature was just the average kinetic energy of atoms/molecules. ...
5
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1answer
152 views
The reaction of Alkyl Halides with sodium nitrite in DMF
How does the reaction of Alkyl Halides with sodium nitrite in DMF proceed?
I was aware of the reaction of alkyl halides with aqueous sodium nitrite which results in the formation of an alkyl nitrite ...
2
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2answers
98 views
Entropy Changes in Electrolytic/Galvanic Cell?
One of the most fundamental equations in chemical thermodynamics states: $$ \Delta_rH_m^⦵ = \Delta_rG_m^⦵ + T\Delta_rS_m^⦵ $$
If we look at this equation in context of net chemical reaction in ...
2
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1answer
46 views
Enthalpy in the van't Hoff equation
In the van't Hoff equation, why do we say that the change in enthalpy at standard pressure is constant? My book derives the equation for a mixture of ideal gases reacting with each other. The proof ...
5
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1answer
38 views
Why is the spectroscopic entropy of carbon monooxide higher than that of nitrogen?
While solving a question set, I found a question with this data table (at $\pu{298K}$):
$$
\begin{array}{lrrr}
\hline
\text{Substance} & T_\mathrm b/\pu{K} & S^⦵_\mathrm{cal}/R & S^⦵_\...
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Complex formation in water and Henry's law
I've been trying to solve the following problem for a while now.
Consider a mixture of two different gases ($A$ and $B$) for which Henry's law holds. When gas molecules $A$ and $B$ do not interact ...
