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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The criterion for spontaneous change $dU_{S,V} \le 0$

Consider a system undergoing a spontaneous change at V = const and S = const. From first law $dU = \delta q_V$ in the absence of addition work (only P-V work). For the second law $dS \ge \frac {\delta ...
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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 ...
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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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In a binary liquid solution of A and B, if A exhibits positive deviation from Raoult's Law then why component B will also exhibit positive deviation? [closed]

Explain how and why is it necessary for component B to exhibit positive deviation from Raoult's Law as well?
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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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if we force a gas to condense by adding pressure, does the temperature increase?

I understand that due to latent heat there is no increase in temperature during phase change because the energy is being used to form or break inter-molecular bonds not increase kinetic energy. What ...
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26 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
50 views

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. ...
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Temperature change of water due to surrounding environment

I am trying to figure out the temperature change of a tank of water that is located in a hot warehouse. Example, tank water is a chilled system maintained at $\pu{68^\circ F}$, warehouse is hot $\pu{...
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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 ...
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1answer
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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 ...
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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 ...
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Is considering HVO3 + n ROH = HVO3(ROH)n as an endothermic reaction logical?

Here is an article on vanadium solvent extraction with 2-ethyl-1-hexanol: Separation and Purification Technology 2017, 188, 358-366 The suggested extraction reaction is HVO3 + n ROH = HVO3(ROH)n, ...
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Equilibrium in Gas Phase and Pressure

In one task/example there is gas phase reaction and it is said that reaction takes place at pressure of 1 bar and standard Gibbs energy of reaction is needed to be calculated. In this task 1 bar is ...
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Change in Enthalpy when Pressure is constant

Okay so let me start from the beginning. I know that $ΔH= ΔU + p ΔV$ ( at constant pressure). Expanding $ΔU$, $$ΔH= q + pΔV + pΔV ~~~~~\text{(q at constant pressure)} \tag{1}$$ Next my chemistry ...
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1answer
59 views

Effect of impurities on melting and boiling points

I am tutoring my nephew for his science GCSEs; and his chemistry textbook states that you can tell how pure any compound is by how close its melting and boiling points are to the "official" ...
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1answer
46 views

Why are calcination and roasting processes carried out at a temperature just below the ore's fusion temperature?

I had read about the two important methods used for the concentration of an ore - Roasting and Calcination. I have a doubt regarding why both the methods are carried out at temperatures not above the ...
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1answer
41 views

Why is Enthalpy of Compound at Some Temperature Equal to its Enthalpy of Formation at the Same Temperature?

This is a question I don't understand in thermo. Enthalpy of compound would be sum of U + PV at some temperature, but since we can't calculate absolute value of H, we calculate it relatively to some ...
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If a metal's solvent extraction process is exothermic, then the stripping is necessarily endothermic?

I checked some articles, including Hydrometallurgy 2012, 133-144, 185-191 and Hydrometallurgy 2000, 57, 269-275. In all research papers I checked, an exothermic stripping process followed an ...
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Calculating specific heat capacity from entropy

I'm currently struggling with a specific thermodynamics problem. I'm given the entropy of a system (where A is a constant with fitting physical units): $$S(U,V,N)=A(UVN)^{1/3}$$ I'm asked to calculate ...
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Practical meaning of omega potential

In statistical thermodynamics, the quantity omega potential is defined and is different for fermions, photons, phonons and other particles. I have been understanding the derivations of omega potential ...
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2answers
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Internal Energy Changes in Adiabatic Reactor

If we consider adiabatic reactor (one which doesn't exchange energy and matter with surroundings) with some reaction in liquid phase, energy balance for such reactor is written as heat of reaction ...
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Does steam from nuclear reactor does work on the system or to the system?

I was doing research on nuclear reactors and was wondering when the steam from the fission pushes the steam turbine does it do work on the system or to the system?
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is electrolysis of water less efficient with warm water? E.g 40, 50, 60… °C

I see there is High-temperature electrolysis which is a whole different animal than room temp electrolysis. I want to know if electrolysis of lukewarm water will behave much differently. My guess is ...
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Why do we want to operate at dew point or bubble point when doing flash calculations?

I'm trying to dimension a flash drum for a separation between water and isobutane. I now the total inlet flow (F), the composition of the inlet flow ($z_1$ for isobutane and $z_2$ for water) and the ...
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2answers
196 views

Only one unique adiabatic path between two states

My Textbook says: Two states A and B can never lie both on a reversible as will as irreversible adiabatic path. There lies only one unique adiabatic path linkage between two states A and B. I don't ...
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1answer
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Why is enthalpy and not heat released by system used while calculating entropy of surroundings?

While finding the sum of change in entropy of the universe and thus defining Gibbs free energy, why is the change in entropy of surrounding the negative of enthalpy of the system divided by the ...
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1answer
86 views

Relation between enthalpy and internal energy for chemical reaction at constant volume

Question The combustion of benzene(l) gives $\ce{CO2(g)}$ and $\ce{H2O(l)}.$ Given that the heat of combustion of benzene at constant volume is $\pu{-3263.9 kJ mol-1}$ at $\pu{25 ^\circ C}$; heat of ...
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Non expansion work in a system

I know that electrical work or surface tension work are examples of non expansion work but is there an example of a system where expansion and non expansion work are taking place simultaneously.
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In an closed adiabatic container, if we carry out an exothermic process, what will happen to the temperature of the system

I know that a closed adiabatic container acts as an isolated system, so I expect the internal energy of the system to be a constant as in an isolated system. But since it is an exothermic reaction, ...
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1answer
51 views

Gibbs Free Energy Spontaneity Criterion Derivation

In Atkins's Physical Chemistry, spontaneity criterion is derived from Clauisius inequality as follows: Firstly, system is initially at the same temperature T as surroundings. When a change in the ...
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How to determine heat of reaction at STP?

I have often wondered how the standard heat of reaction is determined experimentally for an exothermic reaction as the temperature of the reaction mixture can increase significantly from standard ...
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1answer
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Equilibrium composition of methane–water system under given conditions

Calculate the equilibrium composition of a reactive system consisting of an equimolecular mixture of $\ce{CH4}$ and $\ce{H2O}$ at $\pu{900 K}$ and $\pu{1 atm},$ considered to be an ideal mixture of ...
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Is there a particular definition for the partial derivative of internal energy with respect to volume at constant temperature?

If we have specific internal energy $u=u(T,v)$ then the total differential of $u$ is given by $$du(T,v)=\left ( \frac{\partial u}{\partial T} \right )_vdT+\left ( \frac{\partial u}{\partial v} \right )...
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Confusion in thermodynamically and Kinetically controlled reaction

I am confused in following reaction: $\ce{(CH3)2CH-CHO}$ when reacts with conc. $\ce{NaOH}$, will it undergo cannizaro reaction? According to our professor, It can undergo both Cannizzaro as well as ...
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Gibbs Free Energy Change in Non - Spontaneous Process

If we consider non - spontaneous process like electrolysis, gibbs free energy of a closed system at constant temperature and pressure increases. What I am not sure about is how is it possible for ...
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Measuring energy required or generated in gasification

The typical equation used to measure heat is as follows: $q = mcΔT\\ \text{Where, }\\ q = \text{heat} (\pu{J}) \\ m = \text{mass} (\pu{g}) \\ c = \text{specific heat capacity} (\pu{J g^-1 K^-1})\\ ΔT ...
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Is it the solution energy or the reduction potentials (or both) that drives a galvanic cell?

I have received conflicting explanations for why the redox reaction in a galvanic cell occurs. Explanation 1: Some say that it occurs because the anodic metal dissolves more easily than the cathodic ...
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What is the difference between “vapour” and “gas”?

I have read the definition of vapour on Wikipedia, but I don't seem to have a clear idea about the difference between a vapour and a gas. I know what it means when it says, "gas at a temperature ...
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Additivity of Electrochemical Potentials

When studying derivation of galvani potential difference from interphase equilibria it was written for example that electrochemical potential of zinc is equal to sum of electrochemical potentials of ...
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What is hydration radius?

I know that when an ionic compound is dissolved in water, the polar water molecules surround it and energy is released in this process called hydration energy. But what is the meaning of hydration ...
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Which definition of lattice enthalpy is correct?

I have heard two definitions of lattice enthalpy : "Enthalpy change when 1 mole of an ionic lattice is broken into its gaseous constituent ions" "Enthalpy change when 1 mole of an ionic ...
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Why is non-PV work called 'useful work'? [duplicate]

I was studying thermodynamics and I came to know that the decrease in Gibbs Free Energy for a reversible process at constant temperature and pressure is equal to the non- PV work or useful work ...
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Why cannot we calculate lattice enthalpy of an ionic compound directly from its reaction?

Consider the following reaction : $\ce{NaCl(s)} \rightarrow \ce{Na+(g)}+\ce{Cl-(g)}$ Why cannot we calculate the lattice enthalpy ($ΔH_{lattice}$) directly using this reaction. Just take one mole of $\...
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Why is sea salt coarse?

What makes sea salt coarser than other salt? I have tried checking online but no one seems to discuss this. It seems that the grain of sea salt is larger, but I don't understand since the salt is ...
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What is the difference between enthalpy of combustion and standard enthalpy of combustion?

Is there any difference between enthalpy of combustion and standard enthalpy of combustion or are they exactly the same? I am confused. If there is, could you please also give the definitions of each ...
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Is there a mathematical and rigorous way to prove whether a given function is a state function or a path function? [duplicate]

My textbooks have explained why Enthalpy, Entropy, Internal Energy, Gibbs Free Energy are state functions or path functions only intuitively and with examples. But that never fully satisfied me. Is ...
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Calculating absolute internal energy of an ideal gas system [duplicate]

In the following derivation, I just calculated the absolute internal energy of an ideal gas as a function of its temperature. But my teacher said that we can never calculate the absolute internal ...

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