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.
2,314
questions
0
votes
0answers
21 views
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 ...
1
vote
1answer
36 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 ...
8
votes
3answers
733 views
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 ...
-4
votes
0answers
14 views
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?
1
vote
1answer
56 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 ...
-2
votes
0answers
24 views
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 ...
0
votes
0answers
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 $ΔG=0$. ...
-1
votes
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 ...
0
votes
0answers
33 views
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. ...
-2
votes
0answers
22 views
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{...
2
votes
2answers
75 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
votes
1answer
36 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 ...
4
votes
1answer
32 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 $\pu{298K}$):
$$
\begin{array}{lrrr}
\hline
\text{Substance} & T_\mathrm b/\pu{K} & S^⦵_\mathrm{cal}/R & S^⦵_\...
0
votes
0answers
53 views
Complex formation in water and Henry's law
I've been trying to solve the following problem for a while now.
Consider a mixture of two different gases ($A$ and $B$) for which Henry's law holds. When gas molecules $A$ and $B$ do not interact ...
0
votes
0answers
29 views
Is considering HVO3 + n ROH = HVO3(ROH)n as an endothermic reaction logical?
Here is an article on vanadium solvent extraction with 2-ethyl-1-hexanol: Separation and Purification Technology 2017, 188, 358-366 The suggested extraction reaction is HVO3 + n ROH = HVO3(ROH)n, ...
0
votes
0answers
28 views
Equilibrium in Gas Phase and Pressure
In one task/example there is gas phase reaction and it is said that reaction takes place at pressure of 1 bar and standard Gibbs energy of reaction is needed to be calculated. In this task 1 bar is ...
-1
votes
1answer
38 views
Change in Enthalpy when Pressure is constant
Okay so let me start from the beginning.
I know that $ΔH= ΔU + p ΔV$ ( at constant pressure).
Expanding $ΔU$,
$$ΔH= q + pΔV + pΔV ~~~~~\text{(q at constant pressure)} \tag{1}$$
Next my chemistry ...
1
vote
1answer
59 views
Effect of impurities on melting and boiling points
I am tutoring my nephew for his science GCSEs; and his chemistry textbook states that you can tell how pure any compound is by how close its melting and boiling points are to the "official" ...
1
vote
1answer
46 views
Why are calcination and roasting processes carried out at a temperature just below the ore's fusion temperature?
I had read about the two important methods used for the concentration of an ore - Roasting and Calcination. I have a doubt regarding why both the methods are carried out at temperatures not above the ...
1
vote
1answer
41 views
Why is Enthalpy of Compound at Some Temperature Equal to its Enthalpy of Formation at the Same Temperature?
This is a question I don't understand in thermo. Enthalpy of compound would be sum of U + PV at some temperature, but since we can't calculate absolute value of H, we calculate it relatively to some ...
1
vote
0answers
20 views
If a metal's solvent extraction process is exothermic, then the stripping is necessarily endothermic?
I checked some articles, including Hydrometallurgy 2012, 133-144, 185-191 and Hydrometallurgy 2000, 57, 269-275. In all research papers I checked, an exothermic stripping process followed an ...
1
vote
0answers
24 views
Calculating specific heat capacity from entropy
I'm currently struggling with a specific thermodynamics problem.
I'm given the entropy of a system (where A is a constant with fitting physical units): $$S(U,V,N)=A(UVN)^{1/3}$$
I'm asked to calculate ...
3
votes
0answers
40 views
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 ...
0
votes
2answers
46 views
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 ...
0
votes
0answers
16 views
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?
0
votes
0answers
24 views
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 ...
3
votes
0answers
31 views
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 ...
2
votes
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 ...
0
votes
1answer
29 views
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 ...
1
vote
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 ...
1
vote
0answers
21 views
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.
0
votes
1answer
43 views
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, ...
1
vote
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 ...
-1
votes
0answers
18 views
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 ...
1
vote
1answer
99 views
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 ...
0
votes
0answers
20 views
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 )...
1
vote
0answers
52 views
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 ...
-2
votes
0answers
37 views
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 ...
0
votes
0answers
27 views
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 ...
0
votes
0answers
22 views
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 ...
15
votes
6answers
3k views
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 ...
-2
votes
0answers
37 views
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 ...
-1
votes
0answers
19 views
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 ...
-1
votes
0answers
19 views
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 ...
-1
votes
0answers
26 views
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 ...
-2
votes
0answers
22 views
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 $\...
6
votes
3answers
1k views
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 ...
-1
votes
0answers
21 views
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 ...
1
vote
0answers
34 views
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 ...
1
vote
0answers
22 views
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 ...
