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.
1,922
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What matters most when attempting to achieve the highest efficiency water electrolysis, voltage, current or resonant frequency?
I recently constructed a rudimentary water electrolyzer using some homemade electrodes and PVC pipe. I have read much about electrolysis and how it works, but I am still left with many questions. I am ...
3
votes
1answer
27 views
Derivation of the isothermal Joule-Thomson coefficient
The definition of the Joule-Thomson effect is:
$\mu=\left(\frac{\partial T}{\partial P}\right)_H$
And this is defined in an isenthalpic process, i.e. $dH=0$.
My book shows the derivation of the ...
2
votes
1answer
29 views
what is the physical significance of ∆H=∆U for a chemical reaction?
In case of few chemical reactions $\Delta n=0$,so according to the equation $\Delta H= \Delta U+\Delta nRT$ change in enthalpy equals change in internal energy. But what does this in essence actually ...
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0answers
17 views
Le Chatliers principle
I need help with following question:
A cooling pad consists of three pockets, the one in the middle consist of water and the other two of a salt. When the pad is pressed hard enough the walls between ...
-1
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0answers
45 views
Does a positive Gibbs energy violate the Second Law of Thermodynamics? [duplicate]
Let's consider a reaction in an isolated system with constant temperature and pressure:
The total entropy change of the system is given by the formula: $\Delta S_{total} = \Delta S_{sys} + \Delta S_{...
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0answers
9 views
Heat exchanger area calculation [closed]
i got this question from my test but i do not know the answer, could someone help me solve this problem please. thank you
0
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1answer
49 views
The amount of heat energy required to raise the temperature of 1g of helium at NTP from T1 K to T2 K is?
The amount of heat energy required to raise the temperature of 1g of helium at NTP from $T_1 \pu{K}$ to $T_2 \pu{K}$ is?
My confusion is, that as the gas is at NTP, therefore, it is an isochoric ...
0
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0answers
28 views
Is there some way to predict the sign of Gibbs free energy of formation of a compound? [closed]
I read that the Gibbs free energy of formation of benzene is around $+100 kJ/mol$. Since the Gibbs free energy of formation is positive, benzene is thermodynamically unstable and has a spontaneous ...
0
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0answers
18 views
Is there any effect on bonds formation and reactants due to a reaction in adiabatic calorimeter
Is there any effect on reactants and bond formation due to a reaction going on a adiabatic calorimeter.We know enthalpy of a reaction should be measured at constant temperature but in adiabatic ...
0
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1answer
38 views
When reactants are in their transition state, can they go back into their reactants form instead of progressing to form the products?
When reactants are in their transition state, can they go back into their reactants form instead of progressing to form the products? I don't see any reason why the reaction has to keep progressing ...
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18 views
What is the effect of pH on tautomerism ( general and wrt imine - enamine tautomerism) [closed]
I presume it's interplay of thermodynamic and kinetic factors where only thermodynamic considerations would suffice. The yield may depend on pH as tautomerism involves abstraction of H.
Note: I am ...
0
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0answers
23 views
Is constant pressure heat capacity = entropy during adiabatic reversible expansion of perfect gas?
For any process, ∆G = ∆H - ∆(TS).
Apply this on reversible adiabatic expansion of perfect gas, since the entropy of system does not change during this process, S is constant so
∆G = ∆H - S∆T
The ...
1
vote
1answer
19 views
How come I get different Gibbs free energy for the same reduced equation?
I want to calculate the Gibbs free energy of this reaction which can be:
$\ce{H2(g) + 1/2O2(g) -> H2O(g)}$
or
$\ce{2H2(g) + O2(g) -> 2H2O(g)}$
I am using the entropy values (J/molK): H2(g) ...
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votes
0answers
40 views
Calculation of Reynold number [closed]
Water stream (density 993.7 kg/m3, viscosity 0.656 mPas) is fed to the shell side of a shell and tube heat exchanger. The inner diameter of the shell is 45 cm, it contains 85 tubes of diameter 25/30 ...
0
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0answers
18 views
Internal energy with microscopic kinetic or potential energy [closed]
For every process in an isolated system that has no macroscopic kinetic or potential energy, ∆E=0
Will this statement be true if instead of macroscopic it were microscopic?
1
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0answers
22 views
thermodynamics problem [closed]
The boiling point of a substance $X$ at 1 atm pressure is $500 k$ . The enthalpy of vapourisation at the boiling point of $X$ (l) is 80 kj/mol .The molar specific heat of $X(l)$ = $5 × 10^{-3}$ kj/mol ...
0
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0answers
36 views
Change in Entropy and Enthalpy found over a temperature range and asked to compute the change in Gibb's Energy
I was given the following question by my tutor:
"The variation of enthalpy ($\Delta H$) and entropy ($\Delta S$) in a reaction carried out at
constant pressure in the temperature range between 300 ºC ...
-2
votes
2answers
33 views
How do you manage to liquefy a gas by applying only pressure? [closed]
How can you liquefy a gas by applying only pressure? To increase the pressure of a gas you need a compressor, and when the compressor does work on the gas , it will increase his pressure but at the ...
1
vote
0answers
17 views
Why is average bond enthalpy measured by homolytic fission?
Average bond enthalpy: the energy required for 1 mole of a specific gaseous bonds to undergo homolytic fission
Why specifically homolytic fission? Is it to allow comparison, but if that were the case,...
3
votes
5answers
410 views
How can we define a non-spontaneous reaction?
Consider a reaction:$$\ce{$aA + bB$ <=> $cC + dD$}$$
The value of reaction quotient at a certain time $t$, $${Q_c = \frac{[C]^c[D]^d}{[A]^a[B]^b}}$$
where the concentrations $[A], [B], [C]$ and ...
1
vote
2answers
43 views
Concentration of gas above aqueous ammonia
I am a physicist who has run into some chemistry in the lab (and unfortunately, I've completely evaded any formal training in chemistry). I have exposed some samples (I think details of the sample are ...
0
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1answer
52 views
Difference between chemical energy and potential energy
I know that chemical energy is the potential energy stored in the arrangement of atoms within molecules. Forming new chemical bonds releases energy.
what does potential energy mean?
Is it the energy ...
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votes
1answer
37 views
Entropy Change In Rusting of Iron [closed]
I presume that the entropy of the system should decrease during rusting of iron because the atmospheric oxygen gets converted to solid state from gaseous state which should result in the decrease of ...
0
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0answers
21 views
Meaning of chemical energy [duplicate]
I am trying to understand the meaning of chemical energy.
I saw in my book that chemical energy is stored in the bonds of chemical compounds and when the bonds are untied the chemical energy increases....
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0answers
35 views
Relation between enthalpy, entropy and Gibbs energy at thermal equilibrium
$${\Delta S_{total} = \Delta S_{sys} + \Delta S_{surr}}$$ ... Equation (i)
If system is in thermal equilibrium with the surrounding i.e. ${T_{sys} = T_{surr} = T}$
Increase/ decrease in enthalpy of ...
0
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0answers
29 views
Change in temperature if salt is dissolved in water with different initial temperatures
I will mix a salt with room-temperature water and 8 degree Celsius water. Then I will compare the heat of solution with each other.
Does the initial temperature of the water affect how much the heat ...
-1
votes
1answer
30 views
Is this example considered liquifying a gas under pressure?
In my work place, we have a drum that has propene inside at a pressure of around 2,5 bar and at a temperature of around -15ºc and the boil-off of that drum is aspirate by a compressor and is ...
0
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0answers
24 views
Combining enthalpies of formation and combustion in the context of Hess's law
I know that you can use enthalpy of combustion to work out formation, and Formation to work out enthalpy change. But can you use enthalpy of formation and combustion data is the same Hess's cycle to ...
15
votes
5answers
2k views
What exactly is temperature?
I've read at many places that temperature is the average kinetic energy of particles present in an object. I just don't intuitively get how kinetic energy is connected with temperature. And how is ...
0
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0answers
17 views
What is the lattice enthalpy of zinc chloride?
I am trying to find a literature value for the enthalpy of solution of zinc chloride to compare with my experimental value but I can't seem to find it. So I'm trying to use the formula: enthalpy of ...
1
vote
2answers
31 views
Why does electrode potential depend upon enthalpy of hydration and sublimation?
It's given in text that "Electrode potential among other things depends upon: enthalpy of sublimation,ionization enthalpy and hydration enthalpy." I could understand why it would depend upon ...
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votes
1answer
32 views
Heat transfer to an ideal gas [closed]
In thermodynamics, why is the heat that is transferred to an ideal gas considered as work that was done on the system for an isothermal process?
0
votes
1answer
76 views
Hyperconjugation, stability of molecules, and heat of formation
I recently asked a question about why the heat of formation of organic radicals and positive ions decreases with their size and degree of branching at the radical or ionic site. The user "Buttonwood" ...
1
vote
1answer
79 views
Why does the heat of formation of organic radicals and positive ions decrease with their size and degree of branching at the radical or ionic site?
I am currently studying the textbook Mass Spectrometry, third edition, by Jürgen H. Gross. Chapter 2.4.3 Bond Dissociation Energies and Heats of Formation says the following:
The heat of formation ...
0
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1answer
53 views
Intermolecular Forces of Attraction [closed]
Imagine a bottle 85% filled with water and the rest is just air, and the cap is closed. Here are now my questions.
Since the cap is closed completely, the air bubble is formed. Is that air bubble ...
1
vote
0answers
41 views
Calculating volume of a vessel using idea gas law [closed]
To an evacuated vessel with movable piston under external pressure of $\pu{1 atm},$ $\ce{0.1 mol}$ of $\ce{He}$ and $\pu{1 mol}$ of unknown compound (vapour pressure $\pu{0.68 atm}$ at $\pu{273 K})$ ...
4
votes
2answers
60 views
Most endothermic room-temperature reaction [closed]
In terms of energy per gram of reactants, the evaporation of water at -2.2 kJ/g, is much higher than any chemical endothermic reaction that I have seen demonstrated. At extreme temperatures there is ...
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0answers
28 views
What is the Gibbs free energy of Lithium-Graphite and Lithium Cobalt-Oxde
I'm trying to do some hand calculations for Lithium-Ion batteries and I can't seem to find the standard state Gibbs free energy of formation for either Lithium-Graphite or Lithium Cobalt-Oxide. They ...
0
votes
1answer
46 views
For bond dissociation energies (BDEs) of double and triple bonds, is number shown in tables for that second or third bond? Or all of them?
Simple, 'dumb' question.... Is the kJ/mol number given in tables of bond strengths or bond dissociation energies , when it comes to double and triple bonds, just for the 'last' bond or for both (or ...
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votes
2answers
68 views
Is irreversible work a path function? [closed]
In $P/V$ plots of irreversible processes only initial and final state is defined due to sudden compression or rarefaction then how is work done a path function in irreversible processes.
Why won't ...
0
votes
1answer
39 views
Mechanistic explanation of salt lowering temperature of ice slush
As we all know, adding salt to ice water lowers its temperature.
I've read plenty of system-level accounts of energy balances, enthalpies, vapor pressures, phase equilibria and freezing points—I ...
1
vote
1answer
51 views
Endothermic or Exothermic [closed]
Is an endothermic reaction always endothermic at all conditions of pressure, temperature etc.? Similarly for exothermic... I mean is sign of ∆H always the same as sign of ∆H°?
This might seem to be a ...
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2answers
78 views
Are there any reactions that are endothermic and exothermic? [closed]
As it says: are there any reactions that require heat and produce heat simultaneously?
2
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2answers
44 views
Is equilibrium constant at a given temperature derived from Gibbs free energy of reaction valid for doing simple kinetic modelling?
I intend to do a kinetic study of simple alcohol catalytic dehydrogenation reactions in the gas phase. I want to start with simple power law kinetics using $K_\mathrm{eq}$ to account for the ...
1
vote
2answers
100 views
Endothermic reaction absorbs heat from environment
I read on my school book about chemistry the reaction:
$$\ce{H2O + NH4Cl}$$
with $T(\ce{H2O}) = \pu{25 °C}.$
The temperature of the final solution is $\pu{20 °C}$.
I know that it is an endothermic ...
1
vote
1answer
57 views
Can someone explain the article below? [closed]
This is the article: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5611670/
I'm not a Chemist, so I can't understand the article very well.
The conclusion states that the molecules tested should not ...
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votes
1answer
59 views
Why does the combustion of graphite have a positive Delta S?
The following reaction is exothermic and entropically favorable:
$$\ce{C (s) + O2 (g) -> CO2 (g)}$$
My question: Why is this reaction entropically favorable?
Clearly there are more ways ...
2
votes
0answers
36 views
Using Maxwell Relations or any other mathematical or thermodynamic relations, prove that (∂Cp/∂P)=−T(∂^2V/∂T^2)
Prove that:
$$\left(\frac{\partial Cp}{\partial P}\right)_T = -T \left(\frac{\partial^2 V}{\partial T^2}\right)_P$$
Since $Cp = (\frac{\partial H}{\partial T})_P$
$$\left(\frac{\partial Cp}{\...
0
votes
0answers
65 views
Why is the equilibrium constant for a Daniell cell not equal 1?
Using the equation
$$RT\ln K = nFE,$$
the equilibrium constant $K$ for a Daniell cell at standard conditions can be found as
$$K = \exp\left(\frac{2 × 96500 × 1.1}{8.3145 × 298.15}\right) = \pu{1....
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votes
1answer
35 views
Batch Process engineering
For a fast chemical reaction where reactant A is fed into an agitated solution of reactant B.
Can the selectivity of the reaction be strongly dependent on the location of the feed pipe outlet?
I am ...
