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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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 ...
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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 ...
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1answer
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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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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 ...
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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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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
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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 ...
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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 ...
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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 ...
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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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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 ...
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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 ...
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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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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 ...
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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?
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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 ...
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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 ...
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2answers
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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 ...
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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,...
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5answers
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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 ...
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2answers
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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 ...
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1answer
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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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1answer
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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 ...
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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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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 ...
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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 ...
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1answer
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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 ...
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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 ...
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5answers
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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 ...
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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 ...
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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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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?
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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" ...
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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 ...
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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 ...
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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 $\pu{273 K})$ ...
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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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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 ...
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1answer
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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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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 ...
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1answer
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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 ...
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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?
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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 ...
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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 ...
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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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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 ...
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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}{\...
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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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1answer
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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 ...

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