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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Gibbs energy of electron transfer
The reaction Gibbs free energy of a cell is
$\Delta_\mathrm{r}G^\circ = -nFE^\circ, \tag{1}$
and the Gibbs energy of photoinduced electron transfer according to IUPAC is
$$\Delta_\mathrm{ET}G^\circ = ...
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Cp=Cv for isochoric processes?
According to the first law of thermodynamics, ∆U = ∆H + work done, where magnitude of work done is given by W = PdV.
In an isochoric process work done would be zero (provided the external pressure ...
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Why is the isenthalpic condition required in the Joule–Thomson effect?
I have been struggling to understand how the molecules behave during the Joule–Thomson effect. I would love to get some help on this concept. Here is what I got so far.
Under adiabatic and isenthalpic ...
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What is the change in enthalpy for constant volume?
Which of the following is the correct equation of enthalpy?
$$
\begin{align}
\Delta H &= \Delta U + \Delta (pV) \tag{1} \\
\Delta H &= \Delta U + p\,\Delta V \tag{2} \\
\Delta H &= \Delta ...
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Calculating concentration quotient and determining direction of reaction for equilibrium involving gases
I'm currently working on a chemistry problem involving chemical equilibrium, and I'm having some trouble figuring out how to calculate the concentration quotient $Q$ and determine the direction in ...
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Exact meaning of constant volume heat capacity
From Wikipedia:
$$
\left(\frac{\partial U}{\partial T}\right)_V = \left(\frac{\partial Q}{\partial T}\right)_V = C_V,
$$
$C_V$ is what known to be constant volume heat capacity. I don't really get ...
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Why aren't Gibbs energies additive in the serial reduction of cupric ion? [closed]
Since Gibbs potential is a state function, it should be additive, regardless of the path chosen to go from a state ($\ce{Cu^{2+}}$) to another ($\ce{Cu}$).
While providing a solution to another ...
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How can entropy of universe or surroundings be a state function?
If a system goes from state A to B in a reversible process, then $(\Delta S)_{\text{universe}}=0$. However, my confusion starts if we take an irreversible route. For the system, even if we take the ...
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Is the activation energy for vaporization equal to the enthalpy of vaporization?
When ethanol, say, evaporates, the intermolecular forces between molecules need to be broken. As a vapour, there are no new forces being created, so it is a purely endothermic process, with no "...
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Why is Charcoal such an excellent adsorbent?
Charcoal (also activated charcoal) is known to adsorb a huge variety of substances including a variety of paints, dyes and many different kinds of ions. Moreover, the amount of adsorption at normal ...
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Which Gibbs' free energy is an activation energy diagram referring to?
In the case of activation energy diagrams in terms of potential energy, I understand that when we're talking about two individual molecules, the potential energy is highest in the transition state ...
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What is Brown's Gas
I've recently heard references to something called "Brown's Gas" which can be used to cut/weld metal but is regarded as 'a cold flame'. Does it actually exist and if so, why is it not widely used?
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Calculating the enthalpy of reaction at non-standard concentration for reactions in aqueous phase
Standard conditions for a chemical reaction in the aqueous phase, for instance, a chemical reaction in solution, consider that reagents should be at a 1 M concentration. I was wondering how to ...
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Reason for negative Joule Thomson coefficient of Helium and Hydrogen at NTP conditions
Recently, while reading my textbook I came to know that Helium, Hydrogen and Neon are the only gases which have negative Joule Thomson coefficient at NTP conditions, i.e heating effect is observed ...
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Can someone help me with the experimental tabulation or spread sheet data on enthalpy, temperature, and pressure for aluminum and oxygen combustion [closed]
I need an experimental tabulation or spread sheet data of enthalpy, temperature, and pressure tabulated in columns for aluminum and oxygen combustion under non standard conditions.
Any references to ...
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What is the meaning of thermodynamic tendency?
While giving a test, I encountered a question which was as follows
Lead reduces $\ce{NO_3^-}$ into $\ce{NO}$ and $\ce{NO_2}$ depending on the concentration of $\ce{HNO_3}$ in solution. Assuming that $...
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Is the enthalpy change of a reversible adiabatic expansion any different from enthalpy change of a irreversible adiabatic expansion?
Some sites say that adiabatic expansions of ideal gases in general have $\triangle H =0$ , whereas some say it is not.
I tried to find $\triangle H$ by considering a reversible adiabatic process where ...
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What would the adiabatic and isothermal curves of a system look like for the same initial and final pressure and volume?
Usually, when I see a graph of reversible adiabatic and isothermal processes it's something like this.
Which makes sense mathematically since
$yx^{\gamma} = k_1$ and $yx = k_2$ should intersect only ...
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Understanding the definition of enthalpy [duplicate]
My chemistry text describes Internal Energy (U) of a substance as the sum of all categories of energy, i.e., Kinetic (temperature), potential, bonding, etc.
Then, Enthalpy is defined as:
$$H=U+PV$$
...
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Enthalpy in an irreversible isobaric process
I know that in a reversible isobaric process, the enthalpy change of the system is the change in heat for that system. What happens if the process is not reversible? I.e only the outside pressure is ...
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Boiling of liquids and their vapour pressure [closed]
Hello I was wondering about the boiling of liquids, I will use water as an example.
Liquids boil when their vapor pressure function p(T) exceeds the ambient pressure, for example water boils at 100 °C ...
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∆G or ∆G° to predict spontaneity
I have a doubt about using Gibbs free energy to predict the spontaneity of a reaction.
It is shown that ∆G = ∆G° + RT ln (Q).
That said, in order to predict which direction the reaction spontaneously ...
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Is it necessary criteria that we draw Ellingham diagram for only one mole of oxygen consumed for a given reaction
In my textbook and many other reference text shows Ellingham diagram for only one mole oxygen consumed. Why is this done?
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How can I find vapour properties of a compound molten salt?
I'm carrying out thermal-hydraulic simulations of the Aircraft Reactor Experiment (a nuclear molten salt reactor) based on circulating molten fuel salt: NaF 53 mol%, ZrF4 41 mol%, UF4 6 mol%.
While ...
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Calculating internal energy change of a reaction
We are asked to find the relation between $\Delta H$ and $\Delta U$, and also, the sign of the internal energy change of reaction:
$$\ce{CO(g) +\dfrac{1}{2}O2(g) -> CO2(g)}$$
This was part (3) ...
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Why is ΔE described as Q-W and Q+W in different contexts?
Depending on the textbooks looked at, the energy change is described as either Q+W or the signage is changed to Q-W. Which is correct? Is it solely context dependent? Could anyone explain the ...
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Explaining Vapour Pressure and Evaporation by Chemical Potential
According to the coexistence curves, both gas and liquid phases can only exist when the chemical potential of both phases are equal.
Does this mean above and below the coexistence curve of liquid and ...
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Chemical potential and condition for equilibrium in case of binary liquid reaction mixture
Suppose there is a liquid mixture with components A and B in equilibrium along with their vapours. Then with the Gibbs-Duhem equation we know that $$μ_A(\mathrm{liquid}) = μ_A(\mathrm{vapor})$$ and
$$...
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Are phase transitions reversible when performed at supercooled temperatures?
For the state transition of supercooled water to ice, is the process reversible? I wonder this because I want to know if I can use entropy change of the universe is 0. If it isn't reversible, how do ...
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Why does the plot of volume and temperature have a kink in a second order phase transition?
The $(b)$ part of the figure shows how thermodynamic variables change in a second order phase transformation.
We observe there is a kink in the plot of volume with temperature.
Why is that so?
The ...
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Is q=0 for irreversible adiabatic process?
Well, I am a little bit confused about this question. I learn that reversible adiabatic processes are isentropic. So $\Delta S=0$. Through $\Delta S=\frac{ q}T$, we can say that $q=0$. But if you take ...
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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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Is electrode reduction potential dependent on the nature of the solution(the reagents of the solution) it's dipped in?
I'm undergrad student majoring in materials science and engineering. I faced this question while studying for a course named "surface engineering of materials".
This slide is a part of my ...
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Work Done by the gas in Isothermal Condition against constant external pressure
Question :
*
Under isothermal condition, a gas at 300 K expands from 0.1 L to 0.25L
against a constant external pressure of 2 bar . The work done by the
gas is( given that 1L.bar=100J)
Answer (from ...
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The entropy change during micellization
I was reviewing the thermodynamics of micelle formation from the Wikipedia page and this book. I understood most of the arguments but micellization is supposed to be an entropy driven process with a ...
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Concept of Absolute Thermodynamic Activity
In the textbook Electrochemical Systems by Newman and Alyea, Chapter 14: The definition of some thermodynamic functions, chemical potential of component (ionic or neutral) is written as a function of ...
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Calculating melting temperature of water with thermodynamical data
So at zero degrees celsius($\pu{273 K}$), for clean water, we have the equilibrium eq.:
$\ce{H2O(s) = H2O(l)}$
As it is at equilibrium, we know that $\Delta G = 0$. As we are dealing with clean ...
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How do I find entropy change for surroundings?
I know how to calculate entropy change of the system but am not able to calculate entropy change for surroundings. The question is as follows:
Q: At $100°C$, water vapour at $1$ bar is in equilibrium ...
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What causes the "Gd break" in the trend of lanthanide-EDTA formation constants?
Smith and Martell obtained a series of data for the binding of trivalent lanthanide ions, $\ce{Ln^3+}$, with various carboxylic acid ligands (amongst them the well-known EDTA).1 A graph of the ...
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What is the degree of freedom of the calcium carbonate dissociation reaction?
Question
$\ce{CaCO3}$ dissociated in a closed system according to the reaction:
$$\ce{CaCO3(s) -> CaO(s) + CO2(g)}$$
Assuming the reaction is in thermodynamic equilibrium, what is/are the degree(s)...
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Virial theorem confusion
Virial theorem says that $E_{t} = -\frac{E_{P}}{2}$ however this says that lets say for 2 gas molecules(Ne) the kinetic energy due to temperature a molecule of $Ne$ at 0K will have the same energy ...
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Are all exothermic reactions spontaneous?
$\ce{GaAs (s)}$ is used in solar cells deployed on satellites found in the orbit of Earth. The best way to make these materials is through a technique called "molecular beam epitaxy", in ...
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How can we define a non-spontaneous reaction?
Consider a reaction:$$\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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If I know the freezing point of two solutions, and combine them into one solution, what is the resulting freezing point?
I am not knowledgeable in chemistry in any way, so I'm sorry if I seem stupid or something.
Suppose I have two solutions which I know the freezing point of, and I combine them into one solution. How ...
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Why does an exothermic/endothermic reaction have a negative/positive enthalpy
So regarding change in enthalpy and exothermic/endothermic reactions, I think I have some conceptual understanding but I'm missing some things.
My current understanding is that:
Given a reaction, if ...
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How to find the current transferred to the anode and cathode of a lithium ion battery at different voltages?
I am trying to find the current transferred to the anode and cathode of a lithium ion battery at different voltages. I know the temperature (approximately) of the battery, the battery's starting ...
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Watercolor pigment conundrum - can a change in ionic profile induce flocculation?
A client of mine has installed an ion exchange water purifier to de-harden her tap water. After that, however, she noticed that it has negatively affected her watercolor painting. From what she ...
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How to calculate the heat released when sodium hydroxide is dissolved in hydrochloric acid solution?
How to calculate the heat released when sodium hydroxide is dissolved in hydrochloric acid solution? Here is the data I gathered from a lab experiment:
$50\ \mathrm{mL}$ of hydrochloric acid solution
...
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Why change of gibbs energy per mole is zero at equilibrium?
I was reviewing this concept and thought of this: $\frac{dG}{dt} = \frac{\partial G}{\partial \xi}\frac{d \xi}{d t}$, for a reaction to be at equilibrium $\frac{d G}{d t}$ must be zero but I have ...
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How can decreasing in temperature indicate an endothermic reaction?
I’m really wondering how can decreasing the temperature refer to an endothermic reaction.
I faced this when I was calculating the heat of a reaction Q in a constant-pressure calorimeter.
What I ...
