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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Why is the Gibbs free energy of titanium(IV) chloride reduction to titanium metal positive?

I use the Ellingham diagram to find the Gibbs free energy at the equilibrium state to find the partial pressure of chlorine. I have to use the Van 't Hoff reaction isotherm and the partial pressure of ...
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Solubility and solubility product in relation to the number of ions in a formula

I was taught that if a salt was formed by ions with higher charges, the lattice energy would be also higher (Born-Landé), and the solubility in water would be lower, as it takes more energy to break ...
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Are Cp and Cv functions of temperature?

I have read that Cp and Cv are independent of temperature for the case of a perfect gas whereas for an ideal gas it will vary with temperature. The variation in Cp and Cv with temperature is ...
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Determine the sea level specific weights of liquids in lbf/ft 3 having densities of : a. 1.75 slug/ft 3 b. 62.6 lbm/ft 3 with g = 32.2 ft/ sec 2 [closed]

Determine the sea level specific weights of liquids in pound force/ft^3 having densities of : a. 1.75 slug/ft^3 b. 62.6 pound mass/ft^3 with g = 32.2 ft/ sec^2
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Standard Enthalpy of Formation

I have hard time understanding why in the definition of standard enthalpy of formation (SEF), the reactants and the products are required to have fixed temperature and pressure. Specifically, ...
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Does the acidity constant depend on the solvent?

Today I came across $pK_a$ values that depend on the solvent. For the hypothetical reaction $HA \rightarrow H^+ + A^-$, I had in mind that the acidity constant is defined simply as $K_a = \frac{\{H^+\}...
3 votes
2 answers
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Total entropy change for reversible reactions and its relationship to equilibrium constant

I'm in year 12 of school doing A2 chemistry learning about entropy and its relationship to reversible equilibria. I learned about the following three ideas from my course book (verbatim), for a ...
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The effect of temperature rise on the kinetics of a non-equilibrium exothermic reaction

I know that based on the Arrhenius equation, reactions kinetic rise in response to a higher temperature. I would be grateful if somebody could explain to me the effect of temperature rise on the ...
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How do I calculate enthalpy change calculations questions?

Below is a question I'm struggling with. When $\pu{0.1 mol}$ of aqueous potassium hydroxide was added to $\pu{0.1 mol}$ of nitric acid, $\pu{5200 J}$ were transferred to the surroundings. What is the ...
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Use the first law of thermodynamics to derive the pressure as a function of T, U, V and N

I am struggling with a thermodynamics question given $$S(U,V,N)=C_VNK_\mathrm b\ln U/U_0+NK_\mathrm b\ln V/V_0$$ (where $U_0$ and $V_0$ are the reference energies and volumes) and the first law of ...
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Can chemical potential be directly measured like this?

I have a system of a pure ideal gas $a$, which I call 'the reference', with a known $P^{ref}, V^{ref}, T^{ref}$ and $n^{ref}_a$. I know the chemical potential formula for an ideal gas, so can ...
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What’s the physical meaning of (∂v/∂T )P?

I'm solving this exersice: The equation of state of a Van der Waals gas is \begin{equation} \left(P + \frac{a}{v^2}\right)(v-b) = RT \tag{1} \end{equation} Where $a$,$b$ and $R$ are constants. ...
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Is there a see through material that can endure 2000°C?

I was wondering if there is a transparent material that can endure temperatures up to 2000°C but doesn't deform at these high temperatures. This material doesn't have to be glass, it can be plastic or ...
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1 answer
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Adiabatic Venting of Propane Tank

A few weeks ago, a question was submitted regarding adiabatic venting of a chlorine cylinder: Issues with Chlorine Liquefaction The member submitting the question was interested in why the stream ...
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1 answer
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Is there a general equation which calculates the temperature which shifts the equilibrium mostly to the right which applies to most reactions? [closed]

Say I have the following simple reaction $ \ce{HCl(aq) + NaOH(aq) \rightarrow NaCl(aq) + H2O(l)} $ Does there exist a calculation which gives the ideal temperature for this reaction to occur at? ...
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Calculating the enthalpy of sweat evaporation

The following is a textbook question and answer: Evaporation of sweat requires energy and thus take excess heat away from the body. Some of the water that you drink may eventually be converted into ...
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2 answers
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Issues with Chlorine Liquefaction

A common problem that occurs when releasing chlorine from cylinders during industrial chlorination processes is that of liquefaction of the gas and ice deposition in and around the cylinders which ...
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Help understanding Isothermal titration calorimetry ITC

Trying to understand Isothermal titration calorimetry: ITC , from a public online forum (Off-topic question related to ITC binding studies) I got this question: We performed an ITC binding study (...
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1 answer
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Gibbs Free Energy of Ideal Gas in Carnot Cycle

Let's just say we have 2 moles of monoatomic (maybe helium) ideal gas that is doing a Carnot Cycle with reservoir temperature of 300 and 750 K. Now, here's a simple question, what is the Gibb Free ...
7 votes
2 answers
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Why do we call salts such as AgCl sparingly soluble?

Though we use the term practically insoluble for salts like $\ce{AgCl}$ in inorganic chemistry, we preferably call them "sparingly" soluble salts in physical chemistry seeing their tiny ...
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2 answers
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Comparing the enthalpy change between the formation of water in two states

The enthalpy of the reaction $\ce{H2(g) + 1/2 O2 (g) -> H2O (g)}$ is $\Delta H_1$ and that of $\ce{H2(g) + 1/2 O2 (g) -> H2O (l)}$ is $\Delta H_2$. Then, a) $\Delta H_1 < \Delta H_2$ b) $\...
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3 answers
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How is the entropy of mixing related to chemical reactions in solution?

When calculating the Gibbs energy of reaction for reaction mixtures at arbitrary concentrations, you use the following expression: $$\Delta_\mathrm r G = \Delta_\mathrm r G^\circ + RT\ln Q$$ The term $...
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On Van Der Waals relation: how to derive du/dv = a/v^2 without using the relation dU=TdS−PdV?

I have read several threads and papers which show how to derive $\left(\frac{\partial u}{\partial v}\right)_T = \frac{a}{v^2}$ by using the Maxwell's relation $\left(\frac{\partial{S}}{\partial{V}}\...
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How to compute backward reaction rate from forward one and an equilibrium data

Suppose we have have an ideal gas mixture and a reversible elementary reaction: $$ \ce{O + H_2 <=> H + OH} $$ Its forward reaction rate may be computed as follows: $$ \frac{d[\ce{H}]}{dt} = \...
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What makes a compound high or low energy and why does that relate to reactivity? [closed]

After reading about thermodynamic stability, it now makes sense to me how the enthalpy of a reaction relates to the thermodynamic stability of a compound. However, when looking for a clear way to ...
2 votes
1 answer
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Does the nature of the H-A bond tell us about the $\Delta$G of an acid's dissociation?

When I first learned about acid strength trends in general chemistry, I remember it was explained in terms of the character of the H-A bond. The more polar the H-A bond, the easier it was to ...
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Calculating pourbaix diagram of Fe-H2O system at different temperatures

I have been trying to calculate the pourbaix diagram for Fe-H2O at different temperature for my high school research but I am facing a lot of problems. I have several question regarding the ...
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2 answers
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Spontaneity criterion for phase transformations and chemical reactions [closed]

Why is the Gibbs free energy (G) considered a spontaneity criterion for phase transformations and chemical reactions? Why are other thermodynamic parameters such as enthalpy (H), entropy (S), and ...
2 votes
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Chemical potential vs derivative of free energy

Let $x$ be the concentrations of species in a chemical system, and let $G(x)$ be the Gibbs free energy. My understanding is that the chemical potentials should be given by $$ \mu_k = \frac{\partial G}{...
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How to calculate corrected Gas Volume?

We are working on a project called 'Electronic Gas Volume Corrector'. The device reads pressure and temperature from sensors mounted on a gas pipe and gas volume from a gas meter. These are the ...
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Alternate formulation of h(P,T)?

I'm using the following handbook "Engineering and Chemical Thermodynamics 2nd edition" by Koretsky. In the book they have an alternate formulation for h(P,T) though it was never explained ...
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Why is rapid expansion/compression reversible?

I am looking over the Otto Cycle on this MIT website and it says at one point "the processes from 1 to 2 and from 3 to 4 are isentropic" in reference to the expansion and compression of the ...
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Calculation of the Seperation factor of Ethanol / Water rectification based on two saturated vapor temperatures

I want to calculate the efficacy of a Water / Ethanol rectification based on two temperatures with help of a vapor-liquid equilibration diagram. The first temperature is measured right above the ...
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Why does equilibrium of ice and water only exist at 273K at normal pressure?

I am a high school student and I am a little confused in the concept of spontaneity of a reaction and how equilibrium works for a reaction, I got some confusions: Let's take example of freezing of ...
1 vote
1 answer
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Question on Thermodynamics from a recently conducted Examination

This is a question from the recently conducted JEE Main exam (in India). I had solved it myself, but found the answer to be incorrect. Here's the question. Here is how I solved it: $\Delta H = \pu{41....
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What is the necessary and sufficient condition for a mixture to be ideal?

I am trying to understand some concepts from solution thermodynamics related to ideal mixtures and fugacity. My main question is what is the necessary and sufficient condition for a mixture to be an ...
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1 answer
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Isolation is a Consequence of Definition [closed]

Let's consider a ballon, such that it has an adiabatic wall, and there is no exchange of heat with the surroundings. Now, let the balloon wall be completely impermeable to the movement of matter ...
1 vote
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Should change in enthalpy be zero in galvanic cells?

When an exothermic redox reaction happens by just mixing the reagents, the change in enthalpy at constant pressure equals heat which is consistent with the fact that: For a closed system at constant ...
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What non-toxic non-corrosive liquids are used for heat transfer?

I have a steel vessel placed concentrically within a larger steel vessel, resulting in air-filled annulus (air gap) between the two vessel walls (figure below). Due to the existing vessel construction,...
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How do you calculate the internal energy of a mixture of real gases?

Is there an equation to calculate the internal energy of a gas mixture, or is it too complicated to be computed so simply? I know that there's $E_{internal}=N(degrees of freedom)\frac12kT$ and $(P+a\...
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Calculating the amount of water condensed when cooling below the dew point

I've been given the following question: Calculate the dew point temperature of a 60% humid air at $30^oC$. How much water mass wil condensate out of 1 $m^3$ of such air when the temperature is ...
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Evaporation of zinc oxide

My question involves the evaporation of silicate material (e.g., rocks, minerals, geologic material), specifically I am trying to work the number of electrons (n) that are involved in the evaporation ...
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How do I calculate the temperature change in a gaseous reaction?

So, with $\pu{3 mol}$ of $\ce{H2}$ and $\pu{3 mol}$ of $\ce{Cl2}$ and given the reaction $\ce{H2(g) + Cl2(g) -> 2 HCl(g)}$ with $\Delta H=\pu{-184.6 kJ/mol}$, I am supposed to calculate the work ...
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How is reaction enthalpy equal to heat in a coffee cup calorimeter?

In explaining how to evaluate data from a coffee cup calorimeter, textbooks often claim that $$ \Delta H = q $$ This makes sense for an isothermic calorimetry experiment, where the temperature of the ...
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Effect of degree of freedom on entropy change during a reaction

In the reaction $$\ce{C_{(s)} + O2_{(g)} -> CO2_{(g)}} $$ one mole gaseous reactant gives one mole gaseous product, so there is no significant change in entropy. It can be verified by line of $\ce{...
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Why is it necessary for the standard enthalpy of fusion to change at the transition temperature?

I have a table here: For argon, for example, shouldn't the standard enthalpy of fusion @ 83.81K be 0 J/mol? After all, it is already at the respective transition temperature.
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In regards to the Gibbs free energy equation, it seems that the two terms oppose one another, Enthalpy and -TS. Can you explain this?

So for example, if H is endothermic, then the enthalpy term is positive, meaning energy is absorbed by system overall, meaning net bonds broken, meaning the equation leans towards nonspontaneity. If ...
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Does mayer's equation change for two mole of ideal gases or is it remains same for any number of moles [duplicate]

Mayer's Formula is given by: Cp – Cv = R But is the relation remains same for two mole of ideal gas, or is it Cp - Cv = 2R As, far as i know the number of moles are cancelled out in the derivation. ∆H ...
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Thermodynamics derivatives: Does $(\partial A/\partial B) = (\partial B/\partial A)^{-1}$?

If I need to find, for instance: $$\mathcal{T} := \left(\frac{\partial U}{\partial S}\right)_{V, N}$$ knowing: $$\left(\frac{\partial S}{\partial U}\right)_{V, N} = \frac{1}{T}$$ Can I say that $\...
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What endothermic reactions can be effectively reversed by electrolysis?

Not only newbie, but total layman here; please be patient with me. Given are either two different elements, two different molecules, or one element and one molecule (chemical A and chemical B). A and ...

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