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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Do all thermodynamic processes have a final state?

I am certainly not a chemist, and equations scare me. But I was wondering, can there can be a thermodynamic process that has no final state (perhaps a reversible process)? Can such a process ever ...
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How do I calculate the average initialisation time of a reaction? [closed]

I want to know the mean average after which, for example, H2 and O2 react under standard conditions. As there is enough energy in the system to start the reaction, it should just be a matter of time ...
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What is the minimum energy required to dessicate an ethanol+water azeotropic solution

I am wondering, how can we compute the minimum theoretical energy required to separate ethanol from a cold azeotropic water-ethanol mixture? Are there industrial processes that are close to the ...
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How it was decided that the freezing point of water in the Kelvin scale of temperature should be 273.15 K? [closed]

While discussing about the different temperature scales, our teacher told us about the freezing point and boiling point of water in different scales. I asked my teacher that how these numbers were ...
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How can I measure the energy contained within water vapor?

Let’s say I have a kilogram of water vapor at $\pu{423 K}$. Can I directly measure the energy, contained as heat, within the vapor? All the laws I know depend on knowing the changes that happened that ...
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2 answers
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When we boil water, does the generated steam remain at the same temperature of boiling point until all water is boiled? [closed]

Suppose we are boiling water in such conditions so that the boiling point of water be $\pu{100 ^\circ C}$. Does the generated steam have the same temperature of 100 C until all water is boiled? And ...
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Calculate relative humidity inside appartment when AS is cooling the air [closed]

I heve this question (from previous semester's test) and I'm not sure if my answer is correct. Consider an apartment of 80 m? with a ceiling height of 2.7 m. Initially, the 50% humid air in the ...
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Interpretation of Helmholtz energy and Gibbs energy

I know that this question has many other variations on this site, but I'm trying to see if I understood Helmholtz and Gibbs energy properly or not. The material I'm reading from is Physical chemistry ...
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Why did industry develop mainly to fix nitrogen in ammonia (Haber-Bosch) instead of in nitrate?

Since approximately WWI, humanity has been able to fix nitrogen gas from the atmosphere ($\ce{N2}$) into compounds that are much more bio-available, like ammonia and nitrate. The first (hard) step is ...
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Why do hydrogen bonds between atoms of the polypeptide backbone, form both helix and pleated structures, instead of only one structural type?

Proteins have segments of their polypeptide chain/chains that can be repeatedly coiled or folded into helix and pleated structures, respectively. This is due to hydrogen bonds between partially ...
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How to compute free energy for solvation using gaussian09? [migrated]

I'm trying to compute the free energy of solvation of a molecule in gaussian09 using the continuum solvation model, but I am haveing difficulties, I don't know how to do it and gaussian manual does ...
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Is the proportion of molecules with sufficient energy to react *really* equal to $e^{-E_A/RT}$?

In A-level chemistry class today I was just told the following: For a reaction with activation energy $E_A$, the proportion of reactant molecules with kinetic energy $\ge E_A$ is: $$e^{-E_A/RT}$$...
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How are the formulae of isochoric processes used in adiabatic processes?

We have the formula for an isochoric process: $c_V = \frac{\mathrm{d}E}{\mathrm{d}T}$ at constant volume. $c_V=$ molar heat capacity at constant volume. But it's given for adiabatic changes, $$\delta ...
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What is the entropy change in isochoric process

I have studied that entropy increases with increase in temperature and it decreases with increase in pressure but in case of isochoric process both are happening at the same time but still the overall ...
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How exactly is heat supplied in an isothermal process

How exactly is heat supplied in an reversible isothermal process. If the temperature of system and surroundings always remains the same, then how come surrounding is supplying heat? I studied that T ...
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Is there an (thermodynamic) equation of state that can be used for solids, liquids, and gases?

Ideal Gas Law and its extension (i.e. van der Waals equation) only works for gases. Navier-Stokes Equation (not an EOS) works on both gases and liquids, but not solids Is there any equation that ...
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1 answer
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What processes generate entropy as heat flows across temperature gradient

Suppose, we have a source at high temperature $T_\mathrm h$ and sink at temperature lower temperature $T_\mathrm l$. If $Q_\mathrm h$ amount of heat flow from source to sink, then change in entropy of ...
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Question about entropy generated in isothermal expansion of an ideal gas

So, this has been bugging me for a while. Consider the isothermal expansion of an ideal gas in a container. As the gas is allowed to expand, it does work on the surroundings which causes the ...
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Thermal properties of chemical compounds [closed]

I have a chemistry related question, I'm doing a research on some inorganic salts (KOH, KCl) and similar compounds and I'm struggling finding the thermal properties like (thermal conductivity, ...
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Is delta S of universe always 0 when an ideal gas undergoes an isothermal irreversible process?

Since for an irreversible process, $$dS_\mathrm{Surrounding} =-\frac{\text{dq}_\mathrm{irr,sys} }{T_{\text {surr }}}\tag{1}$$ where $\text{dq}_\mathrm{irr,sys}$ is heat exchange of system and $-dq_\...
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Do "pseudo Van der Waals" gases exist?

In college, when deriving the Langmuir isotherm for gas-solid adsorption, the professor proposed a modified version of the Van der Waals state equation, what he called the "pseudo Van der Waals ...
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Chemistry Thermodynamics and Sign Convention [closed]

Can anyone pls explain me the sign conventions that we use in chemistry thermodynamics for heat and work...also kindly explain how to identify what will happen to heat in positive or negative work and ...
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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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If change in enthalpy is defined for a reaction going to completion, how is it measured for reactions that don't? [closed]

I read that $\Delta H$ is the energy absorbed or released for a reaction going 100% to completion(here). However, what we would be measuring in a calorimeter would be the reaction going from initial ...
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In gas law equations, if volume and temperature are directly proportional, why can't we write the equation as temperature divided by volume? [closed]

In gas law equations, volume, temperature, pressure and amount of substance may vary. In the simpler equations, like Charles' and Amonton's, temperature and pressure/volume are directly proportional. ...
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Does the equilibrium constant of an ideal liquid mixture reaction depend on pressure?

I want to calculate the equilibrium constant K[T] for a the following reaction: $$\ce{CH3OH(l) + C4H8(l) -> C5H12O(l)}$$ It is assumed that the mixture is ideal and the reaction takes place at 14 ...
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How to calculate the buffer capacity for polyprotic acids? specifically H2PO4 --- HPO42- + H30+

as the title says. Is b= amount of OH-/ H3O divided by volume of buffer x change in pH wrong to use with polyprotic acids? Can I calculate the buffering capacity of a sodium phosphate buffer made up ...
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If liquids absorb heat from their surroundings to become gas, why does gas feel hotter than liquid?

I know what you're thinking, "OP, are you for real!? Gas is obviously hotter because it absorbed heat from the environment!" But hear me out. Yes it is hotter in absolute terms because it ...
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Are solid fuels with calorific values >= 10,000 kcal/kg (42 MJ/kg) physically possible?

I have seen laboratory documentation from a reputable lab in southeast Asia that a company has achieved a solid fuel product made from landfill material with a high heating calorific value ($CV$) of ...
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Kirchhoff's law (Thermodynamics) [closed]

For the following question: The standard enthalpy of formation of the metallocene bis(benzene)chromium was measured in a calorimeter. It was found for the reaction $\ce{Cr(C6H6)2(s) → Cr(s) + 2C6H6(g)...
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Why does copper(II) sulfate react with potassium iodide in aqueous solution?

According to the list of standard reduction potentials [1, p. 5-79] $E^\circ(\ce{Cu^2+/Cu^+}) = \pu{+0.153 V},$ while $E^\circ(\ce{I2/I^-}) = \pu{+0.5355 V}.$ Doesn't it mean that iodine has more ...
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How are fundamental equations valid for both reversible and irreversible processes?

We know for an irreversible process, $\mathrm dS\gt\mathrm dq/T$. And if the process is done at constant pressure we can take the equation as $\mathrm dH-T\,\mathrm dS\lt0$. And we defined Gibbs ...
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what's the difference between gas and vapour? [duplicate]

In the lecture, our teacher said that the significant difference between gas and vapour is we can't liquefy gas just by compressing it but it's not the same in the case of vapour." So, I'm ...
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How come nuclear waste is so radioactive when uranium is relatively stable with an extremely long half life?

Natural uranium has a half life of 4.5 billion years. Representing with the expression $m(0.5)^{\frac{x}{(4.5\times10^9 \times 364)}}$, where $x$ is in days and $m$ is the initial mass of uranium. In ...
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How can the heat equation be used to model temperature vs time in a solubility experiment?

Background: I am doing experiments trying to map the practical solubility of a certain chemical species called an "activator" solution. This solution is essentially a sequential mixture of ...
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How to determine whether a reaction is possible by using a phase diagram?

Given the following phase diagram for a binary mixture of $\ce{MoO3}$ and $\ce{Bi2O3}$: I am asked to determine whether from $\ce{Bi2O3}$ and $\ce{Bi6Mo2O15}$, can $\ce{Bi10Mo3O24}$ and $\ce{...
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How to calculate thermodynamic parameters from quadratic form of the Van't Hoff Equation?

I have drug binding data giving me Ka values for a set of associated temperatures. This allows me to plot ln(Ka) vs. 1/T, which I can fit to a second degree polynomial i.e. y = ax^2 + bx + c. From ...
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How does Hess' Law work exactly? [closed]

So I am talking about complicated compounds and not simple reactions where you subtract heats of formation. I was trying to find the heat of reaction for an aryl substituted methyl aryl sulfide being ...
2 votes
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Diffusion vs mobility and the Einstein relation

This former question is about the mobility constant $M>0$ in the Cahn-Hilliard equation. To determine the value of such a mobility for a simulation study, Kim and Sanders (2020) use the formula $$ ...
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Why does NaCl form when it requires 1.52 eV of energy? [closed]

An atom of sodium has one 3s electron outside a closed shell, and it takes 5.14 eV of energy to remove that electron. The chlorine lacks one electron to fill a shell, and releases 3.62 eV when it ...
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1 answer
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How do you achieve the exchange of reactants even though it is energetically less favourable?

Assuming that in a system the following pairs are energetically most favourable: AB and CD. I now heat the system until all bonds are broken. How do I achieve the following reaction: A+B+C+D -> AC +...
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4 votes
0 answers
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How to estimate the mobility constant and the surface energy parameter in the Cahn-Hilliard equation?

As a mathematician, I want to simulate phase separations with the Cahn-Hilliard equation $$ \frac{\partial c}{\partial t} = M \Delta \bigg(\frac{\partial \mu}{\partial c} - \kappa \Delta c \bigg), $$ ...
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Which energy increases when compression work is done on a gas?

When a gas is compressed using external pressure (piston-cylinder assembly) we say work is done on the gas and it increases the internal energy of the gas. Where does this work mainly go ? Does it ...
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Why is the relationship between molar mass and boiling point for alkanes a square root relationship?

I plotted the boiling point of alkanes against their molar mass and found the following trend: I expected the trend would be linear, since (based on my understanding of what I've learned in class so ...
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Is the formation of starch from glucose in plants an endothermic or exothermic reaction?

If I understand it correctly photosynthesis is an endothermic reaction. Energy from the sun is used to form glucose. Next the glucose is turned into starch. Would this be a combination reaction? If so,...
1 vote
2 answers
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Confused why delta ∆Q and dQ don't make sense for heat Q

In my chemistry teacher's notes, some notations concerning the heat $Q$ are marked as inappropriate. $Q$: yes d$Q$: no $\delta Q$: yes $\Delta Q$: no In the second bullet in the screenshot below, ...
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Standard state clarification

I have seen several questions on standard states, but none quite get at the issue I'm having in understanding them. In Elements of Physical Chemistry by Atkins and de Paula, they describe standard ...
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1 answer
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Formation of AZ91 Magnesium Alloy

I have been researching on how to form AZ91 Common Magnesium Alloy which consists of 90% Mg, 9% Al, 1% Zn, 0.3% Mn. Referring to the article at here, I have read and highlighted important text and ...
3 votes
1 answer
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How can combusted methane from landfill samples be quantified?

Background: For my studies I'm wanting and attempting to make a landfill greenhouse gas emissions (GHG) model that predicts the amount of greenhouse gas equivalent emissions ($GHG_\mathrm{eq}$ [tonnes/...
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Why can we add/substract/cross out chemical equations for Hess law?

Suppose I take the model example: (1) $\ce{C + 1/2 O2 -> CO}$ (2) $\ce{CO + 1/2 O2 -> CO2}$ Adding both together: (3) $\ce{C + CO + 1/2 O2 + 1/2 O2 -> CO + CO2}$ (=> $\ce{C + 1/2 O2 + 1/2 ...
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