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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Are there heat transfer fabrics?

I’m curious to know if there any fabrics or gels that would be able to cool down when heated. In particular one that could be shaped into a horse sheet, or filled with some substances to do the same ...
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Does pressure affect the enthalpy of formation?

In a complete combustion reaction, coal and air (both at $300K$ and $2$ atm) react to produce carbon dioxide which exits the reactor at the same temperature and pressure as it entered. $$\mathbf{C+O_2}...
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Dependence of Chemical Potential in Derivation of Clapeyron Equation

The "standard" derivation of the Clapeyron equation begins with considering two phases $\alpha$ and $\beta$ that are in equilibrium. The claim made is that $$\mu^\alpha(T,P) = \mu^\beta(T,P)$...
Neel's user avatar
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Why does variation of heat capacity as a function of temperature support the theory of particle nature of light?

In my chemistry textbook, it states that the theory of EMR in the 19th century could not explain certain phenomena like black-body radiation, the photoelectric effect, etc. Another phenomenon listed ...
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Why is the entropy change of surroundings in free expansion zero?

I have read that what differentiates an irreversible process like adiabatic free expansion from its counterpart reversible process — isothermal expansion, which takes the system to the same final ...
Jeff Jefferson 's user avatar
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Doubt regarding free and adiabatic expansion

I recently came across the topic of irreversible expansion in thermodynamics. Suppose we have a container of gas with a piston (not mentioned whether massive or not), and we allow a free and adiabatic ...
Lucifer's user avatar
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why is 1 calorie 4.186 joules? [closed]

What is the experiment that shows 1 calorie is equivalent to 4.186 joules called? I found one mention of an experiment that attached a weight to a prop and the friction of the water causes the ...
Cameron Austin's user avatar
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Information about Rankine scale [closed]

What is the use of the Rankine scale? Why cannot we use international units? Why is there need of such a unit? If we want we can also make new units. Why is not US using international system? It it ...
Himanshu kaushik's user avatar
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Why is the boiling point of alcohols primary > secondary > tertiary? [duplicate]

If I have 1-butanol, 2-butanol, and 2-methyl-2-propanol, the boiling points of each are 117, 99, and 82 degrees Celsius, respectively. Why does that happen knowing that all of them have the same ...
omar waled's user avatar
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Calculation of Reaction Extent as a Function of Pressure and Temperature: Issue with Activity-Based Approach

I'm working on modeling reactions involving combinations of hydrogen (H), nitrogen (N), and strontium (Sr) elements. I've obtained the temperature-dependent Gibbs free energy of formation, enthalpy, ...
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Confused about free energy equation and entropy change

I'm confused about two equations and how they relate to each other. These are $\Delta S = \Delta Q/T$ and $\Delta G = \Delta H - T\Delta S$. To derive the Gibbs' free energy change for the universe ...
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Could an airborne swarm of small insects explode? [closed]

I know that fine-grained organic matter such as flour or pollen can be quite explosive if ignited. It also seems logical to me that the explosiveness of such an organic powder is determined by many ...
paulina's user avatar
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How does cell potential change with temperature for positive enthalpy and negative entropy?

A recent United States National Chemistry Olympiad question asked: A certain voltaic cell has a standard cell potential that increases with increasing temperature. Which best explains this ...
unstable's user avatar
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With two reagents common on Mars, fluorite and CO2, how would I produce carbon tetrafluoride?

The hypothetical terraforming of Mars would require the heating of the atmosphere. A commonly suggested method is the in-situ production of fluorocarbons, powerful greenhouse gases. For example, ...
Galerita's user avatar
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Concentrating acetic acid from vinegar? [closed]

I'm currently planning to freeze out the acid and then filter it through a chilled filter set up. My end goal is to use this in combination with sodium bicarbonate to deliver a large amount of thrust. ...
Dex Cool's user avatar
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What is change in gibbs free energy of a reaction actually telling us? [closed]

$\Delta G=\Delta G^o+RT\ln Q?$ In this equation, what does $\Delta G$ mean? Is $\Delta G$ the change in gibbs free energy if we complete the reaction (convert all products to reactants)? That doesn't ...
ThatApollo777's user avatar
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How can a "reversible" reaction occur both ways?

Take a general reaction $\ce{A -> B}$ with $\Delta G<0$, it must be the case that $\ce{B -> A}$ has $\Delta G > 0$ (or vice versa.) Now, if the reaction is "reversible", i.e. $\...
TheAnonymous's user avatar
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1 answer
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Heating a Single Water Molecule [closed]

From my understanding, phase changes break/form bonds between molecules of the same substance. Assuming this is in a vessel at 1atm of inert gas, if I have one molecule of water with no bonds to other ...
Camel Camel's user avatar
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What is the energy of sum of ionic equations?

Say energy depends on the relative number of ions in the mixture, and factors P, and T. $$ u = u (P,T,x_1,x_2,...,x_{n-1}) $$ Mixing two solutions at the same temperature, may change the temperature ...
ananta's user avatar
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When to use Heat of Products - Heat of reactants and Heat of reactants - Heat of products when calculating enthalpy change

In my schoolbook there are multiple questions where I have to calculate the enthalpy of formation, heat of reaction, enthalpy of reaction, etc etc. But sometimes the formula to be used is Hp - Hr, and ...
pag's user avatar
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Absolute entropy of a compound at a given temperature is S0→T=∫Cp(T)Tdt + ΔH(trans)/T(trans).Is there an assumption of constant pressure here?

Change in entropy of system is given by dQrev/T, Qrev=nCpdT for ideal gas only at constant pressure,so when we find absolute entropy of a gas by integrating nCpdT from 0K, is constnat pressure ...
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Variable in Thermodynamics

While studying Physical Chemistry, I came up with this question. As I derive equation C_p-C_v, I found the equation (dQ/dT)p = T(dS/dT)p (d-> round) As I know, dQ=TdS so dQ/dT=(Tds/dT). and I'm ...
junstar's user avatar
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Why does Cs2SO4 have more lattice energy that Na2SO4?

My chemistry teacher told us that $\ce{NaF}$ has a higher lattice energy than $\ce{CsF}$. He explained it by telling lattice energy is inversely proportional to size of ions added. He then mentioned ...
Rajath's user avatar
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Different definitions for work in physics and thermodynamics [duplicate]

In physics, work is defined as the force applied on an object multiplied by the distance traveled by that object. However, in thermodynamics, work is defined as a function of the opposing force. For ...
SerMig1111's user avatar
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Pressure in Clapeyron and clausius Clapeyron equation

The Clapeyron equation is $\frac{\mathrm{d}p}{\mathrm{d}T}=\frac{\Delta S}{\Delta V}$. Here, is the change in pressure 'dp' actually a change in external pressure that is being applied on the whole ...
Natasha J's user avatar
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3 answers
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Interpretation of a Phase Diagram

I am a bit confused about the correct way to interpret a phase diagram. I was told that the line separating the liquid and gas phases gives the vapor pressure of the liquid substance as a function of ...
Johnny Smith's user avatar
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Why does enthalpy change and not internal energy help in determination of spontaneity?

Spontaneity of a process is measured by Gibbs Free Energy $$\Delta G= \Delta H-T\Delta S$$ $$\Delta H=\Delta U+\Delta (PV)$$ Is there an intuitive explanation for why Gibb's energy depends upon ...
Portuguese Man Of War's user avatar
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What is the pressure of triple point and melting point for ethyl chloride?

I need the information for pressure of triple point and melting point for ethyl chloride but on the internet I found only information for temperatures which are 134,5K and 134,82K.
Patricia's user avatar
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If Internal energy can be changed by doing work also, then how come internal energy is zero in a isothermal process involving non zero work?

In the equation of First law of thermodynamics $∆U = q + w$, where $U$ is the internal energy, $q$ is the heat supplied and $w$ is the work done. It is said that for an isothermal process, since the ...
Synthia's user avatar
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3 answers
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How is it even possible that vapour pressure of liquid and vapour of solid are equal at freezing point? [duplicate]

My text book states The freezing point is defined as "the temperature at which the vapor pressure of the substance in its liquid phase is equal to its vapor pressure in the solid phase" Also ...
Aditya's user avatar
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2 answers
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How to use the thermodynamic identity in a reversible process

I have trouble wrapping my head around the thermodynamic identity. From Schroeder's book "An Introduction to Thermal Physics," I understand that entropy is defined as $$\mathrm dS=\frac{δQ}T\...
DracoArtist's user avatar
2 votes
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Calculating the enthalpy of formation for ethane in Gaussian

I am attempting to run a benchmarking calculation in Gaussian software to obtain the enthalpy of formation for a series of molecules. I am using the example calculation found here for ethane (C2H6). ...
Zephyr Solabella's user avatar
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Why is reaction rate proportional to the order of reactants? [duplicate]

I know that for some elementary reaction $m\text{A}+n\text{B}\rightarrow\text{C}$, the rate of reaction is given by $-\frac{\text{dA}}{\text{dt}}=k[\text{A}]^m[\text{B}]^n$. Now if we consider the ...
Chitraksh Pandey's user avatar
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1 answer
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Number of state variables in the general expression for a state function

In the tenth addition of Physical Chemistry: Thermodynamics, Structure, and Change by Peter Atkins and Julio de Paula, it is given, in section 2E, that the general expression for the differential of ...
ananta's user avatar
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Temperature dependence of enthalpy in electrochemistry

I've been trying to use Kirchoff's law to determine the difference in the enthalpies of electrochemical reactions at different temperatures for a general electrochemical process. So here's my progress:...
Cognoscenti's user avatar
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2 answers
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Can phase tranformations occur with change in temperature? [closed]

I know that, usually, phase transition occurs with a fixed temperature. Is there a case where this is not followed? Can phase transformations occur with changing/variable temperature?
ananta's user avatar
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Why doesn't HBr show allylic substitution in presence of Peroxide?

HBr reacts with alkenes such as propene in the presence of Peroxide as per the Anti-Markovnikov rule. This is an addition reaction, forming 1-bromopropane as the major product. This happens due to the ...
Maddy's user avatar
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Simple explanation of the maximum work theorem

I have been trying to understand the maximum-work theorem for some time. But it seems like an impossible task, and it is a very confusing concept. First, the sign convention of work is different in ...
ananta's user avatar
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3 answers
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Definition of Gibbs Free Energy and its interpretation [closed]

RELATIONSHIP BETWEEN $\Delta G$ & $W_\mathrm{non-PV}$ $dU = dq + dw_\mathrm{py} + dw_\mathrm{non-PV}$ for reversible process at constant T & P $dU+pdV-TdS = dw_\mathrm{non-PV}$ $dH-TdS = dw_\...
Sai's user avatar
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1 answer
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How to measure heat transfer and heat dissipation in a kitchen?

I am a chemistry beginner just starting to coming to grips with stoves and Bunsen burners. I would like to know, what kind of instrument can I use to measure the amount of heat transferred from a ...
Joselin Jocklingson's user avatar
1 vote
1 answer
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What is the significance of PV in Enthalpy (H=U+PV)? Are we adding work twice in the equation? [duplicate]

I have 3 questions: Enthalpy is defined as: H = U + PV What exactly does PV signify? Also from the First Law of Thermodynamics ∆U = q + w w here means work (done by, say, the system). So, ∆H = q + w ...
apm's user avatar
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2 votes
1 answer
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Partial derivative of the Gibbs free energy with respect to temperature at constant enthalpy

I am trying to find the expression for $\left(\frac{\partial G}{\partial T}\right)_H$ as a function of the entropy $S$, temperature $T$, $C_p$ and $\alpha=\frac1V\left(\frac{\partial V}{\partial T}\...
Gouge's user avatar
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2 votes
1 answer
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Determine equilibrium stability transition of a reaction (function of temp and concentrations)

I am trying to calculate and plot the stability of $\ce{Fe3O4 - FeS2}$ based on the chemical equation: $$ \ce{Fe3O4(s) + 6SO2(g) + 16CO(g) -> 3FeS2 (s) + 16CO2(g)} \tag{1} $$ I want to plot the ...
learning_physics's user avatar
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1 answer
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Confusion regarding the relation between Gibbs free energy and reaction quotient

According to the Wikipedia page on the Nernst's equation, the change in Gibbs free energy is $$ \Delta G = \Delta G^\circ + kT\ln Q \tag{1} $$ But, according to many other sources and also to my book ...
Jeet's user avatar
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2 answers
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Doubt regarding definition of enthalpy

We define enthalpy change as heat released at constant pressure but it is also defined for process where pressure varies. How do I understand this?
Aarush Saharan's user avatar
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2 answers
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Definition of Joule–Thomson coefficient with respect to heat capacity at constant volume

Joule–Thomson coefficient is defined as $$\mu_\mathrm{JT}=\left(\frac{\partial T}{\partial P}\right)_H. \tag{1}$$ Using the cyclic rule for partial derivatives it can be written as $$\mu_\mathrm{JT}=-\...
Aarush Saharan's user avatar
1 vote
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Work from a spontaneous endothermic reaction?

Some reactions are spontaneous ($\Delta_\mathrm{r}G < 0$) although they are endothermic ($\Delta_\mathrm{r}H > 0$), e.g. the plastic packs that once cracked they get cold. I saw that it is often ...
Olfaction's user avatar
1 vote
1 answer
231 views

Can a carbocation ever be more stable than a neutral molecule?

The question is about finding the most stable molecule or species. Now my thought process was that cyclopropenylidene(1) was a carbene so would be unstable even though it is aromatic. Cyclopenta-1,3-...
mechanist's user avatar
1 vote
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Estimation methods for temperature evolution of a high $\Delta H_{mix}$ dilution ($\ce{KOH}$ in water)

Question up front: Can temperature evolution in solutions be short-hand-estimated by simple state based calculations - with reasonable expectations of precision? (+/- 10° C) I am trying to calculate ...
Stian's user avatar
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van der Waals and the difference Cp - Cv

I would appreciate assistance with the following question please. Show that for a gas obeying van der Waals' EOS, $$\left( p +\frac{a n^2}{V^2}\right)(V-nb) = nRT, $$ and whose internal energy is ...
Mike Welch's user avatar

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