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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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Question regarding enthalpy of sublimation vaporization and fusion

While learning Thermochemistry, I came across the formula $\Delta H_{sub} = \Delta H_{vap} + \Delta H_{fus}$ Now my question is how that when we want to change the phase of a substance from solid to ...
Sarban Bhattacharya's user avatar
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27 views

How to derive absolute temperature scale from Carnot engine?

This question is about how to obtain an absolute or thermodynamic temperature scale using a Carnot engine. The reasoning below appears in the book "Heat and Thermodynamics" by Zemansky and ...
xoux's user avatar
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1 vote
1 answer
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Sign Conventions for Electron Affinity and Electron Gain Enthalpy [duplicate]

In some of the books, negative sign is used for an exothermic Electron Affinity. But in others, a positive sign indicates an exothermic Electron Affinity. Now if we adopt the first sign convention of ...
SameerTahir's user avatar
0 votes
0 answers
26 views

Can Gibbs Free Energy equation be used to explain why some phase changes are exothermic or endothermic?

I was wondering about some ways to explain why some phase changes are exo / endo. I am aware that for endothermic phase changes (boiling, melting, sublimation) energy input is required to raise the ...
hihihuhu74's user avatar
-2 votes
0 answers
59 views

Why do we assume that entropy of H+ ion solution at 298 K is zero? [duplicate]

If we assume that entropy of H+ ion solution at 298 K is zero, then the entropy of other solutions which have less entropy than H+ will have negative entropy. But entropy is defined as the amount of ...
Hitesh's user avatar
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1 vote
1 answer
56 views

Describing exothermic and endothermic processes using internal energy instead of enthalpy

IUPAC (https://goldbook.iupac.org/terms/view/E02269) defines exothermic and endothermic reactions using the sign (positive or negative) of the change in enthalpy of the reaction, which I think is ...
bluesky's user avatar
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0 votes
1 answer
41 views

How is the Joule-Thomson coefficient related to the increase in temperature of the valve connecting bike pump to tire after pumping?

I was watching this lecture about enthalpy from a thermodynamics course (MIT OCW, 5.60, lecturer Moungi Bawendi). The lecturer goes through experiments and calculations to determine the coefficients (...
xoux's user avatar
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-3 votes
0 answers
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Gibbs free energy ( condition)

I want to derive Gibbs Free Energy formula from 1st and 2nd law of thermodynamics. I saw some texts using T and P constant in derivation. I am confused about that. If n,P, T are constant then its ...
Himalayan's user avatar
-3 votes
1 answer
43 views

Is there a homogeneity issue when two gases are mixed and filled in a vessel? [duplicate]

When two gases (one light and one heavy) are mixed in a 36m3 vessel (mole ratio 6.5%) is there a concern about the homogeneity of the gases (101 psi)??
Clinton Johnson's user avatar
3 votes
3 answers
153 views

Work done by using PV graph

One mole of an ideal monoatomic gas is subjected to changes as shown in the graph. What will be the magnitude of work done, in Joules? I know that work done $=$ area inside cyclic process Therefore, ...
Haider's user avatar
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0 answers
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Does the relation between ΔG° and K vary based on how they are changed?

From the equation ΔG° = ΔH° - TΔS°, I have always been taught that with +ΔH° and +ΔS°, the reaction would be favorable in cases with high temperatures and with +ΔH° and -ΔS°, the reaction would be ...
ptatoe's user avatar
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5 votes
1 answer
60 views

What is the particle speed in liquids at an average room temperature (20-25 degrees celcius)?

I've been searching online for ages and I can't find anything related to this, everything seems to be about gas particles relating to temperature. I'm investigating simple chemistry related to ...
Abigail Mckinnon's user avatar
5 votes
1 answer
94 views

Relation between dilution and osmotic pressure

The following question is taken from IAT 2024, an entrance test for research institutes in India at the high school level: Which one of the following plots correctly describes the variation of ...
Aadhaar Murty's user avatar
2 votes
1 answer
74 views

Entropy and Internal Energy in irreversible adiabatic process

I have a question related to title. Please see the following discussion: In an irreversible process: $ΔU_\mathrm{irr} = q_\mathrm{irr} + w_\mathrm{irr}$ $ΔU_\mathrm{rev} = q_\mathrm{rev} + w_\mathrm{...
user146901's user avatar
-1 votes
1 answer
31 views

If the electron affinity for a neutral element is positive (i.e. endothermic process), is the anion more stable than the neutral atom (at STP)?

This might be a bad question, but I have to ask because I'm finding conflicting answers online. Let's say that I have the following reaction: $$O + e^-\rightarrow O^-$$ While I understand that the ...
Chitraksh Pandey's user avatar
-4 votes
1 answer
74 views

What is the reason behind atoms/molecules in reversible reactions reverting back to its reactant state even if they have found stability? [closed]

If atoms and molecules aim for stability and equilibrium, then why do they feel the need to revert back into their original state once they have already found stability? Example: $\ce{I2 + H2 \to 2HI}$...
Yoojin's user avatar
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-1 votes
1 answer
71 views

Is heat a state function when we consider an isobaric process in a closed system? [closed]

Consider a hydrostatic thermodynamic system, ie a $PVT$-system. We have internal energy differential $$dU=TdS-PdV+\mu dN\tag{1a}$$ $$=dQ-PdV=\mu dN\tag{1b}$$ and enthalpy differential $$dH=d(U+PV)\tag{...
xoux's user avatar
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1 vote
1 answer
65 views

Theoretical justification for the definition of standard enthalpy of reaction

I've been reading the book Chemistry: Core Concepts by Allan Blackman, Daniel Southam, Gwendolyn Lawrie, Natalie Williamson, Christopher Thompson and Adam Bridgeman. They give the following definition ...
russell.price's user avatar
-1 votes
1 answer
63 views

Standard enthalpies of reactions involving multiple gases as reactants

I'm confused by the definition of standard enthalpy of reaction. Consider a reaction which has multiple gases as reactants, such as the one below which shows the combustion of methane. $$\ce{CH4 (g) + ...
russell.price's user avatar
2 votes
2 answers
1k views

Why does entropy increase on mixing two ideal liquids?

Why does entropy increase when we mix two ideal liquids? In my opinion entropy shouldn't change. Say we have two beakers of equal volume filled with $\ce{H2O(l)}$. I mark them red and blue (the ...
Gauransh's user avatar
0 votes
2 answers
150 views

Mathematical proof that more work is done in an isothermal than an adiabatic expansion? [closed]

Work in an isothermal process is expressed as $$W=-\int_{V_0}^{V}\frac{nRT}{V}dV=-nRT\int_{V_0}^{V}\frac{dV}{V}=nRT\ln\left(\frac{V_0}{V}\right)$$ while work in an adiabatic process is expressed as $$...
NH261108's user avatar
2 votes
1 answer
48 views

Isobaric expansion vs Isobaric Free Expansion [closed]

Our teacher while teaching thermodynamics talked about free expansion, isothermal free expansion and adiabatic free expansion. But for isobaric free expansion, he said that's not possible (it's not a ...
Slater's user avatar
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0 votes
2 answers
107 views

Finding the point where reaction switches from endothermic to exothermic

One mole of monoatomic gas undergoes a linear process A to B shown in P-V diagram. Volume of gas from where process turn from an endothermic to an exothermic is? I tried to calculate the point where ...
JackSparrow's user avatar
1 vote
1 answer
195 views

Standard Enthalpy of Formation of Refrence state(A consequence or assumption) and H+(aq)

Ok, this has been bugging me for a while now. Our teacher taught us that the standard enthalpy of formation of the reference states of elements is "assumed" to be zero. However, I've read in ...
Ayush Naman's user avatar
1 vote
2 answers
114 views

Equation of state for gas and liquid

If I'm correct, one and the same EoS is used for both liquid and gas phase. I'm trying the classical Peng-Robinson equation to get pressure from temperature and density: when using values for the gas ...
Mariner's user avatar
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0 votes
1 answer
107 views

Closest attempt to making a Carnot Engine [closed]

My professor, a firm believer in electric cars, and I have engaged in a debate regarding the convenience of internal combustion engine(ICE) based vehicles in today's economy, (especially in my country)...
Ronith's user avatar
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-1 votes
1 answer
87 views

Enthalpy of reaction with equal amounts of gaseous products and reactants

At a constant pressure and temperature the enthalpy change for a reaction (assuming ideal gas law) is given as $$\Delta_\mathrm{rxn}H = \Delta n_\mathrm{g}C_pT,$$ where $\Delta n_\mathrm{g}$ is the ...
Unlogical Chymist's user avatar
4 votes
2 answers
339 views

Calculating the heat of reaction between sulfuric acid and sodium hydroxide

For my lab report I have to calculate the theoretical heat of reaction $\Delta H_{\text{rxn}}$ between sulfuric acid $\ce{H2SO4}$ and sodium hydroxide $\ce{NaOH}$ using their heat of formations. The ...
user10059620's user avatar
7 votes
2 answers
1k views

Author claims that for an ideal gas dU/dV=0

I'm currently reviewing Ball's physical chemistry in preparation for the physical chemistry ACS exam. On page 47 he makes the claim that $ \frac{\partial U}{\partial V}|_{T}=0 $ for an ideal gas. This ...
JWWigfield's user avatar
0 votes
0 answers
51 views

Change in Gibbs energy for lithium redox reaction

I was reading an electrochemistry book by Thomas F. Fuller, in this book the thermodynamic values for the lithium redox reaction at standard conditions are the following: Reaction $\Delta G^o$ [kJ/...
STOI's user avatar
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4 votes
1 answer
101 views

Gibbs energy of an imperfect crystal

Our materials professor likes to do Kahoot quizzes and I am confused about why the following statement is true: A defect in a crystal gives it higher energy. I know that an imperfect crystal has a ...
Christian's user avatar
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-2 votes
1 answer
69 views

Two different approaches for calculating enthalpy change for methane + HCl

I know that $\Delta{H}=H_{products}-H_{reactants}$ and also we can use $\Delta{H}=\Sigma{H}_{bonds broken}-\Sigma{H}_{bonds formed}$. Take the example of methane + HCl. If you calculate the total ...
b20's user avatar
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-2 votes
3 answers
102 views

Why do we have water vapor at room temperature and atmospheric pressure when water is a compressed liquid at these conditions?

At room temperature and 1 atm pressure liquid water should be a compressed liquid. Now if that is the case then why do we have water vapor at these conditions? I can't make sense of this based on just ...
chem_101_102's user avatar
1 vote
0 answers
39 views

Strain energy, binding affinity, penalties in protein-ligand interactions

I am not sure I understand the concepts of penalties and the relationship between strain energy and binding affinity in protein-ligand interactions. I was reading that strain energy can be calculated ...
WithSci's user avatar
  • 111
-1 votes
2 answers
57 views

The correct way of formulating change in enthalpy

I came across this question: One mole of a non-ideal gas undergoes a change of state $(2.0 atm, 3.0L, 95K)$ to $(4.0 atm, 5.0L, 245K)$ with a change in internal energy = $30L atm$. Find the change in ...
DriftAsimov's user avatar
0 votes
1 answer
67 views

ACS physical chemistry question about internal energy

$$\ce{A(s) + 2B(g)->2C(s) + D(g)}$$ $\text{d}U$ at standard state conditions is measured at a temperature $T$ in a constant volume calorimeter. $\text{d}H$ at standard conditions is approximately: ...
JWWigfield's user avatar
1 vote
1 answer
60 views

Could the presence of multiple stabilizer oxides induce sluggish diffusion in a stabilized zirconia to increase lifetime?

The presence of yttria stabilizes zirconia's high temperature allotropes, but it also decreases the lifetime due to more defects that can induce more diffusion into yttria rich and poor regions, ...
user145034's user avatar
3 votes
1 answer
113 views

Effect of Pressure on the Position of Equilibrium

The following general reaction proceeds with decrease in amount of substance, so increasing pressure should shift the position of equilibrium to the right. $$\ce{2 A(g) <=> B(g)}$$ But let's say ...
Muhammad Ali's user avatar
-5 votes
1 answer
72 views

Why are internal energy and work mentioned in a question about exothermic or endothermic systems? [closed]

This is a question from my chemistry homework. Note the explanation below. A 100.0-g bar of gold is heated from 25°C to 50°C during which it absorbs 322 J of heat. The volume of the gold bar remains ...
Shay's user avatar
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0 votes
3 answers
91 views

Entropy change during rusting of iron [closed]

In my book I have a solved question: $$\ce{4 Fe(s) + 3 O2(g) -> 2 Fe2O3(s)}$$ For that reaction: $$\Delta H=-1648\ \mathrm{kJ/mol},\ \Delta S=-549.4\ \mathrm{J/(K\ mol)}\ \text{at}\ 298\ \mathrm K$$...
Pankaj's user avatar
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-1 votes
1 answer
51 views

Entropy changes of system/surroundings in irreversible adiabatic process [closed]

I recently came across a statement in a test which said "Neither reversible nor irreversible adiabatic process can cause a change in entropy of surroundings". This statement was given to be ...
Yes's user avatar
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1 vote
1 answer
46 views

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}...
Eric Brown's user avatar
0 votes
0 answers
51 views

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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1 vote
1 answer
88 views

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
3 votes
3 answers
184 views

Why is there no work in a free and adiabatic expansion of a gas? [closed]

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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3 votes
1 answer
95 views

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, ...
David's user avatar
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0 votes
0 answers
40 views

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 ...
Ocean1's user avatar
  • 11
3 votes
3 answers
1k views

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
  • 159
0 votes
1 answer
126 views

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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4 votes
0 answers
100 views

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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