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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3answers
108 views

Why does the internal energy increase when ice melts to give water?

Ice melts at 0 °C to give water at 0 °C. The internal energy apparently increases. Thermal energy is transferred to ice causing this to occur. Since the temperature doesn’t change, all the thermal ...
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5answers
2k views

What exactly is temperature?

I've read at many places that temperature is the average kinetic energy of particles present in an object. I just don't intuitively get how kinetic energy is connected with temperature. And how is ...
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1answer
69 views

Calculation of free energy from potential and kinetic energy

I am having trouble understanding how (and even whether it's possible) to get free energy from kinetic and potential energy. I have run molecular dynamics simulations (NPT ensemble, CP2K software), ...
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1answer
242 views

Extrapolating from a calorimetry lab to find a new delta T with different volumes and grams of substance

So, we just finished an AP chem lab where the question was basically: Given the results of the lab were that $\pu{5 grams}$ of $\ce{CaCl2}$ and $\pu{45ml}$ of water produced a $\pu{13.33 ^\circ C}$...
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A Thermodynamics question involving the molar solubility and Ksp of CaCO3

This thermodynamics question is from my textbook, I am not sure how to solve it correctly and I do not have the answer. The first thing I did was to calculate the number of moles from the Ca(OH)2 ...
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1answer
79 views

Temperature and pressure for three phase equilibrium of aqueous sodium chloride solutions

I am currently investigating the effect of adding Salt(NaCl) to water on its triple point. Let us assume the mass ratio of water to NaCl is $1:1$. I asked a similar question previously. But, I still ...
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0answers
31 views

Can there still exist equilibrium with a very high equilibrium constant?

Problem Consider the reaction translated by: $$\ce{2 CO(g) + O2(g) <=> 2 CO2(g)} \quad K_c = 2 \times 10^{22}~\text{at } \pu{1000 K}$$ The order of magnitude of the equilibrium constant, $K_c$,...
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1answer
88 views

How does the entropic force arise within the hydrophobic effect?

I know that the hydrophobic effect is usually explained by the entropic effect originating from the disruption of hydrogen bonds between molecules of water and the nonpolar substance. The hydrogen ...
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1answer
62 views

Description of a van't Hoff apparatus

A "van't Hoff apparatus" is mentioned as a means of performing a reaction involving gases in a reversible manner, for instance here. Unfortunately I have been unable to find a description of such a ...
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3answers
89 views

Reversibiliy and equilibrium

My textbook states "A system is in thermodynamic equilibrium if it is in Thermal, Mechanical, and chemical equilibrium simultaneously". The Wikipedia article on "reversible processes&...
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1answer
12k views

Equation to calculate the triple point

Is there any equation that can calculate the triple point of a substance? Because a method for calculating the critical temperature and the Boyle temperature of a substance that I posted in another ...
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2answers
285 views

Difference between ΔQ and dQ [closed]

What is the difference between $$\Delta Q$$ and $$\mathrm dQ$$ in thermodynamics? I think one is used when the change is very small and the other with bigger changes, but I am not sure.
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What is the enthalpy change of neutralisation of vinegar (diluted acetic acid) and calcium carbonate?

If anyone has conducted an experiment that determined this value or knows reliable sources that show the literature/thereotical value of this enthalpy change, please share your answer. Thank you very ...
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1answer
50 views

Change in Entropy and Spontaneity [closed]

I was studying thermodynamics and got stuck with some questions. I am pointing them down. I have studied that $\Delta S_{\text{total}}$ accompanied by a spontaneous process is greater than 0. But is ...
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1answer
54 views

Rigorous reason behind internal energy change being zero while mixing

A container is divided in two parts: one part contains oxygen gas $(n_1$ moles, at temperature $T_1)$ and the other part contains helium gas $(n_2$ moles, at temperature $T_2).$ The partition ...
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3answers
131 views

Why water cools from outside to inside?

It is a well-known fact that Water kept in a container, on cooling, results in freezing with initially at the circumference of surface (1D), then on the surface (2D) and then throughout the volume (...
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0answers
30 views

When, if ever, can standard enthalphy be subsituted for standard chemical potiential?

I'm reading through a combustion modeling paper by Gordon & McBride which is a bit scant on some of the algebra & calculus used to derive their equations. My advisor and I have derived nearly ...
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1answer
80 views

Apparent paradox regarding spontaneity

Consider the following analysis ( rev and irrev respectively refer to a reversible and an irreversible path, between the same initial and final states): $dU_{rev}=dq_{rev}+dw_{rev}$,and,$dU_{irrev}=...
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2answers
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Stoichiometric defects in silver bromide

Stoichiometric defects (Schottky and Frenkel defects) in ionic crystals are formed due to irregularities in the ionic arrangement which maintain the stoichiometry and electroneutrality of the solid. ...
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2answers
28 views

Crossing at critical temperature of a gas

This is written in the book 'Treatise on Thermodynamics' by Max Plank- the crossing of the critical temperature at any pressure other than the critical pressure differs in no way from the crossing of ...
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2answers
53 views

Positive work in the Carnot cycle

In the Carnot cycle the overall work done on the piston is positive. I am having trouble with the real meaning of that. Does positive work mean the piston is moved up and has, over the course of the ...
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1answer
50 views

Thermodynamic model of inclusion process of alpha-cyclodextrin

I have a question about thermodynamic model of inclusion process of CD, published by Tabushi (DOI: 10.1021/ja00471a043). Here, in 3rd step, action is described as: "An apolar solute (guest molecule) ...
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1answer
66 views

Vapour Pressure of A Solution

I study in class 12, and have a doubt in vapour pressure that my school teacher and my friends are not able to clarify. My doubt is the reason why the partial vapour pressure of each individual ...
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1answer
27 views

Can more than one thermodynamic process occur at the same time? [closed]

Thermodynamic processes I know about are, Isothermal, Adiabatic, Isochoric and Isobaric (if you know any other, please mention). Is it possible that any 2 or more of these four processes occur ...
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0answers
42 views

Chemical Potential in the Fluorescent Molecule

I'm reading this paper, which states that the chemical potential $\mu$ is determined by the steady-state balance of up and down transitions in a fluorescent molecule. I am happy with this ...
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3answers
4k views

How can a thermometer ever show the actual temperature of an object if the object loses heat to the thermometer?

We know that when two objects are placed in contact with each other, after a period of time, the two objects will have the same temperature. Thus, if a hot body comes into contact with a relatively ...
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2answers
3k views

How to derive the relation between gibbs energy and equilibrium constant?

I want to understand the derivation between gibbs energy and equillibrium constant $$\Delta G=\Delta G^o+RT\ln Q?$$ I have seen a similar post on CSE Derivation of relationship between equilibrium ...
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2answers
46 views

Exothermic dissolution

When I was learning about salts that show exothermic dissolution, I noticed that the same salts used in Daniel Cell( due to similarity of size of anion and cation) were undergoing exothermic ...
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1answer
253 views

How is a phase equilibrium defined for a one-component system?

A question on this site asked whether a one-component system is at equilibrium when melting or boiling, and the disparate answers were somewhat dependent on the definition of phase equilibrium. ...
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0answers
32 views

Hydrophobic interactions and Gibbs Free Energy [duplicate]

I want to understand the basis of the hydrophobic effect. In biochemistry, protein structures are often explained in terms of hydrophilic and hydrophobic effects. The hydrophilic interaction is ...
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1answer
34 views

What's the correct definition of activity? [closed]

I learned activity equals 'activity coefficient' times 'mole fraction' but i also learned it equals 'activity coefficient' times 'partial pressure / standard pressure (1bar)'. But there's something ...
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1answer
64 views

Heat capacity of a calorimeter

Why do we mix water with different temperatures to calculated the heat capacity of the calorimeter? Why can't we calculate it directly using just warm water? Asked differently, would the following be ...
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1answer
34 views

Finding heat of formation

The heats of combustion of $\ce{C_xH_y}$, $\ce{C}$, and $\ce{H2}$ are $a, b,\text{and } c$ cal respectively. The heat of formation of $\ce{C_xH_y}$ will be: The answer is $-\left(x b+\frac{y c}{2}-a\...
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1answer
32 views

Is entropy of surroundings a state function?

It is a pretty common well known fact that the entropy of a system is a state function ie. it doesn't depend upon the path taken by the process as long as the initial and final states are the same. I ...
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1answer
67 views

What's the minimum amount of energy needed to remove CO2 from the atmosphere?

I've been learning about CDR (Carbon Dioxide Removal) techniques to combat climate change. These all seem to involve extracting $\ce{CO2}$ from the atmosphere and converting to a mineral, which is ...
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5answers
103k views

Difference between exothermic and exergonic

In High School I learned that an exothermic reactions releases energy, while an endothermic reaction needs energy to occur. Now I learned that there is a separate, somewhat similar classification ...
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1answer
36 views

What is the reason that ice melts with increasing pressure at constant temperature (revelation)?

I've seen many explanations regarding this topic where they explain it in the sense of the anomalous expansion of water, but I actually want an answer where I can understand the different forces at ...
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0answers
27 views

Dependence of Heat Capacity on Temperature

I was studying about the graph of dependence of heat capacity on temperature. As you can see in this picture, heat capacity with constant volume increases near 0K. As the temperature keeps rising, it ...
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1answer
84 views

On the origin of Gibbs Free Energy

It is intuitive to me that for a spontaneous process involving any system i.e. one occurring without constant human interaction $$ \text{d}S \geq 0 $$ as I can observe increasing energy dispersal in ...
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1answer
44 views

Is constant pressure heat capacity = entropy during adiabatic reversible expansion of perfect gas?

For any process, ∆G = ∆H - ∆(TS). Apply this on reversible adiabatic expansion of perfect gas, since the entropy of system does not change during this process, S is constant so ∆G = ∆H - S∆T The ...
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0answers
48 views

Is entropy maximum in equilibrium?

Usually, in the context of non-equilibrium thermodynamics, it is said that entropy achieves a maximum in equilibrium, so the Taylor series expansion of entropy around the equilibrium state as a ...
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1answer
115 views

Enthalpy of reaction between ammonia and oxygen

I have to ask this here because I asked literally everybody I know and I still disagree with them. Using the information in the table below, calculate the heat of released from the following ...
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1answer
76 views

A Curious (definitely wrong) result of Absolute Entropy [closed]

The Gibbs free energy is defined as $$G=H-TS$$ Differentiating both sides $$dG=dH-TdS-SdT$$ For an adiabatic reversible expansion of an ideal gas, we would have $dG=0$, and $dS=0$. Thus we can write, $...
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1answer
1k views

Deriving The Triple Point Temperature and Pressure as the following expression

Using the usual notations of $\Delta H_\text{fus}$, $\Delta H_\text{vap}$, $\Delta H_\text{sub}$, as well as ($T_\mathrm l,p_\mathrm l$) and ($T_\mathrm s,p_\mathrm s$), which corresponds to the ...
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1answer
51 views

Why is maximum work done for reversible paths in isothermal expansion and not minimum work done? [closed]

Work done is given by $W = -P_{ext}dV $ according to convention. Which should mean that in cases of expansion, work done on the system would be negative. If work done is negative, isn't it wrong to ...
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0answers
32 views

Gibbs function for pure substances

I know that the Gibbs function for pure substances is given by $$\mathrm dG = V\,\mathrm dp - S\,\mathrm dT.\tag{1}$$ However, I also saw the same equation in the form $$ΔG = VΔp - SΔT,\tag{2}$$ ...
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2answers
337 views

Apparent contradiction in the type of deviation of an ethanol-water mixture

For a mixture of $\ce{EtOH}$ and $\ce{H2O}$: $\Delta H_{\text{mix}} < 0$ (exothermic) and $\Delta V_{\text{mix}} < 0$ (volume contraction). This means that the unlike interactions are stronger ...
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2answers
83 views

How is a reaction with more products than reactants spontaneous?

If I have a reaction that has $\Delta G^\circ = 0,$ where there are more products than reactants (for example, $\ce{A <=> 2B + 2C}),$ then if I change the concentration of all the reactants and ...
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0answers
30 views

Gibb's energy change for system

Heat liberated by a given amount of an ideal gas is $\pu{1200 cal}$ at $\pu{300K}$. What is the Gibbs free energy change for the gas in this process? My attempt: I know that for a reversible process ...
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2answers
66 views

Is this statement for the First Law of Thermodynamics correct?

My Biochemistry book states the First law of Thermodynamics like this: "The First Law of Thermodynamics states that in a closed system, energy is conserved". My book defines Closed System as a system ...

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