# 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.

1,854 questions
Filter by
Sorted by
Tagged with
15 views

### How to calculate the molar entropy of different substances at different temperatures?

I want to calculate the Gibbs free energy of ammonia synthesis at around $\pu{700K}$, but I can't seem to find the entropy values at that particular temperature. Is there a formula to calculate the ...
22 views

### Can dissipative work be circumscribed as irreversible heat transfer

My question refers to an article I read yesterday in which the author states that for the calculation of the entropy change for a process (in that case friction, during an irreversible adiabatic gas ...
37 views

### Hydrogen disulfide heterogenous equilibrium

I have been struggling with the following problem for quite a while: I was able to calculate the Gibbs free energy and the equilibrium constant, using the formula $$ΔG = -RT\ln K$$ and ...
62 views

### Heats of formation of neutral molecules and homolytic vs heterolytic bond dissociation in mass spectrometry

I am currently studying the textbook, Mass Spectrometry, third edition, by Jürgen H. Gross. Chapter 2.4.3 Bond Dissociation Energies and Heats of Formation says the following: Great efforts have ...
16 views

### How to find out the vapour pressure dependence on temperature and what is meant by thermodynamically consistent? [closed]

The Antoine equation often is used to describe vapor pressures: lnPσ = A − B /(T + C). For temperatures near the normal boiling point: a. Derive an expression that gives the behavior of ∆Hvap as a ...
49 views

### Does dissociation of molecules into atoms change the volume of mixture?

For example, if $\ce{H2}$ is converted to two $\ce{H},$ does the volume of the mixture change? If it doesn't, does it imply that the work done is $0$ because work is $P\,\mathrm dV?$
65 views

### Why doesn't nitrogen react with oxygen at room temperature?

I already know that nitrogen's triple bond requires a lot of energy to be broken, so the activation energy is very high, but the book also lists the endothermic energy change as a reason. Does the ...
69 views

44 views

### Delta G in an equilbrium reaction(forward and backward)

Consider a reaction say $$\ce{A + B <=> C + D}$$ Now $\Delta G$ for the forward reaction is: $$\Delta H - T\Delta S$$ For the backward reaction $\Delta H$ and $\Delta S$ are clearly the same ...
134 views
+50

### What is the precise definition of standard molar entropy?

I understand what the standard molar entropy is, and how to use it in calculations, but I'm interested in understanding exactly how it's defined and measured. My recollection from a long time ago is ...
49 views

### Equation of water at triple point

I was thinking about what exactly happens at the triple point of water, and what could be the effect of adding solutes/solvents. I feel we can represent the triple point using the following ...
46 views

### How to determine the formula for calculating the enthalpy change of a reaction? [closed]

$$\ce{4 HCl(g) + O2(g) -> 2 Cl2(g) + 2H2O(g)}$$ In the reaction above, knowing the enthalpy of formation of each individual compound, in order to calculate the standard enthalpy change of the ...
39 views

### Euler's Theorem and Extensive properties

I read in a textbook (Mathematics for Physical Chemistry by D. McQuarrie) an example of Euler's Theorem used in Thermodynamics. The author states "The [variables] are all extensive [quantities], and ...
54 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 ...
56 views

### Why is concentration used as a proxy for activity instead of mole fraction?

I am trying to understand how the Gibbs energy change of a chemical reaction is computed and I do not understand why concentrations (mol/L) are used as a proxy for activity rather than mole fractions (...
43 views

### Which of the following reaction will have greater enthalpy and why? [closed]

Which of the following reaction will have greater enthalpy and why? $\ce{C (g) + 4 H (g) -> CH4(g)}$ (reaction enthalpy = $x\ \mathrm{kJ/mol}$) $\ce{C (graphite) + 2H2 (g) -> CH4 (g)}$ ...
19 views

### Internal energy of reversible, adiabatic expansion

I have come across something in our answer key that I don't agree with or perhaps have misunderstood and would appreciate if someone could tell me if I am correct or not. For a reversible and ...
49 views

### Are there reactions operated at high temperature at industrial level? [closed]

Temperature is an important parameter when you deal with a chemical reaction, first of all $\Delta G$ and $\Delta G^\circ$ depend on temperature, and as a consequence the spontaneity of a reaction ...
118 views

### Kinetics of converting a water + heavy water mixture to HDO

Imagine an initial 50%-50% mixture of normal ($\rm H_2 \rm O$) and heavy water ($\rm D_2 \rm O$). I think, simply mixing them, the result will exponentially converge to an equilibric state, where ...
27 views

### Relating Gibbs Free Energy to Equilibrium Constants [closed]

I am having some trouble relating these two concepts. I know that if K=1 then delta g is zero, and that we can interpret signs and magnitudes. However, i am having trouble determining required ...
82 views

### Need help understanding Enthalpy

My chemistry textbook says that: Enthalpy (Internal Energy) = chemical potential energy + thermal energy Now, I know that Enthalpy and Internal Energy are different so I really don't understand ...
34 views

### Effect of drinking on internal energy and entropy of the universe

I have just been doing some questions on thermodynamics and have come across a strange question that I can't seem to grasp. The question asks me to estimate the change in body temperature as well as ...
21 views

50 views

### Modifications and alterations in the state of chemical equilibrium

Let us consider that we have a mixture of gases, considered ideal, that is in balance. Like, for example, $$3\ce{NO} (g) \rightleftharpoons \ce{N2O} (g) + \ce{NO2}(g)$$ If we consult the ...
35 views

### How do bonds form without violating the second law of thermodynamics [closed]

It might be obvious that entropy related to reactions always increases and I understand (somewhat) why this happens. My question is why if you have two hydrogen atoms in a vacuum without being bonded ...
112 views

### Regarding units of water potential and chemical potential

If water potential is nothing but the chemical potential of a given solution, then why do their units differ? If the unit for the latter is taken as 'Energy per molecule' (which makes sense to me ...
39 views

### Ground state elevation for phase transition

I have a question about the illustration from chem.libretexts.org: the ground states of the liquid and gas are offset from that of the previous state by the heats of fusion and vaporization, ...