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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How do you know if a fatty acid or something else that's amphipathic will form a micelle or a phase separation in aqueous solution? [on hold]
Or do all fatty acids just always form micelles, and only hydrophobic compounds form phase separations?
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0answers
20 views
Thermodynamics - linking Gibbs free energy, enthalpy and entropy [on hold]
I wanted to write an expression for the entropy change of a reaction
Would I use ΔG = ΔH - TΔS OR ΔS = - ΔH/T I don't get the reason for these two different equations. Is the later for ...
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1answer
34 views
Calculating equilibrium constant with Gibbs's Free Energy [on hold]
Use data from Appendix C in the textbook to calculate the equilibrium constant, $K$, at $\pu{298 K}$ for each of the following reactions:
$\ce{H2(g) + I2(g) <=> 2HI(g)}$
$\ce{C2H5OH(g) <=&...
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0answers
23 views
How to calculate relations among thermodynamic quantities
I'm trying to learn how to calculate the many relations that exist in thermodynamic. Like for example
$$ \left(\frac{\partial U}{\partial S}\right)_V $$ or $$ \left(\frac{\partial S}{\partial T}\...
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1answer
50 views
Interpretation of H as T goes to absolute zero
Euler's identity for the enthalpy states that (for a single component and phase)
$ H = TS + \mu N$
What are the implications of this expression in the context of the third law of thermodynamics (...
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21 views
4
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3answers
70 views
Is there a thermodynamic driving force for racemisation?
Why does racemisation occur?
My doubts are:
Is it due to entropy?
If it is due to entropy, how is the reduction of optical activity by racemisation a consequence of increased thermodynamic ...
0
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1answer
100 views
Why do we use pV term independent of U in the equation H = U + pV? [duplicate]
I have read the following definition of enthalpy in my textbook:
A substance has to occupy some space in its surroundings depending upon its volume ($V$). It does against the compressing influence ...
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1answer
24 views
Why is the equilibrium constant being calculated differently here?
In my NMR textbook, it says the equilibrium constant for a dynamic process (e.g., A in equilibrium with B) is calculated by the concentration of A divided by the concentration of B. Is this a typo? ...
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1answer
26 views
Are specific heat capacity and boiling point of a substance related or proportional to each other?
That is, if the substance has a high specific heat, will it also have a high boiling point? ( and vice versa)
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0answers
32 views
Expression for the entropy of an ideal gas
I want to obtain the Sackur-Tetrode expression for the entropy of an ideal gas based on:
$$S = K_B ln \Omega$$
We have an isolated system with a fixed volume V and fixed number of particles
N and ...
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1answer
44 views
What is the substance with the highest specific heat?
I always learned that water has the highest specific heat, but I recently saw that Hydrogen has a specific heat as high as 14 cal/gC and helium has a specific heat of 5 cal/gC, which would be much ...
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1answer
47 views
Understanding the partial derivative of temperature with respect to thermodynamic beta (coldness)
I am trying to prove that the specific heat is related to the fluctuations in the energy:
$$c_V = \frac{\langle E^2 \rangle - \langle E \rangle^2}{k_\mathrm BT^2}$$
Where:
$$\beta = \frac{1}{k_\...
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1answer
24 views
In chemistry what do they mean by disorder when in the context of entropy?
Entropy is often the amount of disorder is present in a system, but when they refer it to the degree of disorder in a system what do they mean. It just seems the term is quite vague and not very ...
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2answers
28 views
What is the reason behind electron transition in the flame test
I am a beginner in this topic but I am aware that when flame test (for alkali and alkaline earth metals) is done there is a s-s transition of electrons from the ground to their excited state.
But I ...
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2answers
50 views
Intuituve reason for the constant of proportionality 2/3 in pv=nRT=(2/3)U
Why is there a $\frac23$ term?
I fully understand that it makes sense for pressure to be the volume weighted average kinetic energy. And the equation above shows that this is so (for an ideal gas). I ...
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1answer
37 views
Doubt from Thermodynamics [closed]
If we have to make graph for reversible adiabatic process involving an ideal gas in a P - T curve then how to proceed ?
My try : As we know the relation between P and T in Adiabatic process , ...
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1answer
33 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 $\pu{13.33 ^\circ C}$...
2
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1answer
48 views
What is the topology of a phase diagram?
This question is cross-posted from phys
Looking at various two-variable phase diagrams I was struck by that on every one I have seen so far all the phases formed simple connected regions; see, for ...
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1answer
57 views
thermochemistry problem confusion
I can understand upto where the ideal gas equation is used to calculate volume of steam. But on trying to find out $ \Delta V$ , i saw that there are no gases on the reactant side so then $P\Delta V=(\...
1
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1answer
30 views
How do you figure out fuel specific impulse non-experimentally?
Simple question, probably very complicated answer:
Without building a test engine/rocket and finding out experimentally, that is to say, based on chemical characteristics alone, how can one compute ...
1
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0answers
37 views
How does degree of freedom work [closed]
I understand that the degree of freedom is the number of ways in which a molecule can acquire energy. I don't want you to explain the definition, but I want to see how it works. Please explain how is ...
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1answer
46 views
Insoluble salts and Gibbs free energy
Is it true that according to gibbs free energy equation, insoluble salts such as AgCl don't dissolve because the process would be too endothermic? The right side of the equation, TΔS, would have to be ...
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1answer
28 views
What is the meaning of K in the thermodynamic equation for equilibrium constant?
I just studied the formula for equilibrium constant in thermodynamics. But when an equilibrium is established $\Delta G$ is always $0$ as told by my teacher. Then $k$ has to be always $1$ whenever an ...
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0answers
13 views
Is Sorption process for salt (using environmental moisture) an exothermic process?
Consider a sealed container $C$ with pure water vapor (i.e. there is no air just water vapors) inside it at 100% relative humidity. The temperature of the container walls is $t_0$ degrees Celsius. Now ...
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1answer
114 views
Why is everything confused up in thermodynamics [closed]
Is the formula application done properly when calculating work. I think the volume should be final minus the initial. So in first step it should be $V_1-V_i$ and in second step it should be $V_f-V_1$. ...
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1answer
39 views
Does the translational part of internal energy mean the kinetic energy of the gas?
Internal energy of an ideal gas consists of energy due to translational, rotational , vibrational etc.
This line from WP says:
In thermodynamics, the internal energy of a system is the energy ...
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2answers
58 views
Why does ATP has a lower entropy than ADP
I was confused about why ATP has a lower entropy than ADP when ATP has 1 more phosphate group. According to https://chem.libretexts.org/Textbook_Maps/Biological_Chemistry/Metabolism/ATP%2F%2FADP#...
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0answers
25 views
Temperature differences within static water bath
My question is how much temperature difference could there be between two temperature sensors ~1cm apart in a static water bath, assuming that the sensors are of similar thermal mass?
The reason for ...
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0answers
36 views
does adding water to water release heat/increases temperature of water
Multiple sources as mentioned below says formation of bond releases energy including hydrogen bond .So i was wondering, as hydrogen bonding is present in water so when you add water with water would ...
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1answer
42 views
Why is the equilibrium constant unaffected by a change of the initial concentration?
In my class, it was taught that the equilibrium constant does not vary with
the intial concentration of the reactants? Why is it so?
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1answer
31 views
An equal amount of hydrogen gas is dissolved in a 1L vessel and a 2L vessel, both filled with water. Which vessel has higher entropy? [closed]
This question came up in our chemistry class and we could not determine which would have the higher entropy. Clearly, Vessel 2 has a larger volume, but Vessel 1 has a higher concentration of $H_2$. ...
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0answers
10 views
If a reagent in a metabolic reaction has a gas and an aqueous form, which one to use when computing Gibbs energy of reaction?
In many cases, the chemical reactions catalyzed by cells involve chemical species having a gas form and an aqueous form (eg: CO2, O2, CH4). The Gibbs energy differential of a chemical reaction greatly ...
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1answer
80 views
Why do gases coexist as liquid and vapour?
I have having difficulty in understanding the liquefaction of gases.In the graph
of isotherms of $\ce{CO2}$ I cannot understand how can gas coexist as liquid and vapour under area of $\mathrm{XCEBY}$....
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2answers
57 views
Help understanding the pressure's effect on equilibrium and Le Chatelier's principle [closed]
So let's say we have a closed system in the following reaction:
$\ce{N2O4 -> 2 NO2}$
The only way to increase the system's pressure without adding any mole of gas and keeping temperature constant ...
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1answer
68 views
Why are combustion reactions spontaneous? [duplicate]
I learned that spontaneous reactions are reactions whose activation energies can already be overcome with the temperature they're already in. Since the temperature they're in already provides enough ...
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0answers
34 views
Thermodynamics of exo/endothermic reactions
Complete chemistry newbie here, hi. Sorry if I ask a stupid question, but I wonder what does exo/endothermic means from a thermodynamical point of view.
Considering that temperature (a macrostate) ...
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0answers
34 views
Freezing water droplets with liquid nitrogen vapor
I have an idea for a device but I'm not sure about the thermodynamics.
Would liquid nitrogen vapor (not liquid) be cold enough to instantly freeze a spray or mist of water? I know water freezes at 0 °...
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1answer
51 views
Expansion work by a gas when pressure is not explicitly constant?
How is it possible to calculate the work done by a gas when pressure is not explicitly stated to be constant? The question states:
Calculate $\Delta H$, $Q$, and $W$ when $1\ \mathrm{mol}$ of He ...
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1answer
54 views
Entropy change during flow of heat
If heat $Q$ flows from the surrounding nature temperature at $T_\text{surr}$ to the system at temperature $T_\text{system}$, then $$\Delta S_\text{total}=\frac{+Q}{T_\text{system}}+\frac{-Q}{T_\text{...
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1answer
36 views
Current in a Lithium Ion Battery
I am trying to find the current transferred to the anode and cathode of a Lithium Ion Battery at different voltages. I know the temperature (approximately) of the battery, the battery's starting ...
5
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1answer
268 views
Why does ozone have higher entropy than oxygen?
$$\ce{3O2(g) -> 2O3(g)} \qquad \Delta H^\circ (\pu{298 K}) = \pu{+142 kJ mol^-1}$$
Since the RHS of the equation contains less number of gaseous molecules, naturally I expected the $\Delta S$ to ...
3
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1answer
108 views
Why is the Kelvin Temperature Scale Based on the Triple Point of Water?
Why would the Kelvin temperature scale not just be based on the freezing point of water, which is only .01 degrees Celsius off from it? Is this just a more accurate way of measuring and quantifying ...
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1answer
52 views
How many watts would I need to get CO2 from 30 °C to 4000 °C in 1 hour
Scenario: After reading some articles on new sorts of ways to deal with $\ce{CO2}$ in the atmosphere, a question came to mind: If I had 100 kg of $\ce{CO2}$, and I would like to heat it up from 30 °C ...
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1answer
104 views
should charge balance be based on activities?
We have a fluid with $\pu{0.01 M}~\ce{HCl}$ and $\pu{0.02 M}~\ce{K2HPO4}$, so if we assume activity coefficients are $1$ throughout we can find pH as $6.800012$ and confirm that at that pH there is ...
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2answers
70 views
Doesn't the isothermal irreversible expansion/compression of an ideal gas law violate the ideal gas law? [closed]
Let's say a cylinder has some ideal gas. We use a piston to suddenly expand the gas in isothermal condition from $1\ \mathrm{atm}$, $20\ \mathrm L$ to $0.5\ \mathrm{atm}$, $50\ \mathrm L$.
Since the ...
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1answer
63 views
Expression for fugacity coefficient derived from a pressure-explicite EOS
In the book, Thermodynamics for Process Simulation, the authors propose to derive an expression for the fugacity coefficient from a pressure-explicit equation of state, as an example among many others....
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2answers
33 views
Is water vapour formation possible at -10 degree celcius?
Under any pressure conditions is it possible ? If not then is there no water vapour present in places where temperature drops to -10 degree celcius ?
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48 views
Is the concentration of water included in the acid disscociation constant? - Wikipedia confuses me
I refer to the following wikipedia article
https://en.wikipedia.org/wiki/Acid_dissociation_constant
Header paragraph: Equilibrium constant.
First the equilibrium constant is given in terms of ...
1
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0answers
57 views
Gibbs Free Energy: Exothermic, low temperature & reduced system entropy - such reaction is spontaneous or not?
According to $\ce{\Delta G^\mathrm{o}= \Delta H^\mathrm{o} -T\Delta S^\mathrm{o}}$, if a reaction
a) is exothermic,
b) reduces system entropy, and
c) the temperature is low,
then it is spontaneous....
