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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Regarding reversible phase transition of a real gas
According to change in entropy for a reversible phase transition, say from liquid to gas at constant pressure $p$ and temperature $T$
: $\Delta S =\frac{\int dq_p}{T} $ which comes out to be $\Delta ...
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How is pumping "Air" into a bicycle make dW (delta work )negative , when in fact there is a increase in pressure and a slight increase in volume? [closed]
Considering that it's an adiabatic process hence $\mathrm dQ=0$, and $\mathrm dU=\mathrm dW$. And since the work is done on the system then $\mathrm dW$ must be positive.
(The answer which is in the ...
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790
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Why is change in internal energy not equal to zero during a phase transition? [closed]
Many books state that when there is no change in temperature $\Delta U$ is equal to zero. Why is this not applicable for phase transitions? I have had this question for a while now and have been ...
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Extrema in free energy of a solution?
I am a high school student reading about the second law of thermodynamics, and one of the equations given was the free energy change in dilution.
$$\Delta G_{\text{dil}} = -RT \log(C_1/C_2)$$
This ...
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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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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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Gibbs free energy where T, V, and P change simultaneously
So $\Delta G = \Delta H - T\Delta S - S\Delta T$.
Is there a way to express $\Delta G$ for a process where T, V, and P change simultaneously only in terms of the initial and final T, V, P? Assume ...
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Ideal Gas equation and its Assumptions [duplicate]
The two assumptions are that the gases are points of mass that move, they have no volume and that there is no interaction between other molecules.
But even the points of mass can collide with each ...
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How can temperature be constant during a reaction? [closed]
So I was reading my textbook about the topic thermodynamics.
Here the second paragraph States that the above equation describes the combustion of liquid ethanol at constant temperature and pressure.
...
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How to calculate the variation of enthalpy in a reaction that does not occur in standard conditions?
Standard enthalpy of formation is a value that represents the enthalpy variation in the formation of compounds with the purpose of using this values to know the enthalpy of a reaction where these ...
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Why thermodynamic state variables of a sytem are only defined at thermodynamic equilibrium and not during any other instant? [closed]
As you have read the title so my question is why are thermodynamic variables only meaningful when the thermodynamic system is in thermodynamic equilibrium and is always meaningless in any other case.
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T∆S implies that heat flows which way?
From Schroeder's Introduction to Thermal Physics.
Parts $(a)$ and $(b)$ are quite simple, and we find that $ \Delta H =-2808\ \mathrm{kJ}$ and $\Delta G =-2879\ \mathrm{kJ}$, so by $\Delta G = \Delta ...
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What is enthalpy? Why do some sources define it as "heat content" of a system? [duplicate]
So after researching thoroughly on multiple different sources about enthalpy (I'm not talking about the equation but the general concept), many credible sources seem to all contradict themselves.
For ...
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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 = $x\ \mathrm{kJ/mol}$)
$\ce{C (graphite) + 2H2 (g) -> CH4 (g)}$ (reaction ...
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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 ...
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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 ...
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How is entropy change defined for a chemical reaction?
I know that:
ds = dq/T for reversible processes.
Can I write change in entropy of a system in which a chemical reaction is happening using this equation. Basically, my question is about whether a ...
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2
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Hess's Law and ΔH
Target equation: $\ce{Mg(s) + 1/2 O2 -> MgO(s)}$
$$
\begin{align}
\ce{MgO(s) + 2 HCl(aq) &-> MgCl2(aq) + H2O(l)} &\quad ΔH &= \pu{-1300 kJ} \tag{1}\\
\ce{Mg(s) + 2 HCl(aq) &-&...
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Change in enthalpy equation [closed]
If the formula for change in enthalpy is ΔH=ΔU+pΔV, and ΔU = q - pΔV then shouldn't the formula be simplified to ΔH = q regardless of whether the volume or pressure is constant? Is this only true when ...
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Heat exchange in adiabatic process
I know my teacher told me that
In adiabatic process there is no exchange for heat between system and surrounding.
Then he came to point. From first law of thermodynamics
$$∆U = q + W \tag{1}$$
...
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Why Gibbs energy change of a process can be negative at constant temperature and pressure? [closed]
This question has been asked before, but the answers are not clear and satisfactory.
If the pressure and the temperature are constant then G would be always zero. How would then G have a value other ...
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Irreversible Adiabatic Process [closed]
While studying about the entropy change of surroundings in irreversible adiabatic process, I came across a sentence.
For infinite reservoir, all processes are considered reversible
And suddenly ...
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Entropy for a closed system [closed]
Case -1
In a free expansion of an ideal gas in a region or container, we cannot trace a pressure-volume path since the pressure, temperature and volume of the gas fluctuate unpredictably when the gas ...
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I was told that the more exothermic the solution, the more soluble the salt. Is this statement wrong?
I was also told that $$\Delta H(\text{solution}) = \Delta H(\text{hydration}) - \Delta H(\text{lattice E})$$
However, for $\Delta H(\text{solution})$ to be exothermic, it has to have a negative value ...
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Why does a NOx container get cold when NOx is released? and What is the relationship of the vapor pressure curve with the liquid-vapor dome?
The temperature at which $\ce{NO_x}$ is in equilibrium with its liquid and vapor phase at 1 atm is about –84 °C. Does that mean $\ce{NO_x}$ exists as a liquid at that temperature? What about it's ...
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What is the reason for phase separation? [closed]
I have seen phase separation as a phenomenon taking place. However I do not understand why this phenomenon occurs as a counter example to the natural laws of diffusion along the concentration gradient....
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Entropy and total differential
In an exercise, I have derived that
$$\mathrm dS_\mathrm{m} = \frac{3R}{2T}\mathrm dT + \frac{R}{V}\mathrm dV$$
using the 1st and 2nd law of thermodynamics (1 mol ideal gas).
Now, I want to write $\...
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What is meant by excess energy in exothermic reaction?
I was reading this article on exothermic reactions online: Exothermic reactions
It states that "In exothermic reactions, the products have less enthalpy than the reactants, and as a result, an ...
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Thermal conductivity and enthalphy data for nitrogen gas
I am struggling to find the data for thermal conductivity and ethalphy of nitrogen gas at reduced pressure (500 mbar). Most of the information is for nitrogen gas at 1 bar or above. Does anyone know ...
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How to determine if a mixing process is spontaneous at constant temperature but variable pressure
This is a conceptual question.
Many times we work with the gibbs energy of mixing under conditions of constant temperature but not pressure.
In a problem like this:
Suppose that 2.0 mol H2 at 2.0 ...
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Work done by gas in isothermal process [closed]
A $20\ \mathrm l$ steel cylinder containing $\ce{N2(g)}$ at $20\ \mathrm{atm}$ and $300\ \mathrm K$ is kept in a big jar containing air at $1\ \mathrm{atm}$ and $300\ \mathrm K$ and sealed. $\ce{N2(g)}...
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Using Hess's law to find molar enthalpy of formation without an initial reaction [closed]
I'm having issues relating Hess's law to this question:
The given chemical equation represent the combustion of ammonia and the combustion of hydrogen
$$
\begin{align}
\ce{4 NH3 + 3 O2 &-&...
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Is there any difference between thermal energy at room temperature in fluids(water) vs air?
Context of the question: I was reading on hydrogen bonds, specifically how close they are to the thermal energy of the fluids. So I googled the value of thermal energy at room temperature, which was $\...
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When an inert gas is added to a system of constant volume, equilibrium is not effected?
But pressure of the system increases. Because of this increase in pressure, wouldn't (according to Le Chatelier's principal) equilibrium shift towards the side with less moles of gas?
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Is the water in an aqueous solution undergoing a reaction considered part of the system or surroundings?
System: In chemistry, a system is a chemical reaction. A system operates within its surroundings. Energy can move between the two.
Surroundings: The environment around a particular chemical reaction....
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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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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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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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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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When is a reaction said to be under kinetic control, is it not easily reversible?
If we consider this reaction: Compound 1 + Compound 2 --> Compound 3
I understand that if a reaction is under kinetic control, the less stable (e.g. a mono-substituted diene) is formed and if the ...
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Would the change in enthalpy change of chemical reaction in space be considered as change in internel enrgy?
The formula of enthalpy change is
change in H = U + P*(change in V)
In space since there is no air, thus atmospheric pressure = 0 , P= 0 , Pv = 0 ,
So will H = U ?
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What is meant by work done "expanding against atmosphere"?
In the book, Chemistry : A molecular approach, I came across this line:
Over here what does the author mean by work done by expanding against atmosphere?
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Energy at constant Entropy and Volume
The system of constant entropy and constant volume will attain the equilibrium in a state of minimum energy. Why?
I know that:
$\Delta G= \Delta H-T\Delta S$
And at constant volume and entropy: $\...
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Is a person warmed by fire an example of endothermic reaction? [closed]
My chemistry textbook gives the example of a man being warmed by a fire as an endothermic reaction. If the man's body is the system and it is increasing in temperature, how can this be endothermic?
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Chemical potential of mixtures of ideal gases and the Gibbs-Duhem equation
As is well known for a constant composition system, $\mu$ (symbolizing chemical potential) is equal to the molar Gibbs energy. Using
$$
\mathrm{d}G = V\mathrm{d}p-S\mathrm{d}T,
$$
we can write
$$
\mu =...
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Variation of equilibrium constant
In an exothermic reaction, the value of equilibrium constant increases with the rise of temperature because,
$\Delta H < 0$ ( exothermic reactions)
$\Delta G = \Delta H - T\Delta S$
Now if $\...
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How does change in entropy influence the tendency of a reaction to occur? [duplicate]
I know that entropy is the measure of the randomness of particles within a system, but how would it affect the tendency of the reaction? Would it just increase or decrease the chance of the reaction ...
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510
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Final temperature after caustic dilution: Interpreting the graph
I found the below graph in the Occidental Handbook on Caustic.
I'm confused, what may be the parameter noted on the four curves? 80-100-120-140 F?
The final Temperature is on the y-axis & ...
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Bomb Calorimeter vs Cup Calorimeter
In the textbook,it is said that bomb calorimeter measures the constant volume heat ,while the cup calorimeter measure Constant pressure Heat.I was wondering, why cup calorimeter is considered constant ...
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661
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How the Nernst equation is applied for electrodeposition? [closed]
For using the Nernst equation
$$E = E_0 - \frac{RT}{nF}\ln\frac{[\ce{Red}]}{[\ce{Ox}]}$$
the concentrations of $\ce{Red}$ and $\ce{Ox}$ species are required. For the reaction
$$\ce{Cu+ + e- <=&...
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