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.
1,749
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0answers
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Numerical analysis of Hydrogen bond between F- and CH3COOH [on hold]
The hydrogen bond between $\mathrm{F^{-}}$ and $\mathrm{CH_{3}COOH}$ is very strong and is strength may be analysed by setting up a Born Haber cycle, with the following data (in $kJ/mol$):
Lattice ...
1
vote
1answer
49 views
How to find the Cp, difference of Cp and heat of fusion from the dependence of vapor pressure on temperature?
The vapor pressure of zinc varies with temperature as
$$\log P(\pu{mm Hg}) = -6850/T - 0.755\log T + 11.24 \label{eqn:1}\tag{1}$$
and that of liquid zinc as
$$\log P(\pu{mm Hg}) = -6620/...
1
vote
0answers
48 views
How to I find the equilibrium temperature in this problem?
From Castellan's Physical Chemistry, chapter 12 [1, p. 276]:
12.18 At $\pu{25 °C}$ we have for rhombic sulfur: $ΔG_\mathrm{f}^\circ = 0,$ $ΔS^\circ = \pu{31.88 ± 0.17 J K-1 mol-1};$ and for ...
1
vote
1answer
49 views
Constant Pressure and Temperature during Phase Change
One of the solution guides to a question I was working on said that pressure and temperature is constant for a phase change. I understand why temperature is always constant for a phase change, but don'...
2
votes
1answer
54 views
Application of Nernst Equation in Potentiometric titration of Fe2+ with Ce4+
It is well Known that to find $E_{cell}$ during titration of $Fe^{2+}$ with $Ce^{4+}$ we consider 3 domains:
Before Equivalance point , $E_+ = E_{Fe^{3+}/Fe^{2+}}^o+\frac{RT}{nF}log\frac{[Fe^{3+}]}{...
-4
votes
0answers
18 views
Show that the following processes are irreversible [closed]
Show that the following processes are irreversible. (a) Gas freely expands from V to V+dV (dV>0) adiabatically, and (b) Gas expands adiabatically from p to p+dp (dp<0) via the Joule-Thompson ...
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0answers
32 views
What is the ΔG* value for nucleation? [closed]
To be honest, I would like to know how $\Delta G^*$ is different from $\Delta G$ in general and whether the star has any other significance.
Now, moving to the second question. I was asked to find $\...
0
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0answers
27 views
Software to predict equilibrium products in the ideal gas phase
I'm interested in software packages that can answer the following kind of question:
If I mix 30mol% $N_2$ and 70mol% $H_2$ together at 2 bar and 2000C, what is the equilibrium composition after all ...
-1
votes
0answers
47 views
Chemical Equilibrium problem
I can't seem to get the answer that appears on the back of the book
Here is what i did:
a)
$K_p=K_x p^{\Delta N}$; in this reaction $\Delta N =-1$, then $K_pp=K_x$
from $\Delta G=-RT\log K_p$ I ...
-1
votes
1answer
43 views
Boiling point elevation does not depend on the solute? [closed]
I've recently carried out an experiment trying to measure the boiling point elevation of water after adding 5M of NaCl and KCl. Although for some reason, KCl solution started boiling around 90 degree ...
2
votes
2answers
81 views
Temperature measurement
Consider some liquid in a beaker. I am measuring its temperature using a thermometer. When i put my thermometer's bulb in the liquid, the particles of the bulb gain the same kinetic energy as of the ...
1
vote
2answers
30 views
Spontaneity of an exothermic chemical reaction
When the process is exothermic (ΔHsystem<0), and the entropy of the system increases (ΔSsystem>0), the sign of ΔGsystem is negative at all temperatures. Thus, the process is always spontaneous.
...
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0answers
34 views
Calculating heat of neutralisation
Two acids $\ce{HX}$ and $\ce{HY}$ have strength ratio $5:2$. Their heat of neutralisation are in ratio $5:4$. If $40\ \mathrm g$ of $\ce{NaOH}$ is added to a mixture of acids containing $1\ \mathrm g$ ...
1
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4answers
72 views
Basic concept of the first rule of thermodynamics
There is a cylinder-piston system with some gas in it, and let's say this system is a closed system.
Say that the system is submerged in a large beaker of water whose temperature is $25\ \mathrm{^\...
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1answer
27 views
What is the the total heat extracted in the process? [closed]
Since this is a cyclic process:- Change in internal energy=0.
In the process C-A the work done W is zero, thus the heat Q is zero since it is an isochoric process.
Next in the process A-B, I got the ...
0
votes
2answers
47 views
Temperature measurement using thermometer [closed]
I have two samples of water – 'A' and 'B'. My thermometer measured them to be 90 °C. They both have different volumes. So, the kinetic energy of the particles of sample A and B is same or different? ...
1
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0answers
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What is the degree of freedom of the calcium carbonate dissociation reaction?
Question
$\ce{CaCO3}$ dissociated in a closed system according to the reaction:
$$\ce{CaCO3(s) -> CaO(s) + CO2(g)}$$
Assuming the reaction is in thermodynamic equilibrium, what is/are ...
1
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0answers
35 views
Identifying endothermic and exothermic reaction [closed]
How can I know that a given reaction is endothermic or exothermic? I know that all combustion reactions are exothermic. But what about other reactions?
In my school exam I was asked about whether the ...
0
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3answers
1k views
Are all volatile liquids combustible?
I realized that liquids like petrol, kerosene and even perfumes are combustible when they are volatile.
Could that be the reason why water is not combustible is because it is not volatile?
Are ...
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0answers
42 views
Calculating thermodynamic quantities for hydrogenation of iron nitride
HW#6.3 If the reaction
$$\ce{Fe2N(s) + 3/2 H2(g) <=> 2 Fe(s) + NH3(g)}$$
comes to an equilibrium at a total pressure of $\pu{1 bar},$ analysis of the gas shows that at $\pu{700 K}$ ...
2
votes
0answers
76 views
Why can't calorimetry be used to measure fast reactions?
As my previous post was a bit unclear and unspecific, I am reformulating it. First of all this is a question that I had while reading some concepts my book introduces, so this isn't a homework ...
1
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2answers
69 views
How to calculate the standard Gibbs free energy of formation of bromine vapor at room temperature?
The normal boiling point of liquid bromine is $\pu{58.2 ^\circ C}$. At $\pu{9.3 ^\circ C}$ the equilibrium vapor pressure of liquid bromine is $\pu{100 torr}$.
From this data, calculate the standard ...
0
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1answer
44 views
Entropy changes during transfer of heat between two bodies
Consider two metal blocks, one at 500K and another at 300K, they are bought to contact with each other until they reach a common temperature.
Find the entropy change of each object and the total ...
3
votes
1answer
196 views
Relation between First Law of Thermodynamics and Ideal Gas Law
Thermodynamics has always been a tough thing for me. There are lots of assumptions in this subject (those assumptions, I know, are necessary, I know the science of thermodynamics is a very practical ...
0
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0answers
24 views
Reaction between chlorine gas and oxygen at 600 degrees Centigrade
Chlorine gas will not normally react with oxygen gas directly at STP. However, would the two react at standard pressure and 600 degrees Centigrade?
3
votes
1answer
67 views
Thermodynamic vs kinetic basicity [closed]
I'm writing something related to basicity and came across few papers that distinguish thermodynamic and kinetic basicity.
"In particular, the study of hydrogen bonding (H-bonding) within proton ...
0
votes
1answer
44 views
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 ...
0
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1answer
61 views
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})$$
However, for $\Delta H(\text{solution})$ to be exothermic, it has to have a negative value ...
1
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1answer
30 views
Boiling point elevation and liquid solutions
$\pu{1 L}$ of an aqueous solution of urea having density $\pu{1.06 g mL-1}$ is found to have elevation in boiling point $\Delta T_\mathrm{b} = \pu{0.5 °C}.$ If the temperature of this solution is ...
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0answers
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Computing enthalpy of formation of dissolved gas from its enthalpy of dissolution
Provided that I know the enthalpy of formation $\Delta H_f^0(X_{g})$ of a substance $X$ in gas phase and its enthalpy of dissolution $\Delta H^0_{sol}(X)$ in the same conditions, considering that the ...
1
vote
2answers
80 views
How to derive this temperature-pressure-specific volume relationship?
(for isentropic, adiabatic, ideal gas flow)
$$\frac{T_x}{T_y} = \left(\frac{p_x}{p_y}\right)^{\frac{(\gamma-1)}{\gamma}} = \left(\frac{V_y}{V_x}\right)^{\gamma-1}$$ where $V$ is the specific volume, $...
1
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1answer
123 views
Finding the isotherm with given minima
Get the temperature of the isotherm for water for which the local minimum is at $\pu{100 Pa}.$ Use the values of $a$ and $b$ of water.
My approach
In the van der Waals equation, set
$$\frac{\...
2
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0answers
27 views
What is total enthalpy?
I've seen that it's defined as $h_0 = h + \frac{v^2}{2}$, where $h_0$ is the total enthalpy per unit mass. I can see that the $\frac{v^2}{2}$ term probably has something to do with kinetic energy, but ...
5
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1answer
244 views
Is the equation dG = Vdp − SdT valid only for a reversible process? Can it be applied for an irreversible one too?
In the derivation, we write:
$$
\begin{align}
G &= H - TS &\quad&\to&\quad \mathrm dG &= \mathrm dH - T\,\mathrm dS - S\,\mathrm dT \\
H &= U + pV &\quad&\to&\quad ...
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votes
1answer
37 views
Why aerosol forms when you take a hot shower in a very cold day? [closed]
When temperature is about $\pu{17 ^\circ C}$ and I open the hot shower in maximum temperature (for a common electric shower) the air gets almost immediately full of droplets and this lasts the entire ...
1
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1answer
46 views
What is the meaning of the phase state label (cr,l) appearing in ATcT thermochemical data tables?
I was examining data associated with this post on the heat of solution of ammonium nitrate when I came upon the NIST ATcT data page which lists the heat of formation of $\ce{(NH4)NO3(cr,l)}$. In this ...
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3answers
47 views
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 ...
0
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1answer
30 views
Applying Raoult's Law in volatile solids–liquid solutions
My textbook explains applying Raoult's Law for the two cases:
liquid–liquid solutions, in which the vapour pressure of the solution is due to both the components
non-volatile solids–liquid solutions, ...
0
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0answers
29 views
How do you find the heat capacity ratio of combustion products?
For example, if gaseous oxygen $(O_2)$ and paraffin wax $(C_{32}H_{66})$ were to stoichiometrically combust at STP, how would one go about finding the heat capacity ratio ($\gamma={c_p \over c_v}$) of ...
0
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2answers
61 views
Coffee cup lids
So this morning I purchased a coffee. As a not uncommon event the lid on the coffee cup didn't have a hole completely punched through (a gas inflow hole). This makes it difficult to drink the coffee ...
9
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1answer
502 views
The heat content of the products is more than that of the reactant in an … reaction
The heat content of the products is more than that of the reactant in an ............. reaction.
In this question the answer given is "exothermic"; yet I thought the answer would be endothermic as ...
0
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1answer
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How can I calculate the equilibrium constant for this reaction?
Silver(II) oxide partially decomposes into solid silver and oxygen gas according to:
$$\ce{2 AgO(s) <=> 4 Ag(s) + O2(g)}$$
with enthalpy $H^\circ = \pu{62.0 kJ}$ and entropy $S^\circ = ...
-1
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1answer
42 views
What's greater, enthalpy of combustion or heat of combustion? [closed]
What is the difference between the two? In my assignment book there is this question which asks if enthalpy of combustion is greater than, equal to or less than the heat of combustion. The answer ...
3
votes
1answer
59 views
Relationship between Gibbs free energy and potential energy (related to reaction coordinate diagrams)
For a rate law, the rate constant $k$ is given by the equation
$$\ln k = \ln A - \frac{E_\mathrm{a}}{RT}\tag{1}$$
If $k_\mathrm{fwd}$ is the forward rate constant and $k_\mathrm{rev}$ is the reverse ...
3
votes
1answer
42 views
Facing a problem in enthalpy calculation
If 1 mole of gaseous carbon atoms are converted into diamonds, calculate enthalpy change of process given that bond enthalpy of $\ce{C-C}$ bond is $\pu{400 kJ mol-1}.$
According to me, the answer ...
0
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0answers
25 views
Thermodynamics of Acid Base Neutralisation
I was attempting an exam in which they questioned us about the thermodynamics of acid-base reaction.
The question was this:
In neutralisation reaction of a strong acid and a strong base in a ...
0
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0answers
40 views
Diffusion between phases based on chemical potential
How is the concept of diagram(b) different from that of (e) and (d) from (f)?Someone told me in one of my earlier posts (Why will A atoms diffuse from β phase to α phase and B atoms from α phase to β ...
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0answers
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Enthalpy of formation at other temperatures
I was told each compound has an enthalpy of formation of 0 at the standard temperature if it is in it's lowest energy modification. But what if we change the temperature? It would make sense to me ...
2
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0answers
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Why will A atoms diffuse from β phase to α phase and B atoms from α phase to β phase?
At the initial compositions 1 and 2 of $α$ and $β$ respectively the chemical potentials of A and B atoms in each phase can be found by extrapolation of the tangents to the free energy curves at 1 and ...
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1answer
31 views
Why does a system want to achieve randomness to be feasible? [closed]
According to entropy and gibbs free energy, randomness is one of the factors that determines reaction spontaneity, but why? Shouldn't it be the opposite?
