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.
2,225
questions
0
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1answer
8 views
Does temperature change if change in internal energy is zero?
I needed to find ΔU for the combustion of methane in a sealed rigid adiabatic container.
In the solution given : as q = 0 ; w = 0 ,So ΔU = 0 (by FLOT).
First Doubt:- that heat is released during ...
0
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0answers
12 views
Effect of specific heat capacity on heat loss
Assume we want to calculate the heat capacities of two substances with different heat capacity. We heat them both up with a immersion heater delivering a constant rate of energy (constant J/sec), and ...
3
votes
0answers
19 views
Calculating temperature of partial condenser, flash calculations
The iterative method I have learned to make flash calculations for a binary system where I know the inlet feed (F [mol/s]), total composition of the two components ($z_1$ and $z_2$), the amount of the ...
0
votes
0answers
11 views
How to calculate the unknown concentration with delta H and delta S? [closed]
3-ethyl-4-methylhexa-1,3-diene undergoes a combustion reaction. For this reaction, the following
concentrations were used: [O2] = 0.06 M, [CO2] = 0.09 M and [H2O] = 0.10 M. Determine the
concentration ...
3
votes
2answers
32 views
Isobaric entropy relation from isothermal Gibbs free energy relation
I have been given a problem to derive a relation for change in entropy from change in Gibbs free energy:
Starting with the isothermal equation
$$G(p_2) = G(p_1) + nRT\ln\frac{p_2}{p_1}\label{eqn:1}\...
2
votes
1answer
82 views
How is Gibbs free energy related to stability?
I have been learning thermodynamics for quite some time and I fail to relate Gibbs free energy and stability.
For example, how do I compare stability of metal oxides using the following data?
Also, do ...
0
votes
0answers
34 views
Is it possible to solve for the equilibrium value given only the initial amounts of reactants? [closed]
At $\pu{90 °C}$ following equilibrium is established:
$$\ce{H2(g) + S(s) <=> H2S(g)}$$
If $\pu{0.20 mol}$ of hydrogen and $\pu{0.1 mol}$ of sulfur are heated to $\pu{90 °C}$ in a $\pu{1.0 L}$ ...
-1
votes
0answers
47 views
What is the effect on Kp on doubling the volume?
Following reaction takes place at $\pu{127 ^\circ C}$ and $\pu{5 L}$ vessel,
$$\ce{SO2Cl2(g) <=> SO2(g) + Cl2(g)} \qquad K_p = \pu{1 atm}$$
(a) If initially only $\ce{SO2Cl2(g)}$ was present at $...
0
votes
0answers
21 views
Standard heat of reaction [closed]
Nitrous acid ($\ce{HNO2}$) is used to solidify olive oil for shipping or for making margarine. It is
highly unstable. What is the standard heat of reaction, or $\ce{ΔH}$, in $\pu{kJ/mole}$, for the
...
-1
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0answers
25 views
How much energy is transferred [closed]
Aluminum has a specific heat capacity of $\pu{0.90 J g-1 ^\circ C-1}$ and water has a specific heat capacity of
$\pu{4.184 J g-1 ^\circ C-1}$. How much energy is transferred from a piece of hot ...
-1
votes
1answer
27 views
Derivation of Enthalpy Equation
Why are they taking delta H in equation (iv) to be at constant pressure while in the same equation they are considering delta E to be at constant volume to arrive at equation (v)? If they are arriving ...
1
vote
1answer
31 views
Can endergonic reactions be driven by heat?
I am having trouble conceptualizing endergonic reactions and their difference from endothermic reactions. An endergonic reaction is one that has a positive Gibbs free energy change, such that energy ...
-2
votes
2answers
35 views
what is the change in enthalpy during constant volume
I have been studying thermodynamics for quite a time now, and recently learned about enthalpy
but I have been facing a lot of problems
So,which is the correct equation of enthalpy
$$\Delta H=\Delta U+\...
-1
votes
0answers
22 views
How to learn the concept behind Thermodynamics, Equilibrium, Electrochemistry, Chemical Kinetics [closed]
I am currently reading Thermodynamics, Chemical Equilibrium, Ionic Equilibrium, Electrochemistry, Chemical Kinetics for JEE Advanced exam in India. Now when I am solving problems I can not inter ...
0
votes
0answers
25 views
Why do we use nCv∆T=∆U almost universally(for ideal gases)
In my understanding $C_V$ which is defined when the volume is constant is written as
$$C_V=\frac{q_V}{\Delta T}$$
Thus,
$$q_V={nC_V\,\Delta T}$$
since for an isochoric process work done is zero
$$\...
1
vote
2answers
107 views
What is the definition of thermodynamic stability?
The term thermodynamic stability is used on this site, but I can't find a good definition. Is is a quantitative or a qualitative concept? Does it apply to a single compound, or a pair of compounds? ...
0
votes
1answer
46 views
Equilibrium for the synthesis of methanol
Liquid methanol is obtained with carbon monoxide gas and hydrogen gas in a reactor at $\pu{300 °C}$ and $\pu{250 atm}.$ $K_p = \pu{9.28E-3}.$ Find $K_c.$
With only these data, do I have to use the ...
-1
votes
0answers
11 views
Quasi Static Process and Reversibility of Engines
So I understand that In a quasi static process, the temperature of the system is changed ever so slightly and slowly until it reaches its final temperature,so that at each stage of temperature change, ...
2
votes
0answers
67 views
Why is U the symbol for lattice energy?
I often see $U$ or even $\Delta U$ being the symbol for lattice energy. Why is that? Does it refer to internal energy?
1
vote
1answer
122 views
Choice of lower bound of curve for PV work
I am told that the area under the PV curve gives the magnitude of work done by a gas.
Let $V_i$ be the initial volume, $V_f$ be the final volume, and the pressure as a function of volume be given by $...
1
vote
0answers
33 views
Entropy of free expansion and isothermal process
Let me tell what I understand of the concepts on which the question is based first.
Heat is a flow of energy that takes place due to a temperature gradient.
When doing reversible isothermal expansion ...
0
votes
1answer
86 views
Total entropy change for a spontaneous reaction
For the oxidation of iron,
$$\ce{4 Fe(s) + 3 H2O(g) -> 2 Fe2O3(s) + 3 H2(g)}$$
the entropy change is $ \pu{–549.4 J K^{-1} mol^{-1}}$ at $\pu{298 K}.$ In spite of the negative entropy change of ...
3
votes
2answers
52 views
How can change in entropy be the same for all processes if the entropy production $\sigma$ is present for irreversible processes?
From the definition of entropy change,
$$S_2-S_1=\left ( \int_{1}^{2} \frac{\delta Q}{T}\right )_{int.rev}$$
From the closed system entropy balance, we have
$$S_2-S_1=\left ( \int_{1}^{2} \frac{\delta ...
1
vote
1answer
47 views
Compound with pressure sensitive melting point at moderate temperature and pressure
I'm in need for a compound with ideally all of the following properties:
A melting point of 5 °C or less at 1 atmosphere (or slightly lower pressure)
A melting point of 12 °C or more at less than 20 ...
0
votes
0answers
26 views
Why does chemisorption decrease with increasing temperatures?
Why is it that chemisorption decreases with higher temperatures?
The explanations I found online were quite vague and one of them cited Le Chatelier's principle, but I thought chemisorption is an ...
1
vote
2answers
63 views
Is it valid to calculate concentrations given equilibrium constant and initial concentration?
Suppose we have the following reaction:
$$\ce{2A <=> B + C}\tag{1}$$
which can be thought the sum of the following reactions:
$$\ce{A <=> B}\tag{2}$$
$$\ce{A <=> C}\tag{3}$$
with ...
-1
votes
3answers
67 views
What is non toxic to fish, has a low freezing point, and floats on water?
I am looking for a liquid that floats on water that will prevent the water from freezing (or at least slow it down). The application would be a small area (less than a square foot). It has to be non-...
2
votes
0answers
13 views
Is standard change in activation Gibbs free energy indepedent of pressure?
For a chemical reaction the activation volume is defined as:
$$Δ^{\ddagger}V={V^\ddagger}-V$$
where both $V^\ddagger$ and $V$ refer to standard states (I have omitted the symbol for simplicity). One ...
2
votes
1answer
350 views
Can someone clear this confusion I have about the first law of thermodynamics
In our school we were taught that the first law of thermodynamics represented mathematically is $\Delta U=Q+W$. Also we were taught that for an isothermal process $\Delta U=0$ and therefore $Q=-W$, ...
1
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0answers
25 views
Are all exergonic reactions spontaneous?
Exergonic reactions have a negative $\Delta G$: the system loses free energy. Spontaneous reactions are also defined in the same way, as far as I know. Does this mean the two are synonymous?
There are ...
-1
votes
0answers
18 views
adiabatic reversible process problem
A compressor recieved air at To= 300 K and at pressure Po= 1 atm. At the exit, P1 = 2 atm. The process inside the compressor is (A) adiabatic and reversible (B) gas is an ideal gas (3) gamma = Cp/Cv = ...
0
votes
1answer
74 views
What is the general phenomenon taking place here?
For many cases while calculating the activity of a particular species I find them calculating like this:
$$a=\frac{p_{Mn}}{p^{\circ}_{Mn}}$$
What I really do not understand is what is evaporating into ...
6
votes
3answers
863 views
Why is the sum of two inexact differentials exact?
From the first law of thermodynamics, $\mathrm{d}U = đQ + đW$, where $\mathrm{d}$ represents an exact differential and $đ$ an inexact differential. Exact differentials correspond to state functions ...
-1
votes
0answers
26 views
Relation between Entropy, Resonance and stability
Why is it so that the continuous Delocalisation of electrons in a molecule tends to lower the total internal energy of the molecule? I understand that there is a distribution of energy in multiple ...
0
votes
1answer
48 views
Confusion between various formulas of Gibbs free energy [closed]
According to the assumptions of Constant P and T and no non mechanical work, we get
ΔG=ΔH-TΔS
But there is another form of the Gibbs free energy equation which takes Reversible process and no non ...
-1
votes
0answers
34 views
Elementary derivation relating Gibbs energy with equilibrium constant
Is there an elementary derivation of $\Delta G = \Delta G° + RT \ln K$ where pressure and temperature are assumed to be constant (typical biological conditions; particularly for aqueous reactions)?
I ...
0
votes
1answer
92 views
Can G, H, and S be negative?
Consider Gibb's free energy of a reaction in a closed system $G = H - TS$. Can $G$ ever be negative? (note, I am not talking about $\Delta G$)
I would suspect no because there is always some energy ...
1
vote
1answer
149 views
Can vapour pressure be used to 'generate' work for free?
Given a bottle of water, a closed system, some of the water molecules in the liquid phase will have enough energy to escape that phase, forming water vapour, contributing to vapour pressure.
Now ...
0
votes
1answer
54 views
Does the enthalpy of formation include translational and rotational energy?
I can look up the enthalpy of formation of water vapor and get -241,826 KJ/mol. I want to use this to compute the total energy of water vapor at STP from the energies of O2 and H2 gas. What I don't ...
1
vote
1answer
52 views
New relationship between exponential factors and entropy of a reaction?
Consider the reaction $\ce{A <=> B}$. Let $k_f$, $E_A$, and $A$ denote the forwards rate constant, activation energy, and pre exponential factor, respectively. Let $k_r$, $E_A'$, and $A'$ denote ...
-1
votes
1answer
41 views
Why is the standard enthalpy of formation of aluminium oxide higher than magnesium oxide?
$$\begin{align}
&\text{Aluminium oxide:} &\ce{4Al + 3O_2 &-> 2Al2O3} &(\Delta H_\mathrm f &= \pu{-1675 kJ/mol})\\[1.5em]
&\text{Magnesium oxide:} &\ce{2Mg + O_2 &-&...
-2
votes
1answer
47 views
Le Chateliers principle and increase in temperature [duplicate]
If you increase the temperature, the endothermic reaction is favored. The Le Chatelier's principle states that the endothermic reaction is favored in order to minimize the effect of an increase in ...
-1
votes
0answers
36 views
Do external actions affect critical temperature?
Critical temperature $T_\mathrm{c}$ is the temperature when properties of both gas and liquid converge to the same values and the difference between the phases disappear:
$$T_\mathrm{c} = \frac{8a}{...
2
votes
1answer
61 views
Change in enthalpy and entropy when sugar dissolves in water
We know that dissolution of sugar in water is a spontaneous process.
So, change in Gibbs free energy $(ΔG)$ must be negative for the overall process:
$$ΔG = ΔH - TΔS < 0$$
Hence either the enthalpy ...
-1
votes
0answers
52 views
Enthalpy of Neutralisation for HF and strong base
Now I know that when a strong acid and strong base neutralise each other, enthalpy change is almost constant and equal to -57.3 kJ/mol. (This is because no heat is required to ionise the acid and base ...
-2
votes
1answer
89 views
Any examples of reactions where simpler molecules are combined into more complex ones and are endothermic at the same time? [closed]
Can you name examples of reactions that are endothermic and simple molecules are combined into more complex ones at the same time? Like what plants do they take heat and sunlight and they synthetize ...
0
votes
0answers
36 views
Why does a wooden spoon creates bubbles when put in hot oil?
This question might be a bit weird, but I just asked myself why a wooden cooking spoon creates bubbles when put in oil at about 170°C. This is a common trick to find out, if Oil has the right ...
2
votes
3answers
485 views
What does heterogeneous mean?
We say that a homogeneous sample consists of the chemically same type of molecules whereas heterogeneous ones vary chemically, i.e. the molecules throughout are not same and also not uniform.
Why do ...
3
votes
2answers
78 views
Ellingham Diagram for carbon [closed]
Consider the following reactions:
$$\begin{align}\ce{C + O2&->CO2}\tag{1}\\[1em]
\ce{2C + O2&->2CO}\tag{2}\\[1em]
\ce{2CO + O2&->2CO2}\tag{3}\\[1.5em]
[(2)+(3)]/2 &= (1)\end{...
1
vote
3answers
61 views
Specific Heats for Non-Constant Processes
Why can the specific heat at constant Pressure ($C_p$) be used to calculate the change in enthalpy as $\text{d}H = C_p\text{d}T\newcommand{\d}{\text{d}}$ for processes that are not even at constant ...
