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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1answer
25 views
Quasi-static implies that T aprox equals Tsurr?
A few days ago I re-visited my undergraduate thermodynamics notes and (as you may have seen from the amount of questions I have been posting) I have encountered many difficulties that I overlooked at ...
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1answer
23 views
thermodynamics of solid-liquid of acetic acid and glycerol [on hold]
Can glycerol (and acetic acid) change from solid to liquid when compressed at room temperature (20 degrees celsius)?
1
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1answer
69 views
Work done in an irreversible process
I was given a problem to identify whether the given statement is true or false.
And the statement was:
"Consider an ideal gas which is expanded from $(P_{1},V_{1},T_{1})$ to $(P_{2},V_{2},T_{2}).$ ...
1
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1answer
73 views
Determine surface area of heat exchange tube
A heat exchanger is used to cool down a stream of $\pu{20 kg s-1}$ of water from $\pu{80 °C}$ to $\pu{60 °C}$. The cooling water enters at a rate of $\pu{12 kg s-1}$ and $\ce{20 °C}$. The overall heat ...
1
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1answer
36 views
When a piston cylinder system that evolves isothermally and quasistatically is irreversible?
Suppose we have two states: $\ce{A}$ and $\ce{B}$.
Considering a quasi-static isothermal process of an ideal gas, (and another condition, that is $T = T_\mathrm{surr}$) that join those states.
Then ...
3
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1answer
34 views
Equation for overall heat transfer coefficient
The heat flow (in $[\pu{J/s}]$) through the wall of a tube of length $L$ and inner radius $R_0$ is
$$Q = (2πR_0L)U(T_{1\infty} - T_{2\infty}),$$
where $T_{1\infty}$ is the bulk temperature ...
2
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0answers
38 views
Existence of single ion activities
I have used Davies equation to find what I believed was single ion activities and multiplied them on concentrations to define the thermodynamic dissociation constants for any kind of buffer to find ...
2
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1answer
48 views
Freezing trend of water
In this experiment, I used a digital temperature probe to measure the freezing point of water and some other salt solutions.
I was just wondering if there was any explanations for 1. The first ...
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2answers
64 views
Concept of enthalpy at a given temperature
In thermodynamics, we always quote a fixed temperature, whenever we mention enthalpy of a reaction. For instance, one can determine the enthalpy of combustion of methane at 25 °C. Now almost all ...
5
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1answer
259 views
Need some help proving the following statements in Thermodyamics?
So in my second year thermodynamics class we are currently talking about entropy and deriving its definition from the 1st law.
$$\mathrm{d}q_{rev} = dU - dw_{rev}$$
$$= C_{V}(T)dT + PdV$$
$$= C_{V}(T)...
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1answer
60 views
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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0answers
29 views
Melting lithium carbonate [on hold]
I need to melt lithium carbonate and hold it between its melting point and 750 °C. Based on research so far, I think making an electrical DC-powered heater with a nichrome heating element would be ...
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0answers
9 views
Molecular formula and structure of Alkanes [closed]
Draw the structure for the following Alkanes and state the molecular formula for each
No.1
5-propyl-3methyloctane
No.2
3-ethyl-4methlyheptane
No.3
2,2-dimethylpropane
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0answers
17 views
Thermodynamics in a bottle of water [closed]
Can I boil a bottle of water just by shaking it and increasing its internal energy given that the wall that seperates water from surroundings is an adiabatic wall?
1
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1answer
39 views
Will the motion of particles always increase with the rise of temperature?
I came across this following question while poring over my textbook.
Predict the change in the motion of particles you would expect in the following if the temperature was increased:
a) Solid
b)...
1
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1answer
32 views
I am looking for any substance that would be unstable or dangerous when it is cooler or not on heat, and is stable when it is being boiled
I am a first responder and one of our protocols when entering any unknown lab environment is to turn off any burners. Most of the time, we try to not disturb the environment as much as possible so a ...
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0answers
23 views
Enthalpy of formation of Sodium oleat [closed]
I have a soap project and wish to do engineering calculation , I need to calculate the heat required to transform olein into soaps I need the value of the enthalpy of formation of sodium oleate.
I am ...
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0answers
13 views
Percentage Dissociation of N2O4 [closed]
When heated to 100 Degree Celcius and at pressure of 720mmHg , 17.2 gram of N2O4 gas occupy a volume of 11.450 cc.
Assuming that the ideal gas law applies , calculate the percentage of dissociation of ...
2
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2answers
68 views
Hydrogen vs neon in terms of entropy
I know that both molecular size and complexity increase overall entropy, but between the two I'm not sure which increases it more. Would 1 mole of hydrogen have the greater entropy because it is two ...
0
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0answers
54 views
Freezing point depression of salt solutions
I have recently come across this particular equation which is used to estimate the freezing point depression of a salt solution:
$$\theta_\mathrm{B} = \frac{\Delta H^\mathrm{fus}_{0,T_\mathrm{F}} - ...
2
votes
1answer
59 views
Free energy of solvation and Henry's law constant
I am trying to calculate the free energy of solvation of $\ce{CO2}$ from its Henry's law constant. As given on Wikipedia, the dimensionless Henry's law constant is $0.83$. If I try to calculate $\...
2
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1answer
68 views
How are octet-rule models supported by thermodynamics and quantum theory? [closed]
I understand that the four quantum numbers dictate how many electrons can "fit in a shell," but I don't understand how gaining a full octet is particularly energetically favorable.
The example of ...
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1answer
30 views
Thermodynamics at absolute temperature [closed]
Assume I have kept a single molecule in vacuum and in absolute zero (0 K) temperature. There is no energy left in the particle, and hence any type of motion is absent.
Now, what happens when I ...
0
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1answer
41 views
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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1answer
543 views
Why was a Plimsoll symbol chosen to indicate standard state?
Historically, the Plimsoll symbol (aka Plimsoll line) was created as hull mark that would serve as a ready indicator of whether a ship was overloaded and thus running too low in the water. It was ...
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1answer
30 views
Whats the difference between reversible process in thermodynamics and reversible chemical reactions?
We know that in thermodynamics, reversible process never occur since entropy should be conserved. However, in chemistry we do have a lot of reversed chemical reactions that forms reactants from ...
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4answers
50 views
Is the titration of sodium carbonate with hydrochloric acid temperature dependent?
I am a chemistry teacher in a Cambridge school.
In one of the titrations of sodium carbonate with HCl, there was one question asked:
On heating the sodium carbonate solution before doing the ...
0
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1answer
29 views
Impact of Pressure on equilibrium of Tin allotropes
The pressure at the bottom of the Mariana Trench in the Pacific Ocean is $1090$ bar. What temperature will the two allotropes of tin be at equilibrium? Assume that the molar volume, energy, and ...
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1answer
68 views
What is the molar enthalpy of reaction
When 0.45 g of Zn is added to 50.0 ml of 0.95 M HCl solution, the solution inside the calorimeter heats up by 12 °C. What is the molar enthalpy of the reaction (in kJ/mol)?
I know how to find the ...
2
votes
1answer
62 views
Calculating ΔH from bomb calorimetry
Suppose we carry out a reaction in a bomb calorimeter whose starting temperature is $298.15\ \mathrm K$. Here we assume $\Delta V$ is close enough to zero that we consider the process to be at ...
0
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1answer
30 views
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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4answers
45 views
Adiabatic processes and the Ideal Gas Law [closed]
in my first year chemistry textbook it wrights that in adiabatic proccess when there is a system of canister filled with gas and a piston above(and wheights on it) if we let the piston move upward by ...
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3answers
46 views
Is it correct to say that “some degree of pollution is an inescapable consequence of the Second Law of Thermodynamics”?
The quote above is from ‘Enlightenment Now’ by Steven Pinker, I was just wondering if this was true or if it misrepresented the Second Law.
The full quote below...
...some degree of pollution is ...
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0answers
19 views
Is the electrode potential the first reading you get from a voltmeter?
I am using a digital voltmeter to measure the electrode potential of a Daniell cell, and I was told that the electrode potential was the first reading... but it kind of fluctuates initially... I don’t ...
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2answers
70 views
dSsur, dS and dStotal relation
By definition,
dS=dqrev/T.
Based on my understanding, the subscript rev means that the dq is heat exchanged in a reversible pathway from a state i to another state f, regardless of the actual ...
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2answers
50 views
Does dissolving something in water change the specific heat of the solution?
I’m a little confused on this topic. If I have a solid that I dissolve in water and that undergoes an exothermic reaction, can I assume that the specific heat $c$ of the solution instantaneously after ...
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0answers
33 views
Calculating the amount of a product at the reaction equilibrium
$\ce{Cr2O3}$ can be reduced to the elements chromium with high temperature and carbon by this two reactions:
$$
\begin{align}
\ce{Cr2O3(s) + 3C(s) &-> 2Cr(s) + 3 CO(g)} \label{rxn:1}\tag{1}\\
\...
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1answer
25 views
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 $\...
1
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1answer
69 views
Calculating temperature change of helium due to Joule-Thomson effect
We are trying to fill a rocket helium tank that is 78 liters with helium, final pressure of $\pu{10500 psi}$. We plan to pressurize high pressure tanks to $\pu{20000 psi}$ using a compressing pump ...
2
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0answers
41 views
What is Delta H for dissolution? [closed]
An ionic compound has a solubility of $1\ \mathrm M$ in water at $25\ ^\circ \mathrm C$ and its solubility increases as the temperature is raised. What are the signs of $\Delta H^\circ$ and $\Delta S^\...
2
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1answer
46 views
Reaction energy of oxygen and hydrogen
From the bonding energy of following bonds that I found in a Wikipedia article, I calculated the reaction energy that would be released when oxygen and hydrogen are reacted to produce water. The phase ...
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0answers
24 views
Heat capacity from limited information
I am trying to figure out how an author has determined the heat capacity of a substance from limited information. The authors cite a particular book that contains only the following information:
$H_{...
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1answer
25 views
How is “the surrounding” and its temperature defined to calculate entropy change during a reaction?
Lets say supercooled liquid water at $263\ \mathrm K$ isobarically changes to solid ice at the same temperature. I wish to calculate the change in entropy of the surroundings and I happen to know the $...
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0answers
22 views
Deriving the entropy as a function of concentration
In a physical chemistry class, the professor derived entropy $S$ as a function of concentration starting from $S=k\ln(W)$. Somehow he made a mistake and ended up with the wrong sign. This remains ...
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2answers
53 views
Why enthalpy is defined at a constant pressure?
How absolute enthalpy and enthalpy change are defined? What is the clear difference between enthalpy and heat? Is it the constancy of pressure what makes the enthalpy a state function?
My teacher ...
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1answer
45 views
adiabatic expansion vs Joule-Thomson Effect
Source: The1stLawofThermodynamicsLesson4
I am looking for difference between adiabatic expansion and Joule-Thomson effect. Looking at the setup demonstrating Joule-Thomson effect, I find no essential ...
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0answers
34 views
Safe liquid with a boiling point > 275F
Is there a non toxic inexpensive liquid which can be safely heated to 275F without worry of it combusting? It would be used to apply heat to PVC to soften it for forming. Perhaps propolyne glycol?
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0answers
23 views
What drives the formation of salts?
Can someone explain why potassium and chlorine undergo an exothermic reactiom to form an ionic solid despite that potassium has an ionisation energy of 425 kJ mol-1 and chlorine has an electron ...
0
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2answers
59 views
Flow rate of the fuel consisting of ethanol and water burning in air of a given flow rate
I hope that someone could give me some hints or tips on how to approach this question, even though these types of questions are usually closed off as homework.
A burner is run by a fuel mixture of $...
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0answers
34 views
Is it possible to convert a combustion reaction directly into an electrochemical one?
I'm fairly inexperienced in chemistry so forgive me if this question is silly but, why is it not possible to convert a combustion reaction to an electrochemical one directly and harvest the electrical ...
