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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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24 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)?
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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 ...
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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 $(P_{2},V_{2},T_{2}).$ ...
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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 ...
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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 ...
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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 ...
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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 ...
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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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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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2answers
2k views

Does ice melt faster when submerged in water?

Suppose you have a container with a drain at the bottom full of frozen H2O which you leave a room temperature to melt. Will the ice melt faster if you drain the water as it melts? I would expect that ...
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0answers
506 views

Entropy of Activation and Temperature Dependence

I am trying to understand the extrapolation of enthalpy $\Delta H^{\ddagger}$ and entropy of activation $\Delta S^{\ddagger}$ from the Eyring equation. It's typically cast as: $$\ln\left(\frac{k}{T}\...
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1answer
13k views

Calculating the Gibbs Free Energy of Mixing

This is a Physical Chemistry Question and comes from the Atkins Physical Chemistry book. The answers are given but I don't understand how to get to $-9.7~\mathrm{kJ}$ for the first part of the ...
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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?
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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 ...
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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)...
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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}} - ...
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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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2answers
1k views

Temperature Dependent Specific Heat of Nitrogen

Calculate the change in enthalpy as 1kg of nitrogen is heated from 1000K to 1500K, assuming the nitrogen is an ideal gas at a constant pressure. The tempreature dependent specific heat of nitrogen is ...
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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
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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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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 $\...
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2answers
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Chemical reaction that can produce lots of heat from 2-3 simple liquid ingredients?

Have an experiment I want to try out utilizing thermoelectric power and I want to generate the heat via a simple chemical reaction. Ideally I'd like to mix 2 liquids together (one being water or ...
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
703 views

Is there a relationship between viscosity and enthalpy of vaporization?

It would be useful to be able to predict relative evaporation rates of liquids. For small reduced temperatures the heat of vaporization is relatively constant, but it is not one of the more common ...
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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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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
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 ...
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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 ...
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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

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 &-&...
2
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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 ...
12
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1answer
1k views

How to make approximation of rotational partition function of diatomic linear molecules?

Using the rigid rotor approximation to the level energies, and such other appropriate assumptions, we can approximate rotational partition function, $Q_{\mathrm{rot}}$, of linear molecules as follows: ...
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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 ...
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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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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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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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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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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 ...
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1answer
1k views

Why doesn't my stainless steel Thermos get really really hot?

Why doesn't my stainless steel Thermos get really really hot? Seems like a fairly straightforward question. A few notes: I was looking and found (obviously different values because steel is an alloy)...
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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 $\...
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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
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^\...
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1answer
59 views

Can Substances on Titan be Reacted at a Thermodynamic Gain?

Titan, a moon of Saturn, has readily available water ice ($\ce{H2O}$) and methane ($\ce{CH4}$) on its surface, at a frigid $\pu{93.7 K}$. It would be significant if these (or possibly, other ...