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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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Thermodynamic Cycle

What is the value for $\Delta_f G^0(\ce{Cl^-}, \ce{aq})$ in this thermodynamic cylce: Do you agree it should be (with the formation free energy of $\ce{H^+} = 0$) $$-\Delta_f G^0(\ce{Cl^-}, \ce{aq}) ...
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How is hydration free energy of a solute measured experimentally?

I am reading a paper (Shirts, M. R.; and Pitera, J. W. and Swope, W. C. and Pande, V. S. J. Chem. Phys. 2003, 119, 5740-5761). Near the beginning of the paper (page 5745), the authors state: ...
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When is it okay to use $Q=mc\Delta T$, is this equation only for calorimetry questions?

When is it okay to use $Q=mc\Delta T$, is the equation only for calorimetry questions? When a question talks about heat how do I know if i'm measuring $\Delta H$ or Q?
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196 views

Spontaneous inequilibrium in a gas in an isolated system?

Can an isolated system(of several phases) in equilibrium by itself move out of equilibrium? if a system contains for example an inflammable gas dispersed with another combustible gas such that the ...
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489 views

Measuring Thermodynamic Stability

We can predict whether a reaction can occur spontaneously by calculating the change in Gibbs' free energy. I was just wondering whether there is any general measure of the thermodynamic stability of ...
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967 views

Hot and cold air interaction in a sealed environment

What would happen if air heated to 1200 degree's Fahrenheit in a sealed environment was injected with colder air? No specific pressure defined yet just a general idea of potential interaction between ...
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520 views

Influence of solubility on the complexation constants at different pH values

Given some small chemical compounds whose solubility varies with pH, and in the case of compounds that can form complexes, I have seen that the complexation constant varies with pH. I think there ...
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96 views

Nitrogen triodide energetics

Ammonia has a heat of formation of $-46 \:\mathrm{kJ/mol}$ (which means that it's formation from the elements releases heat). When mixed with iodine at room temperature, it makes nitrogen triodide (...
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119 views

Is it possible to form bubbles of ionized hydrogen and ionized oxygen under the right pressure/temperature conditions during electrolysis of water?

When we run a current through water (pure or not), $\ce{O_2}$ forms at the anode while $\ce{H_2}$ forms at the cathode. If I understand correctly, as water is already slightly ionized, $\ce{H}$'s snap ...
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337 views

Software for chemical reaction simulation in ICE

I want to study what happens in a internal combustion engine in which fossil fuels are mixed along with other chemical additives. Example: Acetone drastically reduces surface tension. Most fuel ...
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2answers
732 views

Calculating heat capacity of a calorimeter

I am struggling on this question : The heat of neutralization of $\ce{NaOH}$ and $\ce{HCl}$ is $-57.1\:\mathrm{kJ}$, calculate the numbers of moles of $\ce{HCl}$ and if $x$ moles of $\ce{HCl}$ were ...
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Difference between thermodynamic and kinetic stability

What is the difference between thermodynamic and kinetic stability? I'd like a basic explanation, but not too simple. For example, methane does not burn until lit -- why?
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What is a pure substance?

I found as I was preparing to teach "Introduction to thermodynamics" that there are varying definitions or examples of pure substances. For instance the text book I have to use "Thermodynamics an ...
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What defines matter's phase at room temperature?

So, a simple question: what makes neon a gas; what makes water liquid; what makes plutonium-238 a solid at room temperature? Of course, the phase is determined by the excitation of the molecules, but ...
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224 views

Lennard Jones liquid vapor phase transition

I am trying to generate a phase diagram of pressure versus temperature in a NPT ensemble using molecular dynamics method. I am using the Lennard Jones potential with 108 particles and Berendsen ...
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1answer
266 views

Source for thermodynamic and/or transport properties

I'm working on some combustion problems using Cantera and I can't find references for the thermodynamic or transport properties for many of my chemical species. I'm looking for NASA-7 or NASA-9 curve-...
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2answers
548 views

Non-Commercial Thermal Insulation

I am trying to create a small 10 to 20cm cube that can conserve the heat in 100 to 200ml of 60-90c water in a small Pyrex glass for about an hour. The problem is that I can not use commercial ...
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Why can dissolution reactions (e.g. dissolution of calcium chloride) be exothermic?

Dissolution reactions are normally endothermic, and crystallization reactions are normally exothermic, but there are some exceptions -- such as the dissolution of calcium chloride. Why is this so?
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Maximum temperature attainable by thermite reaction

In the thermite reaction $$\ce{2Al(s) + Fe2O3(s) -> 2Fe(l) + Al2O3(s)}$$ what is the maximum temperature attainable by the products? Assume reactants at $25\ \mathrm{^\circ C}$ and $1\ \mathrm{...
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Is an explosion merely an exothermic reaction?

An exothermic reaction is apparently one that releases energy to it's environment. According to Wikipedia, an explosion is a rapid increase in volume & energy. Does this mean that an explosion is ...
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1answer
678 views

Determining enthalpy and internal energy of formation for potassium superoxide

Given $2.14\ \mathrm g$ of $\ce{K(s)}$, determine $\Delta H^\circ_\mathrm{f,m}$ and $\Delta U^\circ_\mathrm{f,m}$ for $\ce{K2O}$. We know: The calorimeter's constant: $1849\ \mathrm{J\...
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486 views

Find mass of CO₂ and heat released per minute in a combustion reaction

I am not sure where to start with this problem. I know that $\small q = mc(T_f-T_i)$, but that seems like it would not help here. I think I need to balance the equation, but I am not sure how the rate ...
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3answers
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Looking for a safe exothermic reaction [closed]

Is there an exothermic reaction which produces 1 to 2 minutes of heat at around 175 degrees Fahrenheit, no toxic gasses and is considered to be more or less safe?
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1answer
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Should I use specific heat to calculate how much fuel is required?

Question: A backpacker wants to carry enough fuel to heat $\pu{3.0 kg}$ of water from $\pu{20 ^\circ C}$ to $\pu{100.0 ^\circ C}$. If the fuel he carries produces $\pu{36 kJ}$ of heat per gram when ...
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769 views

Why is bread warm at room temperature?

If I buy a loaf of freshly-made bread and leave it out at room temperature for a day or two, when I reach into the bag the air inside is much warmer than the rest of the room. Why?
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86k views

How do you calculate molar specific heat?

I know how to calculate the specific heat, but not molar specific heat. What is molar specific heat and how do you calculate it?
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Calculating entropy: why consider a reversible path?

I am reading up on entropy in a textbook and I got confused by this: It says that to calculate the entropy for an irreversible process using heat flow, one must imagine the reversible process in ...
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3answers
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What are the chemical reactions behind fire?

I've always wondered what the chemistry behind fire is. What are the basic chemical reactions behind a simple wood fire, and how do they manifest into this phenomenon?
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12k views

Is there a way to calculate how fast water will cool?

Is there a way to calculate how fast water will cool if you know the water's starting temperature and temperature of the environment that you put it in, such as a freezer?
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3answers
8k views

Chemical reactions with a room-scale cooling effect

Are there chemical reactions that could cool down an average sized room by a noticeable amount (say 5 °C)? I would like to investigate if it is possible to have a situation where I can mix 2 ...
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1answer
3k views

Is “ice point” the same as “freezing point”?

I am using an old book and they almost use both terms interchangeably sometimes. Do they mean the same thing? Similiarly for "steam point" and "boiling point"
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3answers
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Methane seems to dissolve more readily in cold water. Why?

When you are diluting air in the system and/or properly evacuating it, you must consider water temperature. Methane is completely dissolved in water at 42 degrees Fahrenheit (5.5 C) but can be ...
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1answer
44k views

Calculating the heat capacity of a calorimeter

I've been struggling with this problem that I can't seem to figure out. I think I know how to solve it but I think there's missing information. The combustion of 1 mole of glucose $\ce{C6H12O6}$ ...
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702 views

What is known about the phase of matter at very high temperature and enough pressure?

Are there theoretical reasons for or against the existence of materials that will not become solid at some fixed, sufficiently large temperature when enough pressure is applied? Or is this even the ...
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standard reference for thermodynamic properties?

I'm a non-chemist attempting to put together a chemistry paper. Up to now I've got my thermodynamic data from various random pdf files found on the web, together with Wikipedia. Now that the paper is ...
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1answer
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How to calculate entropy change for a gas reaction using $S^\circ$?

I'm calculating molar changes in thermodynamic properties due to reactions between gasses (assumed to be ideal gases). I can calculate $\Delta H$ easily enough, because it's just $\sum_i \nu_i\...
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How can I compute the temperature change from the de-excitation of excited particle species?

The motivation for the question in the title is that I have some formula given, $$\Delta T=\frac{3410\ \gamma_{O_2}}{2.5+\gamma_{O_2}},$$ where $\gamma_{O_2}$ is the molar fraction of oxygen in a ...
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What is the difference between temperature and thermodynamic temperature?

My course book says that kelvin is the unit of thermodynamic temperature, then what is the difference between temperature and thermodynamic temperature.
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777 views

Deliquescence/efflorescence: How can I convert between salt concentration and RH?

I am looking at two phase diagrams, one has axes of $T$ and $\%\ce{MgClO4}$ in a $\ce{H2O-MgClO4}$ mix, and the other has axes of $T$ and relative humidity. The authors of the second phase diagram say ...
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903 views

Where can I obtain tables of P-V-T/compression factor data?

Some recent research I'm dealing with has required me to look for tables of experimental pressure/volume/temperature values (equivalently, a table of compressibility/compression factors in terms of ...
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180 views

Difference between non-thermal and thermal ionized gases

Why or when does non-thermal plasma become thermal? How do we know before hand if the ion temperature will differ from the electron temperature, on what parameters does it depend - where is the ...
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2answers
12k views

Temperature dependence in absorption spectroscopy

What are some qualitative guidelines one should know regarding the temperature dependencies (of the gas and maybe the radiation, if that makes sense) for an absorption spectroscopy measurement? How ...
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1answer
255 views

Negative retention for chloride in hydrolysate filtration

I tried to fractionate proteins as a function of their size with an ultrafiltration membrane. I observed a higher concentration of chloride in my permeate than in my feed or retentate. The proteins do ...
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246 views

What is the difference between an ionic and molecular activity model? (Example: Diopside-Hedenbergite)

Original question: When looking at a Diopside-Hedenbergite solid solution, what is the difference between an ionic and molecular activity model? Why does the moleclar model yield higher values? Post-...
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What is a rigorous definition of gas volume, and how is the Van der Waals equation derived?

I am confused about the justification for the corrections to the ideal gas law in the Van der Waals equation: $$p=\frac{nRT}{V-nb}-a\left(\frac{n}{V}\right)^2$$ I understand that the equation ...
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2answers
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Is the specific heat capacity of liquid iron constant?

Does liquid iron have a constant specific heat capacity? Everywhere I've looked (save one sourceless online reference to $c_p = 611\ \mathrm{J\ kg^{–1}\ K^{–1}}$ here), I find no value listed for ...
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Is enthalpy additive in mixing?

When mixing two fluids of different composition at constant pressure when no heat can escape, is the enthalpy additive? If not, how to compute the enthalpy of the mixture resulting from mixing two ...
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How does dimethylsulfoxide serve as a cryoprotectant?

In cell culture, dimethylsulfoxide (DMSO) is added to prevent the formation of ice crystals which may lyse the cells. Exactly how does dimethylsulfoxide act as a cryoprotectant?
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Retention of surface texture after combustion

Just some while ago I was burning a box of cardboard in my backyard and I saw a very curious phenomenon. I saw that as the cardboard box started burning it started to curl. Up after a while as I ...
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Why is slush hydrogen at the triple point?

Slush hydrogen is a mixture of liquid and solid hydrogen at the triple point considered as a possible vehicle fuel. What is the need of having it at the triple point? Couldn't any other set of ...