Questions tagged [heat]

For questions about heat - a form of transfer of energy from one body to another or from one body to its surroundings. Also see these tags: [thermodynamics], [enthalpy], [energy], [temperature].

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Why are IUPAC's definitions of exo- and endothermic disconnected from the direction of heat flow?

I'm wondering if anyone can provide a rationale for IUPAC's definitions of exothermic and endothermic, since they disconnect these terms from the direction of heat flow. Specifically, here are IUPAC'...
theorist's user avatar
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Seeking titanium compound, melting point <1600 °C, decomposes to TiO

The title says it all. I’m new to glass making, and I need a titanium compound that will render me $\ce{TiO}$ through decomposition, and has a melting point under 1600 °C. Hopefully I can get one ...
Joseph's user avatar
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Calcium chloride + starch desiccant packs inside PPE for ebola workers?

(First question on stackexchange, apologies for any faux pas) Ebola workers get drenched in sweat while working inside their personal protective equipment. There's a discussion happening over on ...
Jason Holt's user avatar
4 votes
2 answers
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Entropy change during electrolysis of water

Consider the electrolysis of water reaction: $$\ce{H_2O -> H_2 + 1/2O_2}$$ At room temperature and atmospheric pressure, the change in enthalpy of this reaction is $\Delta H = \pu{+286 kJ mol-1}$. ...
SalahTheGoat's user avatar
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Theoretical temperature change in lime hydration

Calcium oxide (quicklime) and water have an exothermic reaction $\ce{CaO + H2O \rightarrow Ca(OH)_2} \quad \quad \Delta H^{\circ}_f=-65.3 \; \mathrm{kJ \cdot mol^{-1}}$ Assume that I have 1 kg of ...
jannekem's user avatar
4 votes
1 answer
173 views

How can the reaction heat be ignored in an energy balance?

I have received from my professor the following (summarized) problem: A first-order exothermic reaction $\ce{A->B}$ took place in a typical tubular plug flow reactor (PFR). The tube was cooled to a ...
J Faller's user avatar
3 votes
0 answers
155 views

Meaning of chemical potential in chemical reactions

In my thermodynamics course, we introduced the chemical potential as a modification of the first + second law of thermodynamics in the case of a system that can exchange particles with its ...
Peter's user avatar
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How does the surface to volume ratio of ions and their distribution in solution compare to that of suspended nanoparticles in nanofluids?

I am interested in understanding the heat transfer capabilities of fluids. Nano-fluids are suspensions of nanoparticles (1-100nm sized particles) in a base fluid, often water, oil or glycol. These ...
R2B2's user avatar
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Which term for heat energy in calorimetry is correct in scientific usage?

In calorimetry several terms are interchangeable: Lower Calorific Value Lower Heating Value Net Calorific Value Net Heating Value The following terms also appear to have identical meanings: Higher ...
Agriculturist's user avatar
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Azobenzene heat trapping

Azobenzenes trap heat when exposed to sunlight due to the principle of photo-isomerism. But this occurs in nanoseconds. I was wondering if we can store this heat for hours and utilize this later on. ...
Asad's user avatar
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How does heat and/or boiling remove vitamin C?

The www is full of crackpot claims about how various food treatments alter their nutrition content and it makes finding actual science very difficult. I am specifically interested in the vitamin C ...
ProfRob's user avatar
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energy efficiency, transformation from chemical to thermal energy, for district heating plants

If I have a system in which I introduce $\mathrm{100~e.u.F}$ (energy units) derived from chemical energy (i.e. fuel) and generate thermal energy to heat water what are e.u. absorbed by water? I.e. the ...
Luther's user avatar
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Can heat cause the excitation of argon

Can argon be excited by heating? I work with a process that involves heating titanium to 500c-1000c in an argon environment. On our camera, the material looks purple when heated, the same shade as ...
Andriy's user avatar
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Is heat treatment the only way to increase grain size in steel?

Heat treatment is a well-established method for increasing grain size in steel. Is there any other approach known to man? I cannot seem to find anything via web search.
artist_and_not_EE_by_training's user avatar
2 votes
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Prigogine vs. Bronsted and the minimum entropy production principle

I apologize for the length of this question that was asked here prigogine-bronsted but got no reply; anyhow, Bronsted's name is much better known among chemists than among physicists... Prigogine's ...
hyportnex's user avatar
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Would a PNG geyser work on biogas?

I am trying to understand if a water heater designed to run on piped natural gas (PNG) could be powered by biogas without any modifications. Typically, these geysers have a battery-powered ignition ...
Chethan S.'s user avatar
2 votes
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At what temperature does a polyester release toxic gases?

I've bought a "Shrinky Dinks" printable sheets and now I'm feeling unsure about using it since I've read that heating polyester materials may be very harmful for health, and the final ...
Blak0's user avatar
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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 ...
David Lu's user avatar
2 votes
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416 views

Does specific heat capacity of the container have an effect on the exactitude of a calorimetre?

I'm doing a lab on what is the best material for a calorimetre. I chose glass, aluminum, styrofoam cup, paper/cardboard cup and a plastic cup. I've found that the cardboard cup was the best followed ...
Cyril O'Brien's user avatar
2 votes
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658 views

Calculate work done by burning benzoic acid exposed to the free air

I'm self-studying and can't solve this problem in Ball's Physical Chemistry. Now, the errata shows that the answer in the book is not correct; still, I can not make sense of it. $(2.55)$ Benzoic acid,...
Orange Mushroom's user avatar
2 votes
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1k views

Which cup of tea cools down more quickly?

There are 2 cups (both cups are identical) of tea which are served at the same temperature. Assume that the walls of the cup to be non-heat conducting. Which cup of tea cools down faster, a full-...
Kaustubh Shankar's user avatar
2 votes
0 answers
135 views

Heat capacity of mixtures is higher than their pure contituents?

I'm currently studying the effects of how changing mixed-refrigerant compositions effects their heat capacity. Surprisingly, my data suggests that some combinations of mixed-refrigerants have heat ...
Joey's user avatar
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Formation: So much heat, where does it all go?

I was comparing heat of formation numbers with specific heat values, and the numbers look really weird. Take a typical example like magnesium fluoride. Its $\Delta H$ is -1124 kJ/mol and its heat ...
MackTuesday's user avatar
2 votes
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2k views

Heat capacity during state change

I read that the heat capacity of water when it is at 100 °C or 0 °C is infinite because all the heat given to it will not be used to increase temperature but to change the state. I am unable to ...
Mahathi Vempati's user avatar
2 votes
0 answers
1k views

How are pressure vessels heated?

I'm working on a project in which I'll be dealing with pressure vessels. As of now I've drawn/conceptualized everything on theory basis. The diagrams are made on the basis of theory, but then I came ...
george mik's user avatar
1 vote
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140 views

Chemical equation of wood to charcoal pyrolysis

The equation for the perfect burning of wood is approximately: $$\ce{C_xH_yO_z + VOCs + O2 -> CO2 + H2O + volatiles + heat}$$ Where $\ce{C_xH_yO_z}$ represents the cellulose and lignin and VOCs are ...
Adrien Hingert's user avatar
1 vote
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66 views

How can the heat equation be used to model temperature vs time in a solubility experiment?

Background: I am doing experiments trying to map the practical solubility of a certain chemical species called an "activator" solution. This solution is essentially a sequential mixture of ...
Hendrix13's user avatar
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Enthalpy/Temperature change in a chemical reaction

I was wondering how exactly absolute temperature change in a chemical reaction could be calculated. For example, consider this reaction: 3H₂+N₂→2NH₃, ΔH=-46kJ/mol (298.15K) Assuming the given reaction ...
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Cooling down from −78 °C to −88 °C without cryogenics

Say I have a gas cylinder with nitrous oxide and cool it down to −78 °C with dry ice. Is there an endothermic process/reaction that would extract the remaining heat from $\ce{N2O}$ and bring it down ...
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Verify heat produced by flame using enthalpy of fomation

I'm simulating using a CFD solver a pure oxygen/methane flame. However, I doubt that the combustion model does not produce enough heat. The heat from reaction is defined by $S_h=-\sum_{j} \frac{h_j^0}{...
Yann's user avatar
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110 views

Help in understanding first way of changing the state of system

There is a statement in my book: THERMODYNAMICS One way: We do some mechanical work, say $\pu{1 kJ},$ by rotating a set of small paddles and thereby churning water. Let the new state be called $\...
Srijan's user avatar
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Strange Distillation Behavior

I was attempting a fractional distillation with 1mL water and 1mL propylene glycol, and I’ve been encountering strange behavior with the heating of the mixture. The heating curve shows strange “spikes”...
COsborne's user avatar
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Does fractionation use enough heat to destroy nutrients in Coconut Oils when seperating the MCT oils?

We have recently been giving MCT (medium-chain triglyceride) oil to our dogs in place of Coconut Oil as from what I understand the majority of the benefits of Coconut Oil comes from the MCT's ...
Brett's user avatar
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Boilling colloidal silver?

I have some colloidal silver that i bought from a shop. It is 18ppm, however, I need a higher PPM and I can't seem to buy it anywhere where I live. If I boil this colloidal silver, would it make the ...
bruzza42's user avatar
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351 views

Cis-Trans Isomers Heat of Combustion

Consider the 4 cis-trans isomers for the above compound. In what way would the cis-trans isomers affect their heat of combustion. I think that if the substituents are on alternating sides of the ...
gauri agrawal's user avatar
1 vote
0 answers
557 views

When Cp = Cv + R

So in a physics test question, there was this question when is $C_p$ not $C_V + R$? And I wrote: when number of molecules change. Because the derivation of above formula comes from $nC_p\,\mathrm dT -...
Newbie Developer's user avatar
1 vote
0 answers
66 views

Determining heat capacity of gasses

I need a little help on answering a question which popped into my head while I was reading about gas laws: Suppose that I have three canisters, each holding a different gas of unknown identity [...
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Derive expression for average heat flux in heat exchanger

The single-tube heat exchanger is used to increase the temperature of fluid I from $T_{b1}$ to $T_{b2}$. The heating oil (fluid II) used for this task enters at temperature $T_{02}$ and leaves at ...
lotte07's user avatar
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Simplifying temperature profile

I am given the temperature profile below and the two equations: $$Q = (2\pi R_0)LU_0(T_{1\infty}-T_{2\infty})\tag1\label1$$ $$\frac{1}{U_0R_0} = \frac{1}{h_1R_0} +\frac{\ln(R_\mathrm a/R_0)}{k}+ ...
lotte07's user avatar
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820 views

What is the specific heat and latent heat of an ethanol-water mixture?

How do I find the specific heat and latent heat of ethanol-water mixture? Let’s say the mole fraction of water is 0.3 and ethanol is 0.7. I am working on a project and needed values for these and ...
user185692's user avatar
1 vote
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914 views

Does iron in water become visible when being heated?

I'm using ground water to provide my daily needs: Laundry, bath, toilet, ... I don't use it as drinking water, but I do cook with it. What I noticed is that when using the water cold it appears as ...
Mech_Engineer's user avatar
1 vote
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794 views

How much water evaporates during a given time?

I read some questions such this for example and I asked me another question. Instead of only calculate how much time does it takes to have a cup of tea at room temperature, I'm asking how much time ...
ParaH2's user avatar
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1 vote
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Reaction of Phenolic acids

I'm puzzled as to what can happen to phenolic acids when they are heated. (Chemistry, not health or food science) How do they dehydrate? Do they form anhydrides? Also, is it possible for the ...
user30677's user avatar
1 vote
0 answers
74 views

Hot-side and Cold-side rechargeable chemical compound

I am wondering if such a chemical/material exists which, upon triggering, becomes cold on one side and hot on the other in which after all the chemical bonds are broken/built (however it would work), ...
Relative0's user avatar
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Endothermic Reaction with Specific Details

I need some information for a book I'm writing. Let's say you're in a confined space, about 8 feet by 8 feet. The area is being heated externally slowly (a few degrees a minute) to about 3,100 ...
Kate Comstock Andjelkovich's user avatar
1 vote
0 answers
783 views

How to calculate enthalpy change of neutralisation - what mass?

How to calculate enthalpy change of neutralisation - what mass? I made an experiment where I reacted 100ml HCL 2M with 100ml NaOH 2M in 1300ml Water, and got a temperature change dT. My question is ...
Adam's user avatar
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Estimate inflammability of ABS?

I am studying some electrical components and particularly Raspberry Pi 2 official cases. Their manufacturer says that they consists of ABS (Acrylonitrile butadiene styrene) when I ask if their ...
Léo Léopold Hertz 준영's user avatar
1 vote
0 answers
2k views

Entropy change of surroundings

The entropy change of a system is given by $$\mathrm dS=\frac{\mathrm dq_\text{rev}}{T}$$ which at constant temperature is $$\Delta S=\frac{q_\text{rev}}{T}$$ I also learned that the entropy change ...
carbenoid's user avatar
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118 views

Electrode/solution interface : What's the difference between the electrochemical Peltier heat and the heat caused from the overpotential?

In principle heat effects caused by the passage of an electric current might arise from: electronic peltier effect at the junction of electrode/solution level, Joule effect due to solution resistance, ...
LanaLane's user avatar
1 vote
0 answers
93 views

How can I use sunlight to heat a RBF and reflux a reaction?

This may seem like a off topic question but I really need help on it. I am currently working on a polymerization reaction in which I'm breaking down plastic polymers into smaller molecules. However, ...
Daniel Kosciuszko's user avatar