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].

68 questions with no upvoted or accepted answers
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11
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145 views

Constraints on pyrotechnic explosives that won't detonate spontaneously at 500 °C when landing on Venus?

The Space Exploration SE question Premature detonation of explosive bolts when landing on hot Venus? explains the need for and widespread use of pyrotechnic fasteners and cable cutters for Mars ...
8
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458 views

Does heating potato starch destroy its resistant starch?

Resistant starch, as found in potato starch, is supposed to have health benefits. There are differing opinions on whether or not heating potato starch destroys the resistant starch in it and thereby ...
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168 views

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'...
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133 views

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 ...
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269 views

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 ...
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2answers
245 views

Heat transfer through layered wall

An electrical heater is placed between two layers of insulation. The three layers (the heater and the two layers of insulation) have the same thickness. The figure below shows different temperature ...
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3k views

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 ...
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51 views

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 ...
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122 views

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 ...
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65 views

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. ...
3
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1answer
964 views

Why add specifically hot solvent during recrystallization procedures instead of heating it up after?

Recrystallization methods that I have seen online and in manuals involve adding a minimum amount hot solvent to the solid mixture. Is there a reason I should do this instead of adding an equivalent ...
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458 views

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 ...
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183 views

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 ...
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39 views

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 $\Delta H = \pu{+286 kJ mol-1}$. ...
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112 views

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 purpose of this ...
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198 views

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 ...
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264 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 ...
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521 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,...
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887 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-...
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121 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 ...
2
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81 views

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 ...
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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 ...
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947 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 ...
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48 views

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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25 views

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}{...
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43 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 $\...
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34 views

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”...
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143 views

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 ...
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146 views

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 ...
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135 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 ...
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262 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 -...
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59 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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80 views

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 ...
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34 views

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}+ ...
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363 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 ...
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1answer
70 views

Where can I find the total enthalpy and heat of dissolution in water of a given components?

I don't really have a background in chemistry but I'm actually studying in aerospace engineering, sorry if this question may seem trivial. I am interested in the decomposition process of the hydrogen ...
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17 views

Plasma cleaner Increasing pressure in vacuum

We have a plasma cleaner, in order for the plasma to be created there has to be around 200-300 mtorr. As soon as we turn the plasma, the mtorr instantly goes up but the vacuum line is still active. ...
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595 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 ...
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615 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 ...
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50 views

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 ...
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68 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), ...
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63 views

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 ...
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767 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 ...
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60 views

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 ...
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0answers
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 ...
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109 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, ...
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0answers
300 views

How quickly will steel lose structural strength from a heat flash?

I want to know if a sustained jet fuel burn around steel has the ability to make the steel structurally unsound. It seems like any applied heat that effects steel will be a kind of "heat flash": a ...
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0answers
90 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, ...
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0answers
36 views

Suggestions for research into different fluids in heat pipes

I'm doing some research on heat pipes (check here for wiki). One of the things I'm planning to do is try some different fluids in the pipes. Water (commonly used) has a freezing point that's too high, ...
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816 views

Taking Castor Oil from room temperature to 300 degrees Celsius

I am doing a project where I heat up a container (around 500ml) filed with castor oil at room temperature. I want to add a pressure/safety valve that opens up when the castor oil reaches around 300 ...