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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Calculating Enthalpy Change from Calorimetry [closed]

What calculating the enthalpy change of a reaction, for example 5g of CaCl2 dissolving in 100 mL of water, is m the mass of water or the mass of water plus the mass of the salt. q = (105g)(4.18)T or q ...
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Does heat increase the hydrolysis of urea hydrochloride?

The preparation of ammonium chloride by reacting urea with HCl produce urea hydrochloride the reaction take too much time to get ammonium chloride depending on ratios. So can heat increase the ...
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What do they mean with temperature in the formula for enthalpy?

I'm studying enthalpy and I'm having a real hard time trying to conceptualize it. I can do the exercises and know the formulas but I feel like I lack an understanding of what it actually is. One of my ...
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3 votes
2 answers
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What does the heat capacity really represent? [closed]

According to Wikipedia, heat capacity or thermal capacity is a physical property of matter, defined as the amount of heat to be supplied to an object to produce a unit change in its temperature:$$C = \...
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why does sodium chloride in water dissolve/precipitate with little heat, or indeed, at all? [closed]

Sodium and chlorine presumably react together strongly, which is why the solid product is stable and takes a lot of energy to break the bonds formed, and to melt. According to the Wikipedia, melting ...
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How can the reaction heat be ignored in an energy balance?

I have received from my professor the following (here summarized) problem: A first-order exothermic reaction A->B takes place in a tubular reactor (typical PFR). The tube is cooled to a constant ...
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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 ...
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Difference between the specific heat capacity of potassium chloride solution and sodium chloride solution

I am curious about the difference between the specific heat capacity of a potassium chloride solution (KCl + water) and a sodium chloride solution (NaCl + water) - particularly the specific heat ...
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How do I calculate the maximum temperature of an exothermic NaOH reaction in water?

As the title suggests, let's say I want to make a 1 L 14M NaOH solution. For this I'd need: (14 mol/ L) x 1 L x (39.99 g / mol ) = 559.86 g NaOH(s) {solute} ~1 L H2O (approx) {solvent} The ...
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What is heat bath here?

At the beginning $\pu{1 mol}$ of air is compressed to $\pu{3 atm}$ at a of temperature $\pu{523 K}$. After a random process, the pressure of the air equates to $\pu{1 bar}$ at a temperature of $\pu{...
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3 answers
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Do exothermic reactions also absorb heat?

As I have read that every reaction(endothermic or exothermic)requires activation energy. So is it correct to say that even exothermic reactions absorb heat? I am asking this because it is always ...
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Burning wood with ammonium chloride

There is a method where you use a water solution of ammonium chloride to paint some pattern or write some text on a piece of wood and then blow on it with a heat gun. The result is that the pattern ...
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What is the difference between heat of reaction (q) and enthalpy of reaction ∆H?

I am confused as I can’t understand the difference between the thermodynamic terms q and ∆H. In my book,“general chemistry” by Ebbing and Gammon,it is stated that at constant pressure Qp=∆U+P∆V=∆H. ...
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Exothermic temperature rise on NaOH + Methanol

When mixing NaOH (w/w 0.05%) with methanol, there is an increase of temperature around 20 C I wonder if we keep this ratio in large amount of methanol, will there be any spike in temperature increase ...
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Calculating Enthalpy of formation versus Calculating Enthalpy of a reaction not occurring at standard conditions

My understanding of Hess's law and its use in determining the change of enthalpy of a reaction has been challenged recently. Up until recently, I thought that the only way to calculate a chemical ...
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Literature recommendation - non-stationary heat transfer in porous solids

I am trying to calculate a non-stationary heat transfer to a porous spheres by conduction. These spheres are placed in a thin metal tubes with a known heat capacity. Hot/cold air (or similar gaseous ...
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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 ...
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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 ...
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1 answer
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why can water heated to a certain temperature in microwave explode when removing cup , bowl etc to room temperature air? [closed]

Studied a lot about $\mathrm{pH}$ , molecule dipoles properties $\ce{H2O}$. never saw anything along lines of energy storage, except ice contains heat energy , ionization of water always happens. ...
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Liquids with high specific heats?

I am wondering if there are any liquids other than water that have relatively high specific heat capacities. The tables of specific heats of common substances I have found do list ethanol (2.376 J/(g °...
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Is the heat (or work) of the system always equal and opposite to that of the surroundings?

I know energy must always be conserved by the first law of thermodynamics, but is there ever a scenario in which a system say releases some amount of energy as work, and the surroundings gains equal ...
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example of endothermic luminescence?

Someone posed an interesting question to me the other day: is all production of light accompanied by the generation of heat? I have found that the question as posed invites vague answers, so I thought ...
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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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Heat of Sublimation of GaAs and SiC

I am trying to find values for the heat of sublimation of GaAs and SiC, but can't find anything. I also tried searching for the heat of fusion and vaporization, to calculate the heat of sublimation ...
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Dry ice sublimation rate in water

As I got some a finger sized of dry ice in water, it started to bubble vigorously as expected and gave off a lot of smoke. But after 3 minutes or so, the rate of sublimation seems to slow down a lot, ...
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What would happen if I increase the pressure and temperature of a gas present in a container

Assume the gas to be a real gas and the container to be made of diamond or anything stronger than that. Take the amount of gas to be 2mL and the pressure is increased with the help of strongest ...
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Boiling of ammonia water [closed]

L̶e̶t̶'̶s̶ ̶m̶a̶k̶e̶ ̶i̶t̶ ̶s̶i̶m̶p̶l̶e̶.̶ ̶I̶ ̶h̶a̶v̶e̶ ̶a̶ ̶p̶o̶o̶l̶ ̶o̶f̶ ̶a̶m̶m̶o̶n̶i̶a̶ ̶w̶a̶t̶e̶r̶,̶ ̶a̶n̶d̶ ̶w̶h̶e̶n̶ ̶I̶ ̶h̶e̶a̶t̶ ̶t̶h̶e̶ ̶a̶m̶m̶o̶n̶i̶a̶ ̶w̶a̶t̶e̶r̶,̶ ̶a̶m̶m̶o̶n̶i̶a̶ ...
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Why is the enthalpy change of an ideal gas a function only of temperature?

While teaching us thermodynamics our chemistry teacher told us that enthalpy change of a real gas is a function of temperature, pressure etc. but the enthalpy change of an ideal gas is only a function ...
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What can happen to overheated aluminum cookware?

I accidentally overheated an aluminum espresso maker, to around 250-300° C in my estimation, but it might be even higher - I didn't measure, though. After research, I found that the material used is ...
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Double boiler apparatus with no loss of water?

Is there an apparatus that operates like a double boiler, but loses no steam? In other words, in a normal double boiler the steam is allowed to escape, so energy is lost and the boiling pot must be ...
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How to thermally insulate beaker glass on hotplate?

I bought a magnetic stirrer with a hot plate almost identical to this one. I am trying an experiment where I need to heat the beaker/mixture to about 100 degrees C. However the mixture/beaker is ...
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6 votes
3 answers
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Is it possible to increase the internal energy of an ideal gas in an isothermal process?

Ideal gas is the one in which there are no attractive or repulsive forces acting and hence its internal energy is due to kinetic energy of its molecules. We may then say, for an ideal gas internal ...
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12 votes
1 answer
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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 ...
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Heat released at constant pressure and temperature and heat released at constant density and temperature

Is there a relation between heat released at constant pressure and temperature and heat released at constant density and temperature? I was reading some books on propulsion and combustion, and the ...
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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 $\Delta H = \pu{+286 kJ mol-1}$. ...
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2 answers
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Calculate Specific Heat given initial temp, final temp and equilibrium temp [closed]

I would appreciate if someone could enlighten me on this question. Question: A metallic object with a mass of 2 kg at 50ºC is placed in 10 L of water at 20ºC. When the thermal equilibrium the ...
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3 votes
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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 ...
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6 votes
2 answers
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A possible reaction of heating Terephthalic acid

There is no reaction of terephthalic acid heating effect on the internet (at least Wikipedia). I have written the most probable reaction possible as per my knowledge. Please tell if it is spontaneous ...
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Change in Enthalpy when Pressure is constant

Okay so let me start from the beginning. I know that $ΔH= ΔU + p ΔV$ ( at constant pressure). Expanding $ΔU$, $$ΔH= q + pΔV + pΔV ~~~~~\text{(q at constant pressure)} \tag{1}$$ Next my chemistry ...
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Why is enthalpy and not heat released by system used while calculating entropy of surroundings?

While finding the sum of change in entropy of the universe and thus defining Gibbs free energy, why is the change in entropy of surrounding the negative of enthalpy of the system divided by the ...
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Relation between enthalpy and internal energy for chemical reaction at constant volume

Question The combustion of benzene(l) gives $\ce{CO2(g)}$ and $\ce{H2O(l)}.$ Given that the heat of combustion of benzene at constant volume is $\pu{-3263.9 kJ mol-1}$ at $\pu{25 ^\circ C}$; heat of ...
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7 votes
1 answer
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Does all fire only emit light on its outermost shell?

This question is about light emission, which may overlap with physics, but I am most interested in combustion and types of flame (incandescence, petrochemical fuel flames, nuclear ractions). Consider ...
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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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What did I do wrong in my temperature change calculations?

I am doing an online assignment where I am being asked to find temperature change but there is something wrong in my calculations as I am getting the answer wrong. Can someone help me figure out where ...
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-1 votes
1 answer
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Cinnabar decomposition by heating optional method?

Is it possible to decompose cinnabar into $\ce{Hg}$ and $\ce{S}$ instead of $\ce{Hg + SO2}$ with roasting and heating. What conditions need to be satisfied in the new method?
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In a heating curve, when it is plateau, where does all the energy go since the temperature does not get higher? [closed]

So between the change of phases within the matter(solid liquid gas), the temperature reaches a plateau, no matter how much heat you add to it, it just stays the same. Where did all those energy go?
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Why does higher temperature affect the rate of electrolysis?

I understand that more heat energy= higher rate of electrolysis, but can someone explain using higher-level terms why this occurs and if there are any theories or rules that explain this?
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3 answers
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What is non toxic to fish, has a low freezing point, and floats on water?

I am looking for a liquid that floats on water that will prevent the water from freezing (or at least slow it down). The application would be a small area (less than a square foot). It has to be non-...
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6 votes
3 answers
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Why is the sum of two inexact differentials exact?

From the first law of thermodynamics, $\mathrm{d}U = đQ + đW$, where $\mathrm{d}$ represents an exact differential and $đ$ an inexact differential. Exact differentials correspond to state functions ...
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Any examples of reactions where simpler molecules are combined into more complex ones and are endothermic at the same time? [closed]

Can you name examples of reactions that are endothermic and simple molecules are combined into more complex ones at the same time? Like what plants do they take heat and sunlight and they synthetize ...
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