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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Change in heat of photosynthesis
Consider a plant that uses the energy it receives from the sun to do work (to undergo photosynthesis) to produce glucose. The minimum amount of work this plant can do to produce 1 mole of glucose is ...
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Determine heat flux from temperature profile
The heating
element and the insulator are of equal thickness L. Heat transfer in
the air film adjacent to the heater is assumed negligible.
I've noticed that I find these type of problem the ...
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Why do unripe papayas taste less bitter after being boiled?
An unripe papaya tastes very bitter if you try to eat it. Actually, the juice that comes from it is so corrosive that it can burn your skin, causing severe pain. I've experienced this first hand when ...
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Is it possible to calculate specific heat capacity of a compound based on its elements' heat capacities?
What the question says. For example, if I knew the specific heat capacities of lithium and oxygen, could I work out the specific heat capacity of lithium oxide with no further information?
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Denaturing of Proteins and Nucleic Acids - Effect of Temperature (Heating vs Cooling)
Heating a protein/nucleic acid will disrupt inter-molecular and intra-molecular forces in the tertiary structure. It will also interfere with the shape of the active site if the protein.
Does this ...
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How can I check if this mystery compound is strontium bromide?
Trying to identify a mystery compound, here are some of my notes, I'm trying to get a second opinion on what it might be!
Observations
Appears as a white powder, some chunks are formed, sticking to ...
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Baking Soda + Oil at high temps
My mom while making Potato chips put some Baking Soda in Oil with it. Just curious to know, it was first time Baking Soda in Oil at that high temperature. Is it safe to eat?
Answer ASAP before my ...
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Thermodynamics of DNA double helix formation?
The entropy of a system decreases when 2 single stranded DNA molecules come together and form a double stranded molecule. For this to occur the total entropy of the universe must increase. Thus, heat ...
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Why is it advised to put a Styrofoam plate under an Erlenmeyer flask?
At school today, we were doing experiments with ammonium nitrate and sodium hydroxide, and mixing them with water into an Erlenmeyer flask (separate flasks, of course). My instructor told us that we ...
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What is the temperature of heat generated from LPG gas?
I'm working on a project and I require around 300-400 degree Celsius of temperature. As of now I'm taking the normal LPG gas that is available in our house for cooking purposes for my project, but I'm ...
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How to determine the specific heat of methanol from calorimeter data?
A $\pu{25.95 g}$ sample of methanol at $\pu{35.6 ^\circ C}$ is added to a $\pu{38.65 g}$ sample of ethanol at $\pu{24.7 ^\circ C}$ in a constant pressure calorimeter. If the final temperature of the ...
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Better understanding the pyrolysis reaction
I'm no chemist, but much of my work revolves around biochar. I've always understood it with the following rough approximation:
$$
\ce{CH2O (dry plant matter) + heat -> black carbon + H2 + CO + ...
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Is the activation barrier of a reaction related to the free energy or heat of formation of its reactants?
The energy barrier for activation appears in the derivation of a bimolecular reaction through collision or transition state theory, but it seems that from looking at diagram such as this one it seems ...
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Are there any nonflammable thermal insulators which can be made at home?
I am trying to build a homemade thermos. It needs to be able to conserve the heat in 125 ml of water for 15 minutes.
However, unlike a normal thermos, it also needs to be able to be heated. What ...
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Current and reversible heat in battery reaction
In the book Battery Technology Handbook by Kiehne [1] (Google Books) on page 21, equation (32):
The reversible heat effect per time unit can be related to current flow, because each multiple of the ...
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Equation for overall heat transfer coefficient
The heat flow (in $[\pu{J/s}]$) through the wall of a tube of length $L$ and inner radius $R_0$ is
$$Q = (2πR_0L)U(T_{1\infty} - T_{2\infty}),$$
where $T_{1\infty}$ is the bulk temperature in the ...
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Aluminium, heat and biological safety
I'm currently working on a really simple project, an ashtray that can stop cigarette combustion.
I planned to put an aluminium block into my ashtray, with some kind of curves or holes in it, in order ...
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Can a reaction of the form A + B → AB ever be endothermic? [duplicate]
I understand that forming a bond between $\ce{A}$ and $\ce{B}$ is an exothermic process, with negative enthalpy, but won't there be energy required to get $\ce{A}$ and $\ce{B}$ close enough together ...
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What's with the weird definition for the Calorie? [duplicate]
I came across this definition for the calorie, which I found... strange:
"The (15°) calorie is the heat required to raise the temperature of one gram of water from 14.5°C to 15.5°C."
Subsequent ...
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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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What causes the difference in heat energy released by combustion for the butanol isomers?
I am currently working on an investigation where I am burning isomers of butanol to test for the heat of combustion values to see which fuel is most efficient. The fuels I am testing are 1-butanol, 2-...
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Why might my limelight experiment have failed and how can I improve it?
I was teaching the lime cycle to some children yesterday. I had a limestone chip (about 10g) held at the tip of a blue Bunsen flame for several minutes. It decomposed and disintegrated but only glowed ...
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What are possible hazards of fog machines?
From a chemistry point of view I would like to learn about possible hazards of fog machines.
Such devices, also called “foggers”, create vapor which appears like fog or smoke. It is used in discos, ...
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Safety concerns - Heating PMMA (acrylic glass) and fluorinated polymers
I have some plastic optical fiber, which consists of a thin core of PMMA (polymethyl methacrylate), covered by a fluorinated polymer.
I would like to heat a bundle of these fibers to ~130 degrees, in ...
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The sign of enthalpy of formation of magnesium oxide
I'm currently doing a lab to calculate the enthalpy of formation for $\ce{MgO}$. However at the moment me and my lab partner are having a disagreement. We've both calculated and agreed upon the same ...
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How hot is elephant toothpaste?
So, I remember in high school chemistry when my teacher combined hydrogen peroxide with potassium iodide and it exploded into a yellowish foam. He said it was an exothermic reaction so it's really hot....
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Ratio between heat tranfer coefficient and thermal conductivity
Consider the Robin boundary condition for the diffusion/heat equation $u_t=a(t)u_{xx}+f(x,t)$:
$$-k(t)u_x(0,t)=h(t)u(0,t)$$
or
$$u_x(0,t)+\frac{h(t)}{k(t)}u(0,t)=0$$
where $k(t)$ thermal ...
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Is it customary to express heat loss as a negative number?
In my chemistry class, we had a problem akin to the following:
If an object with mass bla and specific heat bla is placed into a bla g calorimeter with an initial temperature of bla and a specific ...
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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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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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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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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. ...
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Resultant temperature of mixture
**Question: ** There are 2 flasks of equal volume, connected by a narrow tube of negligible volume, filled with nitrogen gas. When both are immersed in boiling water, the gas pressure inside the ...
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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 ...
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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 ...
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Is this endo or exothermic?
$$\ce{4Fe + 3O2 -> 2Fe2O3(s) + 1625~$\mathrm{kJ}$}$$
This should be endothermic because the energy is in the product. However, if the equation is viewed from the perspective of the reactant, it ...
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What non-toxic non-corrosive liquids are used for heat transfer?
I have a steel vessel placed concentrically within a larger steel vessel, resulting in air-filled annulus (air gap) between the two vessel walls (figure below). Due to the existing vessel construction,...
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How well (or poorly) does natural leather insulate?
What is the general thermal conductivity of animal skin leather?
I understand there are many different animal's skins (cow, sheep, buffalo, deer, pig), but in general, does natural leather insulate ...
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Confused why delta ∆Q and dQ don't make sense for heat Q
In my chemistry teacher's notes, some notations concerning the heat $Q$ are marked as inappropriate.
$Q$: yes
d$Q$: no
$\delta Q$: yes
$\Delta Q$: no
In the second bullet in the screenshot below, ...
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Are the vibrational modes of CO2 active at room temperature?
I was doing an experiment whereby I had to measure the specific heat ratios of certain gases. Carbon dioxide came out to be around 1.3, and checking with the accepted values this is close. My question ...
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What is the substance with the highest specific heat?
I always learned that water has the highest specific heat, but I recently saw that hydrogen has a specific heat as high as $\pu{14 cal g^-1 °C^-1}$ and helium has a specific heat of $\pu{5 cal g^-1 °C^...
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Heat of combustion among substituted cyclohexanes
Arrange in ascending order of heat of combustion:
I know heat of combustion is inversely proportional to stability. Also, to solve I did try making chair conformations of the substituted cyclohexane.
...
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How do I cool my water bottle immediately for an emergency use?
What are the chemicals I can use to cool my water-bottle at once if I'm stranded in a desert and I have only chemicals to cool water?
(I'm keeping those chemicals outside my water bottle and not ...
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Exo- or endothermic? Clarification required regarding a few cases
Are the following processes exothermic or endothermic?
a) When solid $KBr$ is dissolved in water, the solution gets colder.
b) Natural gas ($CH_4$) is burned in a surface.
c) When concentrated $...
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How do you calculate the total heat capacity of a reaction
I need help with this one homework question:
I am combining $100\,\text{mL}$ of $0.5~\text{M}~\ce{HCl}$ and $100~\text{mL}$ of $0.5~\text{M}~\ce{NaOH}$ to obtain $200~\text{mL}$ of $0.25~\text{M}~\...
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Intuitive explanation for enthalpy of hydration
In my chemistry course, we were discussing types of enthalpy and the enthalpy of hydration came up. My instructor defined this as
heat associated with adding water to an anhydrous salt.
However, I ...
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Diluting methanol in water: is it exothermic?
Can someone explain in simple terms why does temperature increase when mixing water with methanol? I do not have a strong background in chemistry, but I usually have to mix both liquids (sometimes ...
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Isothermal paradox(kind of)
I have recently read that for an isothermal expansion ∆u =0 which implies that work done =heat released as temperature remains constant ....but also I read that q=m×c×∆T which in this case should be ...
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Calculating entropy change of surroundings
I have seen many similar questions but have not found my answer. Why do we use the actual heat involved in the process to calculate entropy change of surrounding? The only answer I can think of is ...
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What is Enthalpy?
At school, they teach the following two formulas: $$\Delta H = -mc\Delta T$$ and $$q= mc\Delta T$$ What i am not sure is that my teacher says that q and $\Delta H$ are the same thing but to think of q ...