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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70 views

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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1answer
5k views

The Boiling or Evaporation of Diethyl Ether

When we heat water, we see bubbles appear as the boiling point approaches. The water then "boils" vigorously as it is converted from the liquid phase to a gas. I realised recently that during an ...
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Why does lead nitrate powder on heating starts turning yellow from the top rather than from the bottom?

Today while in school, I observed the thermal decomposition of lead nitrate. The peculiar thing I noticed was that the lead nitrate powder in the test tube starts turning yellow (due to the formation ...
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1answer
141 views

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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1answer
78 views

Enthalpy Change

In calculating the change of enthalpy in converting Fulminic to Isofulminic acid, would one simply take the sum of the negative enthalpies of the bonds of Isofulminic acid minus the sum of the ...
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1answer
439 views

What does "heat is evolved at standard-state conditions" mean?

When $\pu{0.539 g}$ of $\ce{Na(s)}$ reacts with excess $\ce{F2(g)}$ to form $\ce{NaF(s)}$, $\pu{13.3 kJ}$ of heat is evolved at standard-state conditions. What is the standard enthalpy of formation ($\...
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1answer
1k views

How to determine the mass of ammonium nitrate needed and enthalpy of solution?

I am trying to figure out how to determine the mass of ammonium nitrate needed to reduce the temperature of solution from $\pu{23 ^\circ C}$ (measured room temperature at start) to $\pu{3 ^\circ C}$, ...
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1answer
2k views

If aliens lived in a hydrogen (or any flammable gas) based atmosphere, would they perceive oxygen to be flammable?

Energy, fuel, and oxygen are needed for a fire to burn. In a hydrogen chamber, if there was a pipe spewing small amounts of oxygen, could you light the oxygen on fire as it began to mix with the ...
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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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2answers
772 views

Confusion in understanding temperature change in exothermic reactions

The question due to which my doubt arose $\ce{->}$ The following system is in equilibrium: $\ce{SO2Cl2 + {Heat} -> SO2 +Cl2}$ What will happen to the temperature of the system ...
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335 views

Are wrinkles\folds in paper reversible by heat, pressure or something else?

I ran into this question on Lifehacks.SE, regarding how to remove wrinkles from a crumpled piece of paper. Suggestions included ironing the paper or placing it under some heavy books for a few days. ...
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1answer
435 views

Relationship between heat and standard enthalpy for a reversible reaction

The enthalpy change for a reaction is equal to the heat absorbed at a constant pressure. My notes say that the standard enthalpy change is the heat absorbed when the reactants (in their standard ...
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Themochemistry-unknown metal [closed]

Pellets of an unknown metal were heated to 95.0 °C and then transferred to a calorimeter containing 175 g of water at 20.0 °C. The highest temperature recorded was 23.6 °C and 96.0 g of the metal were ...
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616 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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Entropy of surroundings and heat

Apparently the entropy change of a system can be found by $$\mathrm dS=\frac{\mathrm\delta q_\mathrm{rev}}T$$ I am slightly confused about this because I have seen this being used when the temperature ...
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0answers
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Is there any convenient way to warm water-based products to room temperature at home? [closed]

When it's cold outside, some household water-based products (liquid soaps, wet wipes) become cold to the touch as well. Since these products are used directly on the skin, their coldness may cause ...
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2k views

How to determine the specific heat of aluminum?

I have a question from my AP preparation book that I got wrong and do not understand the explanation: A student designs an experiment to determine the specific heat of aluminum. The student heats a ...
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1answer
108 views

Finding formula of hydrated potassium chromium(III) sulfate through experimentation

I'm in Year 13 and this is a past paper question which I don't have a mark scheme for and I'm confused on the chemistry. Hydrated potassium chromium(III) sulfate has the formula $\ce{KCr(SO4)2.xH2O}...
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1answer
2k views

Finding equilibrium temperature when two things are mixed

10 g of ice at −10 °C is added to 10 g of water at 85 °C. What is the final temperature and amount of ice left in the system? (System is kept inside an ideal insulator) This question may seem quite ...
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1answer
4k views

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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0answers
631 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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2answers
15k views

Chemical reaction that can produce lots of heat from 2-3 simple liquid ingredients?

Have an experiment I want to try out utilizing thermoelectric power and I want to generate the heat via a simple chemical reaction. Ideally I'd like to mix 2 liquids together (one being water or ...
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1answer
847 views

How can both kinetic and potential energy increase simultaneously in a open substance?

I have an open test tube containing a solid substance. In a school environment, we heat it, which increases thermal (kinetic) energy, and this heat breaks its bonds, increasing its potential energy, ...
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2answers
4k views

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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670 views

How does a diatomic molecule vibrate in response to heat?

Do you know of any applet/animation that shows how a diatomic molecule like $\ce{O2}$ or $\ce{N2}$ vibrate in response to/ to produce heat? Can it vibrate only on one axis, the one joining the two ...
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5answers
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Microwaving a glass of water, what happens?

Most of us here would already know the simplified idea behind microwaving food: Microwave radiation hits the water molecules present in food, which excites them and causes 'em to vibrate rapidly in ...
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303 views

Why is the reaction enthalpy the same as change in enthalpy for each of the reactants and products?

How come the $\Delta H$ of the reaction is the same $\Delta H$ for each of the reactants and products? For example, in an equation, the $\Delta H$ of the reaction is $244 \,\mathrm{kJ}$. When my ...
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1answer
753 views

Calculating Heat Release from Bomb calorimeter

When $0.400\ \mathrm g$ $\ce{CH4}$ is burned in excess oxygen in a bomb calorimeter that has a heat capacity of $3245\ \mathrm{J/^\circ C}$ a temperature increase of $6.795\ \mathrm{^\circ C}$ is ...
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1answer
113 views

Copper and water heat capacity concern

What mass of copper, originally at $50\ ^{\circ}\text{C}$ must be added to $1\ \mathrm{kg}$ of $10\ ^{\circ}\text{C}$ water to raise the water temperature by $10\ ^{\circ}\text{C}$? We can work out ...
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2answers
2k views

Why does hand sanitizer heat up?

While washing my hands with soap I added some hand sanitizer just because it was right there on the counter and couldn't resist mixing them... Ha! However, when I added the hand sanitizer it heated ...
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1answer
178 views

Is 70% isopropyl alcohol still inflammable after 24h?

I was wondering if Isopropyl can still produce flames after being vaporised on wood and having a day to evaporate plus rinsed with hot water afterwards? If I put heat on the wood (around 50 degree ...
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1answer
44 views

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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1answer
2k views

How is the specific heat of an alloy obtained?

I was wondering: How is the specific heat of an alloy obtained? My first attempt is to assume a thermal equilibrium between a mechanical solution and an homogeneous solution of two metals, A and B. ...
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2answers
883 views

Silicone for use in casting Bismuth

I am trying to cast bismuth, which melts at 271.4 °C. Silicone rubber seemed like a good material to use for a mold, given its flexibility and the ease with which it can be cast itself, as well as its ...
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1answer
232 views

Solving for Heat flow in Reversible Isobaric Expansion

This question was given on my Practice midterm: Calculate $q,w,\Delta U$ and $\Delta H$ for a reversile isobaric expansion from (1.00 Bar, 20.0 L) to (1.00 bar, 40.0 L) Equations used: $q_p=C_p\...
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2answers
17k views

How does sulfuric acid react to heating?

How would $\ce{H2SO4}$ react to heat? I assume that it would form toxic sulfur (di/tri)oxide, but I can't find any information on this. I'm concerned about fire hazards specifically, so assume very ...
3
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1answer
391 views

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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1answer
172 views

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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1answer
1k 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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353 views

Computational heat of reation vs. using literature values [closed]

My question is I don't understand how to explain why or what I did wrong to have such large differences between my computational heat of reaction and heat of reaction using enthalpies of formation ...
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3answers
28k views

Relation between constant-pressure and constant-volume heat capacities: Cp - Cv = nR

For an ideal gas, we have $$C_p - C_V = nR$$ where $C_p$ is heat capacity at constant pressure, $C_V$ is heat capacity at constant volume, $n$ is amount of substance, and $R=N_\mathrm A\cdot k_\...
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1answer
14k views

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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1answer
122 views

Thermochromic, fluorescent fluid

I'm a total layman in chemistry and am working on an interactive sculpture project and therefore am researching into fluids that have certain properties - long story short: we are thinking on having a ...
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1answer
177 views

Why does water have no latent heat?

When we continue to heat water at its boiling point it evaporates and some latent heat is stored in the steam formed, but when we heat ice at its melting point then why doesn't any latent heat get ...
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3answers
7k views

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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1answer
67 views

How is latent heat of vapourisation utilized in changing state?

If latent heat of vapourisation is utilized in overcoming intermolecular forces of attraction between the participle of a material then how is it still hidden there? If latent heat is used in ...
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1answer
80 views

Confusion with usage of heat capacity in Adiabatic expansion

My book says, that if a system is expanding adiabatically then $dq=0$ and $U= q+w$, so $U=w$. It also states that $$\delta U=(C_v)\cdot\delta T$$ Here $C_v$, is the molar heat capacity at constant ...
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1answer
326 views

Could compressed refrigerant be stored feasibly in residential setting?

In Vapor-compression refrigeration, a refrigerant is compressed releasing heat (typically outside a building) and then decompressed in another location, absorbing heat. A residential air conditioner ...
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1answer
469 views

How to prevent Ag2O from decomposing to Ag on Aluminum

I have silver oxide in an ink formulation. When I apply it (in small quantities) over aluminum and heat the resulting (to evaporate the solvent), the monovalent silver oxide seems to decompose to Ag. ...
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1answer
708 views

Determine volume of methane used to heat x water to x degrees?

I have 126.39 L of water. What volume of methane gas would I need to combust to heat it (at room temp, 21 degrees Celsius) to 38 degrees Celsius? How much $\ce{CO2}$ gas would be produced? I ...

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