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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Heat transfer to an ideal gas [closed]
In thermodynamics, why is the heat that is transferred to an ideal gas considered as work that was done on the system for an isothermal process?
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Understanding the term 'heat of hydrogenation'
From Chemistry Libretexts:
Heat of hydrogenation (symbol: $ΔH_\mathrm{hydro}$) of an alkene is the standard enthalpy of catalytic hydrogenation of an alkene.
Does the heat of hydrogenation include ...
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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 ...
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Strong exothermic mixing of two 'safe' liquids
I have read (thanks to Stack Exchange) that mixing water and sulfuric acid is exothermic, as is NaOH and HCl.
Are there two 'safe' liquids that can be mixed and produce anywhere near the same amount ...
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Regarding the infinitesimal form of the First Law of Thermodynamics
First Law of Thermodynamics is expressed as[1]
The internal energy of an isolated system is constant.
If $w$ denotes the work done on a system, $q$ for the energy transferred as heat to the system,...
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Can dissipative work be circumscribed as irreversible heat transfer
My question refers to an article I read yesterday in which the author states that for the calculation of the entropy change for a process (in that case friction, during an irreversible adiabatic gas ...
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Acid-Temperature coagulation of milk
I was making coffee with a cup of boiling milk which was 2 days old. I used instant coffee powder and some sugar for the making of it. Tried to make a very hot coffee but usually prefer medium hotness....
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Does calcium nitrate decahydrate dehydrate or decompose upon heating to 100 degrees Celsius? [closed]
Consider a sample of $\ce{Ca(NO3)2.10H2O}$. To remove water, I need to heat it to $\pu{100 ^\circ C},$ but will this high temperature decompose it or will I get the anhydrous salt?
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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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Will the temperature of a faucet actually be lower than the countertop or will it only feel cooler due to specific heat?
Due to specific heat capacity of metals, they feel cooler because they don't retain as well as other materials. But is their temperature actually lower if it could be measured?
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Clarification required on whether to use $C_v$ or $C_p$ in this question on finding entropy change
$1 \text{ mol}$ of an ideal monoatomic gas at $300 \text{ K}$ is subjected to a reversible isentropic compression process until final temperature reaches $600 \text{ K}$. If initial pressure is $1 \...
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Steam rises when the heat supply stops
When water boils and you suddenly shut the heat off, a lot of steam arises from it just after you shut the heat off. Why this happens, I thought that maybe water condenzes very fast in small droplets ...
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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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Hess's Law and ΔH
Target equation: $\ce{Mg(s) + 1/2 O2 -> MgO(s)}$
$$
\begin{align}
\ce{MgO(s) + 2 HCl(aq) &-> MgCl2(aq) + H2O(l)} &\quad ΔH &= \pu{-1300 kJ} \tag{1}\\
\ce{Mg(s) + 2 HCl(aq) &-&...
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Why could it be assumed that the standard enthalpy change is independent of temperature down to 25 °C?
For the reversible reaction of pyruvic acid to 2,2-dihydroxypropanoic acid, we calculated enthalpy using NMR and extrapolated from area (integration) and peaks etc.
We then plotted $\ln K$ vs $1/T.$ ...
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Why does ice get colder when you add salt? [duplicate]
I know that when you put salt on ice it may turn to a slush and it does feel cold. What is the reason for this?
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Deciding the order of heat of combustion of isomeric alkanes
I'm asked which one of the alkane has the lowest heat of combustion (note: the question says heat, not enthalpy) and according to the answers, the right one is d.
I'm trying to understand why d ...
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Can the human body withstand the heat from setting plaster?
There was an incident a couple of years ago where a teenage girl during an art lessen got her hands stuck in a bucket with plaster. As the plaster set, the heat from the chemical process caused her ...
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Why are IUPAC's definitions of exo- and endothermic disconnected from the direction of heat flow?
I'm wondering if anyone can provide a rationale for IUPAC's definitions of exothermic and endothermic since they disconnect these terms from the direction of heat flow.
Specifically, here are IUPAC's ...
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Enthalpy and heat relationship
They say that enthalpy of reaction is the heat when at constant temperature and pressure. So if enthalpy is
$$\mathrm dH = \mathrm dU + p\,\mathrm dV = T\,\mathrm dS - p\,\mathrm dV + p\,\mathrm dV + ...
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Why is the product of the reaction "Bi + O2" Bi2O3 instead of Bi2O5?
I am stuck on a homework question that states:
A piece of solid bismuth is heated strongly in oxygen.
The answer key states the answer as $\ce{Bi + O2 → Bi2O3}$. However, it is to my understanding ...
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Why does boiled water have a different taste as compared to cool water? [duplicate]
I have noticed it frequently and decided to check with some of my peers and friends about this and they too have felt such a thing.
The taste comparison occurs after the boiled water is cooled down to ...
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How to derive this temperature-pressure-specific volume relationship?
(for isentropic, adiabatic, ideal gas flow)
$$\frac{T_x}{T_y} = \left(\frac{p_x}{p_y}\right)^{\frac{(\gamma-1)}{\gamma}} = \left(\frac{V_y}{V_x}\right)^{\gamma-1}$$ where $V$ is the specific volume, $...
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Is it safe to boil water in a foil pan on an electric burner?
Is it safe to boil water in a foil pan on an electric burner?
Can the metal leach into the water?
I've heard some reports recently about avoiding aluminum foil due to it leaching into food.
Photos ...
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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 ...
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How does the energy released during a bond formation typically manifest itself on atomic level?
I've been reading about how energy is released when new chemical bonds are formed but it's hard to find info on how that typically manifests itself (besides that it's via heat). I read somewhere that ...
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Could Calcium Oxide be made from CaCO3 in a bonfire?
I have some chalk and I need to turn it into CaO. Would a big bonfire be hot enough to make it? If anyone has personal experience with this reaction please share, whether succesful or not
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Heating of cyclic dicarboxylic acid [closed]
How do we predict the products formed when we heat cyclic dicarboxylic acids? I know that in case of aliphatic dicarboxylic acids we apply Blanc's rule and predict the product formed based on the ...
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How hot will a carbon electrode get in an electrolysis setup?
For the electrolysis of sulfuric acid, I plan to use carbon graphite electrodes at voltages up to 6 V. I would like to know if my carbon electrodes would get considerably hot or warm (45 °C or higher)....
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Exothermic: enthalpy or heat?
I am used to thinking of exothermic reactions as being defined as having negative $ΔH.$ However, I also am used to hearing/thinking of exothermic reactions as "releasing heat".
Since change in ...
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Why doesn't beryllium, an elemental solid, obey Dulong and Petit's law?
Beryllium has a molar heat capacity of $\pu{17.7 J mol-1 K-1},$ which is quite far from the $\pu{25 J mol-1 K-1}$ as predicted by Dulong and Petit's law. What is the reason for this discrepancy?
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How to get the efficiency of a heat engine which undergoes an elliptical cycle?
An ideal diatomic gas undergoes an elliptic cyclic process characterized by the following points in a $PV$ diagram:
$$(3/2P_1, V1)$$
$$(2P_1, (V1+V2)/2)$$
$$(3/2P_1, V2)$$
$$(P_1, (V1+V2)/2)$$
A ...
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How would a temperature profile in wall change if the rate of heat transfer increases
Given the system below, how would the temperature profile in the wall change if the heat transfer in Fluid II was very fast?
If the heat transfer in Fluid II is very fast, then the T-profile for $\ce{...
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Prolonging the exothermic reaction between calcium oxide and water
Is it possible to generate 10-minutes of heat using very small amounts of CaO and water? This is an exothermic reaction.
I've done this experiment at home, but it is very short-lived. I'm trying to ...
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Negative Molar Specific Heat of a Gas
It is known that the specific heat of a gas is process dependent. So it must be theoretically possible to have a negative value for a gas according to the following equation (for polytropic process, $...
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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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Energy balance in battery thermodynamics
I am trying to understand the derivation of a general energy balance in battery thermodynamics. The following relation is frequently found to determine the heat generation of a battery:
$\dot{Q} = \...
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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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Why mixing water with ethanol produces heat energy? [closed]
Sorry if I'm asking something stupid but I'm trying to understand where this energy gets from. As far as I could find, it is not a reaction as both chemicals left unchanged, so it might have something ...
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Calculate the energy in the form of heat (in kJ) required to convert 325 grams of liquid water at 20.0 °C to steam at 115 °C
Calculate the energy in the form of heat (in kJ) required to convert 325 g of liquid water at 20.0 °C to steam at 115 °C. Assume that no energy in the form of heat is transferred to the environment. (...
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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
...
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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}+ ...
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Derive expression for heat flow from oil bath to metal sphere
A spherical ball of iron is put into a hot bath of oil. The iron ball is initially at a low temperature and heat transfer from the oil to the iron will increase the temperature of the iron ball.
Use ...
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When a candle burns, why does the top of wick glow if bottom of flame is hottest?
Totally an elementary question.
Staring at a candle, it appears that the bottom of the wick is dark whereas the top glows. However the bottom of the flame (the blue) is the hottest.
Is the reason ...
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Heat of formation of aqueous H⁺
Heat of formation of aqueous $\ce{H+}$ is taken to be zero, by convention. Heat of formation is energy released or absorbed when 1 mole of a compound is formed from its elements in their standard ...
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How does the room gets heated by leaving a fridge open?
Question:
If the door of the refrigerator is kept open, the room in which the refrigerator is kept:
gets cooled
gets heated
neither gets cooled nor gets heated
gets cooled or heated ...
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Is heat just a change in temperature?
According to my chemistry textbook, heat is defined as "Energy that is exchanged because of a difference in temperature or a change in phase." My textbook also says, "Heat is a form of energy. ...
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Find out of the friend is getting a good deal [closed]
I have a strange chemistry question that I've never came across before, and I have no idea about how to solve it.
Your friend comes across a good deal to purchase a gold ring. She asks you for ...
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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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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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