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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How can decreasing in temperature indicate an endothermic reaction?
I’m really wondering how can decreasing the temperature refer to an endothermic reaction.
I faced this when I was calculating the heat of a reaction Q in a constant-pressure calorimeter.
What I ...
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Why does ice water get colder when salt is added?
It is well known that when you add salt to ice, the ice not only melts but will actually get colder. From chemistry books, I've learned that salt will lower the freezing point of water. But I’m a ...
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What exactly is temperature?
I've read at many places that temperature is the average kinetic energy of particles present in an object. I just don't intuitively get how kinetic energy is connected with temperature. And how is ...
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Heats of combustion and stability of rings
Which isomer would have the largest heat of combustion?
A) Propylcyclopropane
B) Ethylcyclobutane
C) Methylcyclopentane
D) Cyclohexane
E) Since they are all isomers, all would have the same heat of ...
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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 you heat water with additives?
I have been curious about this question for a while. If you want to warm up a large amount of water, is it feasible to do this by adding a substance that has an exothermic reaction with the water? ...
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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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Which materials/compounds expand in response to cold temperatures?
Which materials or compounds expand in response to cold temperatures?
This material or compound should expand at a slow (yet constant rate), from 0 to about 20 months when in the temperature range ...
natasa
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How much heat is needed to break CO2 down to CO?
I have found that because the oxygen is double bonded to carbon, it takes about $\mathrm{1500\ ^\circ C}$ to break it down from $\ce{CO2}$ to $\ce{C}$ and $\ce{O}$. But, I am curious, would it take ...
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Why total heat of hydrogenation of 1,3-cyclohexadiene is more than that of benzene?
I'm told that heat of hydrogenation (HOH) is directly proportional to number of π bonds and inversely proportional to stability. So, is the aromaticity responsible for this?
Also, what is the general ...
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Why does milk overflow when boiled?
I was wondering that like whenever I boil milk I just have to keep standing in front of it to make sure that I don't waste any milk but then I was wondering like Why does it even overflow ? In case of ...
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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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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 ...
user35894
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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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Minimum amount of water in pressure cooker
When cooking I would like to know the minimum amount of water I can add to my 6.2 L pressure cooker, worst case, so without any food. At second ring cooking the pressure is 0.8 bar.
I assume I need ...
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Why is the specific heat of water high?
How is the specific heat of water so high?
I was reading the hyperphysics article on it but could not understand it properly.
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What is the difference between enthalpy (H) and heat (q)?
It seems that in some cases it's the same (that is, $\Delta Q_p=\Delta H$) yet in others they differ.
For example,
\begin{align}
\ce{2H2(g) + O2(g) &->2H2O(l)} & \Delta H &= -572~\...
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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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Why substitution and elimination reactions are favored respectively at lower and higher temperature?
I read about the competition between nucleophilic substitution and nucleophilic elimination depending on temperature here. Though the webpage clearly says higher temperature favors elimination while ...
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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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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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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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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 ...
user19300
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How can I light a fire in this case?
Is there any gas that contains oxygen so that it doesn't require oxygen from the environment in order to burn?
What I am trying to do is use LPG gas, which is fed through a pipe to a burner that is ...
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What properties of carbon dioxide make it a greenhouse gas?
Why is it that heat from the Earth reflects back off carbon dioxide and other greenhouse gases but not gases like nitrogen or oxygen?
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Why does diamond conduct heat better than graphite?
Our teachers made us accept (without any explanation) that diamond conducts heat better than graphite. What is the reason behind this (alleged) fact?
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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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How can 30 ml of water be heated in less than 10 seconds?
How is it possible to heat a tiny amount (30 ml)[1] of water to a high enough temperature to make a coffee, in less than 10 seconds and possibly instantly?
Most heaters that I know of heat water ...
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Burns from boiling water and steam
Why is a burn to the skin caused by steam more serious than a burn caused by the same amount of boiling water at the same temperature?
The temperature is the same, which implies that the kinetic ...
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How is enthalpy change equal to heat supplied at constant volume?
We know that:
$$\begin{align}
H &= U + pV \\
\Delta H &= \Delta U + \Delta (pV)
\end{align}$$
Now,
If $p$ is constant,
$$\begin{align}
\Delta H &= \Delta U + p\Delta V \\
&= q_p + ...
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Can single molecules of C and O2 react in isolation, and if so how will momentum be conserved?
I am trying to figure out how is it possible to reconcile the reality of exothermic reactions, which means that kinetic energy is transferred to (heats) the surrounding matter, with the principle of ...
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What happens if I make a hole in a container with superheated water?
Superheated water is achieved by heating water above 100 degree Celsius under high pressure.
Now, suppose the temperature at which the water is getting heated is around 250 Celsius and sufficient ...
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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 reactions).
Consider ...
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Do I understand why heat capacity is called 'heat *capacity*'?
The notion of heat capacity seemed a little odd to me. I thought that the word 'capacity' could be throwing me off. Do I understand the notion correctly?
I take the word 'capacity' to express, ...
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Why does a substance with an endothermic heat of solution dissolve?
How does a substance with an endothermic heat of solution dissolve?
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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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Can water be ignited in an ozone atmosphere?
According to my calculations, the reaction $\ce{H2O + O3 -> H2O2 + O2}$ should be favourable under standard conditions. However, I am told that the reaction is probably very slow in solution since ...
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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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How much heat is required to dehydrate a hydrate?
If I have a hydrate, such as copper (II) sulfate pentahydrate, $\ce{CuSO_4 \cdot 5H_2O}$, what is the amount of heat to required to dehydrate it? I assume that it is equal to or greater than 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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Is it possible to make broad spectrum light absorbing paint?
Is there such a paint / pigment that absorbs most wavelengths of light (beyond the visible light range) that can be used for solar heat generating applications? If not, would it be possible to make ...
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Meaning of red heat
I have two reactions below.
What is the difference between red heat and normal heat? Is it related to iron as a catalyst when it is red hot?
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Temperature dependence of reaction enthalpy
Estimate $\Delta_\mathrm{c}H^\circ(500\mathrm{~K})$ for methane by using the data given on the temperature dependence of heat capacities.
$$\ce{CH4(g) + 2 O2(g) -> CO2(g) + 2H2O(g)}$$
My ...
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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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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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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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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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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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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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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 ...
user36543