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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56 views

Predicting the temperature of an object using the heat of its surroundings after a certain amount of time?

how would you predict what the temperature of something would be if it spends a certain amount of time exposed to heat from its surroundings? is this possible? ex. what temperature would a hot ...
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87 views

How do you stop a Pharoah's Serpent reaction?

I am a novelist and working on a book. I have been searching google for an answer to the above question. How does one stop a Pharoah's Serpent reaction? Thanks!
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Calculate Heat of Atomisation [closed]

What is heat of atomisation of P4O6(s) Given heat of sublimation of P4O6 is x kJ/mol & P–O bond energy is y kJ/mol. What is heat of atomisation of P4O6(s) Given heat of sublimation of P4O6 is x ...
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85 views

Can air inside a high temperature (1300C) Kiln cause an explosion?

I saw many kiln designs that lack an opening for hot\pressurized air to come out , or any pressure valve. But when air is heated to such a high temperature (1300C) inside a closed chamber (the kiln), ...
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2answers
465 views

Sign of work done by the system in first law of thermodynamics equation

In the equation, $\Delta E = q - W$, according to my book, $W$ is positive when it is done by the system and negative when it is done on the system. But in this problem: $\pu{3600 kJ}$ heat is ...
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1answer
366 views

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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1answer
545 views

Is there any difference between "autoignition temperature" and "ignition temperature"? [closed]

Is there any difference between the "autoignition temperature" and the "ignition temperature" of a substance?
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408 views

Fried potatoes absorbing oil [closed]

Suppose we bring a pan and put in it some oil and turn on the heat, before the oil could get very hot and nearly boiling, we put on the potatoes that start frying. Someone told me that if the ...
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1answer
166 views

What would happen if you heat volatile/flammable material in a vacuum? [closed]

Fire is an oxidizing chemical reaction, in the simplest sense it needs oxygen and fuel to burn in order to stay alight. But what reaction would you observe from a flammable substance like gasoline or ...
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1answer
102 views

Can heat capacity at constant volume for a gas decrease as temperature increases? [closed]

I found a function for the $C_V$ of a gas which is being heated under constant volume,but the function shows that the $C_V$ is decreasing. I was wondering if this is possible for any gas since I know ...
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slow down ice melting in water

Having to separate freshwater crabs for commercial fisherman while on the boat, we dump the crabs in ice water, as crabs aren't as aggressive and bite less when cold. There's only so much room on the ...
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185 views

Why don't we consider VΔP when we define Q?

We only define $Q = \Delta U + W_\text{exp}$ (expansion work = $-P\Delta V$). If heat can cause $\Delta U$ and work, why work is defined only as expansion work in the first place where there are other ...
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Thermodynamics energy balance question help

I made the following attempt to solve this question.However I don't know how to find final pressure.I don't know how to find final temperature for both sides.Can you give me a hint?
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Enthalpy of formaton [closed]

today I was doing a set of HW problems regarding enthalpy and stumble upon one problem that I found confusing.It was the standard enthalpy of formation for CaCO3 is -1207.6 kJ mol when 30.7 g of ...
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267 views

Does specific heat capacity of the container have an effect on the exactitude of a calorimetre?

I'm doing a lab on what is the best material for a calorimetre. I chose glass, aluminum, styrofoam cup, paper/cardboard cup and a plastic cup. I've found that the cardboard cup was the best followed ...
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1answer
395 views

Why might copper have a lower heat capacity than lithium according to the Shomate Equation?

I've learned that according to Condensed phase thermochemistry data, according to NIST, the functions of heat capacity, enthalpy, and entropy can be predicted by the Shomate Equation: $$\begin{align} ...
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239 views

Can the change in the entropy of the surroundings always be obtained by dividing heat transferred by the temperature at which the transfer occurs?

Consider $\pu{1 mol}$ of an ideal monoatomic gas going through reversible isochoric heating from $\pu{100 K}$ to $\pu{1000 K}$. Calculate $\Delta S_\pu{sys}, \Delta S_\pu{surr}.$ $$\Delta S_\pu{sys} =...
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Why 'Enthalpy change' (Delta H) is equal to 'Heat transfer at constant pressure' (Qp)? [closed]

Why 'Enthalpy change' (∆H) is equal to 'Heat transfer at constant pressure' (Qp)? ∆H = ∆U + ∆pV, here only expansion work done by the sustem is added. If non expansion work is done on the system then ...
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1answer
128 views

When boiling a liquid, how vapour pressure and ambient pressure get equal? [duplicate]

When boiling a liquid, how vapour pressure and ambient pressure get equal? As vapour pressure will increase, it will lead to increase in ambient pressure also. let, Initially there would be some ...
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1answer
50 views

Heat capacity determination

Since heat capacities are determined in a calorimeter taking advantage of the known heat capacity of water, how was the heat capacity of water originally determined?
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260 views

Thermochemistry - zero heat energy

We were just wondering in our chemistry class: is there any reaction which is neither exothermic nor endothermic?
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36 views

Won't gas thermometers break on using fixed volume of gas?

From the ideal gas equation, PV is proportional to T. Now if V is kept constant, we'll get Gay-Lussac's law. Now my question is: According to observations, we know that substances undergo a change ...
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1answer
4k views

Am I Using the Correct Number of Significant Figures (Heat Problem)?

The question is: A patient arrives in the emergency room with a burn caused by steam. Calculate the heat, in kilocalories, that is released when $\pu{18.0 g}$ of steam at $\pu{100 °C}$ hits the ...
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549 views

Calculate work done by burning benzoic acid exposed to the free air

I'm self-studying and can't solve this problem in Ball's Physical Chemistry. Now, the errata shows that the answer in the book is not correct; still, I can not make sense of it. $(2.55)$ Benzoic acid,...
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How to know whether to add latent heat when calculating final temperature?

From the examples in my textbook, it is usually very easy to see whether you need to account for the latent heat when calculating the final temperature. For example, if you add 2 x 13 gram ice blocks ...
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Difference between Enthalpy and Heat transferred in a reaction?

We know at const pressure change in enthalpy is change in internal energy plus work done. Here by taking enthalpy as heat i can easily think the situation in mind that heat absorbed is due to the two ...
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1k views

ΔH of reversible expansion of ideal gas

Since its isothermal, $\delta U$ is zero. But enthalpy change $\delta H$ is $\delta U + \delta n(\text{gaseous})RT$ or $\delta H = \delta U + \delta (pV)$. For reversible isothermal expansion of ...
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Calculating the heat of formation of propane given its enthalpy of combustion

Given the equation $\ce{C3H8 + 5O2 -> 3CO2 + 4H2O}$ and that enthalpies of formation for $\ce{H2O (l)}$ is $\pu{-285.3 kJ/mol}$ and $\ce{CO2 (g)}$ is $\pu{-393.5 kJ/mol}$, and the enthalpy of ...
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128 views

Finding $c$ with Dulong-Petit law on non-molecular substance

The Wikipedia article states the Dulong-Petit law as follows: $$c=\frac{3R}M$$ $c$ is specific heat capacity $[\mathrm{\frac J{kg\; K}}]$ and $R$ the gas constant. $M$ is the molar mass in [g/mole], ...
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918 views

Which cup of tea cools down more quickly?

There are 2 cups (both cups are identical) of tea which are served at the same temperature. Assume that the walls of the cup to be non-heat conducting. Which cup of tea cools down faster, a full-...
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122 views

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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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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When heat is increased, does water move upward in a straw due to increased capillary action or increased pressure?

I left a water bottle with an internal straw in my car throughout a long, hot day. When I opened the bottle at the end of the day, water immediately splashed out from the straw. This made me wonder if ...
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18k views

Cp-Cv For a gas following Van Der Waal equation of state [closed]

How do you derive the relation $$C_p-C_v= R\left(1 + \frac{2a}{RTV}\right)$$ for a gas obeying van der Waals equation of state? Any leads?
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Heat capacity of mixtures is higher than their pure contituents?

I'm currently studying the effects of how changing mixed-refrigerant compositions effects their heat capacity. Surprisingly, my data suggests that some combinations of mixed-refrigerants have heat ...
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Is there a cheap, safe liquid that evaporates EXOthermically around room temperature?

The heating and AC system in the building where I occasionally work, works like this (basically a thermostat): The administrators set some temperature that is maintained automatically. Say, in the ...
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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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952 views

Why would the specific heat capacity of water be used as the specific heat capacity of zinc sulfate?

I could not find the specific heat capacity of zinc sulfate and saw that people use water's heat capacity instead. Why is that?
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256 views

How do scientist obtain the value of enthalpy of formation? [closed]

Do they do it experimentally or do/can they use bond enthalpy to figure it out? For example $\ce{C2H4 + H2 -> C2H6}$. The enthalpy of formation, $\Delta_fH$ of formation for the product is listed ...
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How does boiling water affect its hardness?

Does boiling water reduce its hardness, or on the contrary, increase it? It seems there are ambivalent phenomena at play here: boiling will evaporate pure water, thus increasing the concentration of ...
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364 views

How to calculate the latent heat when there is a boiling temperature range?

I have a DME (dimethyl ether)- methanol - water mixture with the mol fraction composition: DME 0.4295, methanol 0.1353, water 0.4351. This mixture has a boiling temperature range: dew point 141.6 °C ...
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Formation: So much heat, where does it all go?

I was comparing heat of formation numbers with specific heat values, and the numbers look really weird. Take a typical example like magnesium fluoride. Its $\Delta H$ is -1124 kJ/mol and its heat ...
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3k views

How is work converted to heat?

My book says work can be converted into heat but I want to know how work affects kinetic energy of molecules which, when transferred, is called heat?
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How to calculate the specific heat of ethanol?

I am currently stuck with this question. Can somebody please help me with this? 100 g of water was heated from $\pu{15 °C}$ to $\pu{70 °C}$ by burning $\pu{20 g}$ of ethanol. How much energy per ...
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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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Can thermite be lit while mixed into butane? If not is there a flammable liquid that would work?

I want to create a thermite flamethrower to melt snow since I live in New England and since I am an asthmatic I struggle to shovel and it would be cool, so do you have any idea as to what liquid ...
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Heating a mixture of methanol and water?

I have a mixture methanol and water, at 25°C, and I want to take it to 250°C. I'll use two heat exchangers: one for taking the mixture from a liquid state (25°C) to a vapor state (X°C), and the second ...
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673 views

Can Pyrex laboratory grade glassware be heated on a stovetop?

I don't have access to a hot plate, I was wondering if Pyrex glass can be safely heated on a stove top. It isn't an open flame, it's a radiant stove top with an electric coil underneath a smooth ...
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588 views

How do I calculate the standard enthalpy of formation for liquid ethanethiol? Do I use Hess's law? [closed]

Calculate a value for the standard enthalpy of formation for liquid ethanethiol, $\ce{C2H5SH}$. Use the equation given below and enthalpy of combustion data from the following table. Just assume ...
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310 views

Do processes involving synthesis need heat?

I came across a textbook that stated a combination process that required heat. There was no explanation whether it was a prerequisite for a combination process to have heat or it was just an example ...

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