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 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)...
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1answer
24 views

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 ...
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1answer
23 views

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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1answer
77 views

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, $...
3
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1answer
78 views

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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2answers
126 views

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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1answer
36 views

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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0answers
38 views

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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29 views

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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0answers
13 views

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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0answers
28 views

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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1answer
70 views

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. ...
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2answers
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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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1answer
57 views

Heat of formation of aqueous H⁺

In my book it is given that by convention heat of formation of aqueous $\ce{H+}$ is taken to be zero. Heat of formation is energy released or absorbed when 1 mole of a compound is formed from its ...
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4answers
95 views

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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4answers
135 views

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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2answers
89 views

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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1answer
131 views

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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2answers
51 views

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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2answers
78 views

Heat transfer through layered wall

An electrical heater is placed between two layers of insulation. The three layers (the heater and the two layers of insulation) have the same thickness. The figure below shows different temperature ...
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0answers
52 views

Adiabatic flame temperature of a blast furnace gas

Calculate the adiabatic flame temperature of combustion of a blast furnace gas analyzing $25\%$ $\ce{CO}$, $10\%$ $\ce{CO2}$, and rest nitrogen. Use theoretical amount of preheated air at $\pu{1000 °C}...
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1answer
91 views

Determine surface area of heat exchange tube

A heat exchanger is used to cool down a stream of $\pu{20 kg s-1}$ of water from $\pu{80 °C}$ to $\pu{60 °C}$. The cooling water enters at a rate of $\pu{12 kg s-1}$ and $\ce{20 °C}$. The overall heat ...
3
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1answer
48 views

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 ...
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2answers
402 views

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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2answers
78 views

Does dissolving something in water change the specific heat of the solution?

I’m a little confused on this topic. If I have a solid that I dissolve in water and that undergoes an exothermic reaction, can I assume that the specific heat $c$ of the solution instantaneously after ...
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1answer
95 views

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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47 views

Heat of formation method

For enthalpy calculations why is it that in some cases the "heat of formation method" is used? I know that $ΔH_f$ represents the heat required to form the compound at standard temperature and pressure ...
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2answers
42 views

Is paper aging(oxidation) and paper burning(rapid oxidation) the same thing?

I woke up today with a question of what is fire; looked up the definition and the first response was that fire was rapid oxidation. I was curious what the difference was between rapid oxidation and ...
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1answer
75 views

Is it safe to heat fluorite (CaF2) to 140 °C?

For the manufacture of the optical system, we need to heat the fluorite ($\ce{CaF2}$) lenses to $\pu{140 °C}$. Is it possible: for some poisonous gas to be emitted? ($\ce{F2, HF}$ or other) for ...
3
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1answer
65 views

Why do we use Δ to mean heating?

To express heating, we usually use $\Delta$ over reaction arrows like \begin{align} \ce{CaCO3 ->[\Delta] CaO +O2}. \end{align} Why do we use $\Delta$ to mean heating during chemical reactions? I ...
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1answer
790 views

Why does the temperature remain constant during freezing?

I know it's the most silly question one could ever ask but why is that so? I am aware of what latent heat means and I also know it has something to do with freezing too. Say I have with me, a mug of ...
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1answer
547 views

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 14 cal/gC and helium has a specific heat of 5 cal/gC, which would be much ...
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2answers
74 views

Intuituve reason for the constant of proportionality 2/3 in pv=nRT=(2/3)U

Why is there a $\frac23$ term? I fully understand that it makes sense for pressure to be the volume weighted average kinetic energy. And the equation above shows that this is so (for an ideal gas). I ...
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1answer
90 views

Calorific value of a gas in combustion

The Wikipedia article on heat of combustion says: The calorific value [...] may be expressed with the quantities: energy/mole of fuel energy/mass of fuel energy/volume of the fuel ...
2
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1answer
450 views

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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1answer
69 views

Heat generation in exothermic reactions [duplicate]

Im thinking specifically of N2 + 3 H2 ⇌ 2 NH3. Its an exothermic reaction, therefore heat is generated. Im trying to understand how Chateliers principle interacts with this reaction. I understand that ...
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1answer
117 views

Heat transfer problem

For this problem, I'm wondering if the thermos should be involved in the heat transfer because right we have an equation in calorimetry: $q_\text{warm} =-(q_\text{cold} + q_\text{cal})$ A 125 g ...
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1answer
41 views

Specific heat problems [closed]

I am in need of help for my understanding in specific heat capacity. To be honest, I understand the lesson effectively, However, just a few days ago, I've encountered two similar yet different-in-...
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0answers
76 views

distillation of aqueous CAN solution for the purpose of a reversible and strong endothermic reaction in cool packs

I know calcium ammonium nitrate (CAN) is used for cold packs. By bending a small metal plate the salt gets dissolved in water (separated pack) and this process is endothermic. I would like to heat ...
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1answer
1k views

Why would a ~1 cm thick layer of argon be a significantly poorer conductor of heat than air?

In yesterday's new Periodic Video, Argon (new) - Periodic Table of Videos, after about 07 min 00 sec, Sir Martyn Poliakoff says: The final, and I have to admit perhaps slightly boring application ...
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1answer
84 views

Flexible & thermally conductive materials? [closed]

Quick question: Are there any common or easily obtainable materials that are thermal conductors, but also flexible? By flexible, I mean along the lines of a plastic bag, with similar or greater ...
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0answers
241 views

What is the specific heat and latent heat of an ethanol-water mixture?

How do I find the specific heat and latent heat of ethanol-water mixture? Let’s say the mole fraction of water is 0.3 and ethanol is 0.7. I am working on a project and needed values for these and ...
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1answer
129 views

Heat of Combustion

Methanol ($\ce{CH3OH}$) is regarded by many chemists as a possible liquid fuel for the future. The combustion of methanol occurs according to the equation: $$\ce{2CH3OH(g) + 3O2(g) -> 2CO2(g) +...
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2answers
554 views

Why do aluminum and air have low specific heats?

According to Wikipedia, ...specific heat capacity is a function of the structure of the substance itself. In particular, it depends on the number of degrees of freedom that are available to the ...
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3answers
2k views

Why are calorimeters often made of materials with low specific heats?

When building calorimeters, a material with a low specific heat is often used (such as Styrofoam, aluminum, etc.). However, why would a material with a low specific heat be preferred? My thought ...
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1answer
47 views

Where can I find the total enthalpy and heat of dissolution in water of a given components?

I don't really have a background in chemistry but I'm actually studying in aerospace engineering, sorry if this question may seem trivial. I am interested in the decomposition process of the hydrogen ...
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1answer
44 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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1answer
79 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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543 views

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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1answer
45 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), ...