Questions relating to heat and its relation to other forms of energy in chemistry.

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Entropy calculation (see description)

What is the entropy change when 1.00 mol of ideal gas that raises reversibly from 10 °C to 50 °C at constant pressure, constant volume, assuming the heat capacity is independent from temperature? ...
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How will liquid nitrogen behave in space?

On earth, Nitrogen exists mainly as a gas. Under a lot of pressure but what about in space ? Will it behave just like that only or there will be any difference ?
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37 views

Is helium-4 a liquid at zero temperature and zero pressure?

As far as I know, for all substances other than helium, if you extrapolate the solid-gas line on the phase diagram, it passes through the origin. That is, no matter how low the temperature is, you can ...
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1answer
37 views

Heat and water absorption by calcium chloride

Can calcium chloride be effectively used as a desiccant to absorb both heat and moisture?
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1answer
121 views

Vaporized sodium hydroxide?

Some time ago, I was making a $\ce{NaOH}$ solution. The solution I had made was much too concentrated, and the heat released in the dissolution of the ions caused the water to begin steaming. ...
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1answer
29 views

Equations for internal energy and their relevance to the derivation of the equation for entropy for perfect gases

My lecture handout proves derives an expression for entropy thus: For a perfect gas $U=U(T)$ (i.e. is not dependent on volume; only temperature). Therefore, $(\frac{\partial U}{\partial V})_T=0$ ...
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1answer
47 views

Is hot air or hot water more effective at melting a frozen pipe?

This question is related to specific heat, and I thought I understood it but I've managed to confuse myself. My initial reasoning was that since in both cases, the pipe is the same, the amount of ...
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64 views

What is the origin of the maximum in rotational heat capacity?

The graph of rotational heat capacity above shows a small maximum before approaching the equipartition value. What is the origin/physical explanation of this maximum?
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46 views

In order to solve for this equation for heat capacity, do I need to treat it as a system of equations?

For a lab, we took the temperature of 15ml of tap water, $q_{cool}$, then added 20ml of tap water warmed to 80 degrees Celsius, $q_{warm}$. We recorded a baseline temperature of 24.8, a temperature ...
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1answer
55 views

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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1answer
33 views

Hess' Law contact process question

In the contact process, the commercial process of producing $\ce{H2SO4}$, several reactions occur before the final product is produced: $\ce{S8_{(s)} +8O2_{(g)} -> 8SO2_{(g)}}~~~~~~~~~~\Delta ...
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2answers
46 views

Predicting melting points of substances based on their molecular/atomic structure

Wouldn't it be great to be able to predict the melting point of a metal based on the atomic number and not by looking in some table for the value that was measured experimentally by someone else? Or ...
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1answer
27 views

Why does raising the temperature affect the mass of dissolved solute? [closed]

Consider a solution of $\ce{KOH}$ which is in equilibrium with undissolved $\ce{KOH}$ at $25\ \mathrm{^\circ C}$. After raising the temperature to $50\ \mathrm{^\circ C}$, the mass of undissolved ...
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28 views

Entropy change in an adiabatic expansion

The following is a question on a problem sheet that I have been given; I don't know what to do: "One mole of ideal gas initially at a pressure of 1 atmosphere and T = 298 K, is expanded into a ...
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1answer
27 views

Is there more than one equation for Delta T(reaction)?

So, I have to find the $\Delta T_{\mathrm{reaction}}$ of a solution for my lab report. Earlier in the lab, it gave the equation as $\Delta ...
10
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1answer
458 views

Why can't helium be solidified at 'ordinary' pressures?

According to the UC Davis ChemWiki Chemistry of Helium, helium has a comparatively unusual property, specifically: Helium is the only element that cannot be solidified by lowering the temperature ...
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19 views

Are there any (liquid) chemicals that experience rapid, extensive, and controllable volume changes in reaction to heat?

The larger purpose of this question is the engineering of liquid filled sacs that change their volume according to heat. They'd need to have diverse ranges of volume, at least a factor of ten (a 10 ml ...
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2answers
56 views

Dependence of change in entropy on temperature

The thermodynamic definition of entropy is expressed as $$dS = \frac{dq_{rev}}{T}$$ I understand that it depends on amount of heat transferred because heat transfer can be understood as the degree of ...
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1answer
31 views

If for a chemical reaction the standard gibbs free energy is negative then :

If the standard gibbs free energy for a reaction is negative then the forward reaction will take place and the reaction will not be reversible. Is it true ? I have a problem understanding what is ...
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1answer
26 views

50-90'C color changing chemical to use as warning marker for hot electronics?

I am testing electronics with many potentially unstable contacts, and I wish to monitor if they rise above 50 to 90 degrees Celsius, i.e. using carbon paper that would darken progressively from 50 to ...
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1answer
29 views

Which of these compounds does not liberate heat when water is added to it?

Which of these compounds does not liberate heat when water is added to it: $\ce{KNO_3}$, $\ce{NaOH}$, $\ce{CaO}$, $\ce{H_2SO_4}$, $\ce{Na}$. I know from experience that dropping sodium tablets into ...
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2answers
49 views

If the temperature of a solution decreases, what is the sign of the enthalpy change?

Here is what seems to be a straightforward question: you dissolve some ammonium chloride in water at $25\ \mathrm{^\circ C}$, lowering the temperature of the solution. Is the change in enthalpy for ...
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1answer
147 views

Thermodynamics and Coffee

Heyo, I'm sure you all know of the experiment where you take a mixture of ice and water, plop some salt in there and the temperature of the solution progressively drops. The salt increases the entropy ...
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1answer
44 views

How do I know which is the “correct” way to write the reaction?

We need to calculate the heat produced by a set of $\mathrm{N_R}$ reactions in our reactor model. \begin{align} \mathrm{Q_r = \sum_{j=1}^{Nr} Rr_j*\Delta H_{R,j}} \end{align} $\mathrm{Rr_j}$ is the ...
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Basis set in the computational software “Gaussian-03” for studying adsorption of a hydrogen atom on a carbon paste electrode dropcasted with Pt-CNT

What is the basis set in the computational software "Gaussian-03" that can be used to study the interaction of $\ce{H}$-atom with $\ce{Pt-CNT}$ dropcasted electrode? How can we study the energy ...
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1answer
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What is the precise definition of W$_{max}$ in the context of electrochemistry and thermodynamics?

I'd like clarification of the meaning of $W_\mathrm{max}$ in the following equations (and thus in the combined result in the third equation): \begin{align} W_\mathrm{max} &= \Delta G\\ ...
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1answer
156 views

What is the relation between surface tension and initial molecular harmonic?

Initial harmonic is measured as Hartree/Bohr^2 ( like IHarmonic=n in Gaussian Software ). As I am from physics background I am used to look at features from their dimension point of view: Actually ...
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1answer
43 views

Help on a problem determining how much water would freeze in the solution

I came across a problem, I cannot solve in my 12th Grade Chemistry magazine .It goes like this A solution is prepared by adding 20 gram of Urea (Molecular Weight - 60 gram/mole) in 100 gram of ...
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2answers
300 views

Is the 'n' in Delta G = -nFE, ever negative?

Is it possible for 'n' to ever be negative? Trying to figure out where I went wrong on some thing and want to rule that out.
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66 views

How can I work out the entropy change of benzene when it changes from vapour into liquid?

I’m stuck on a particular problem which I can’t work my head around: Information has been given that: The boiling point of benzene at atmospheric pressure is $353~\mathrm{K}$ and the enthalpy of ...
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2answers
51 views

Does the third law of thermodynamics apply to all compounds and elements?

According to wikipedia, the third law of thermodynamics is "The entropy of a perfect crystal, at absolute zero (zero kelvins), is exactly equal to zero.". Then, theoretically, could all substances, ...
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1answer
65 views

Is ln(K2/K1) = (∆h°rxn/R)(1/T1 - 1/T2) even when ∆h°rxn varies strongly with temperature?

In all of my physical chemistry books I find the same expression for estimating the equilibrium constant of a reaction at a non-standard temperature. The derivation starts with $R \ln K_\text{eq} = ...
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Given a forward reaction with positive enthalpy, is its reverse reaction be endothermic or exothermic?

I'm pretty sure the sign changes. But, I want to be sure if it becomes endothermic or exothermic.
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1answer
36 views

Why do exothermic dissolution reactions occur?

I've always been taught that an exothermic dissolution means that the forming of solute-solvent bonds releases more energy than the energy consumed to break solute-solute bonds and solvent-solvent ...
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0answers
14 views

How much ice will reduce the chicken carcass temperature from 32 to 8 degree C

I am interested to learn through heat claculations the quantity of ice that would achieve a chicken carcass core temperature of 8 degree C. My chilling tank has a volume of 15,000 liters of flowing ...
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1answer
53 views

Predict Entropy based on the Balanced Equation

You cannot use values but must determine from looking The equation I have trouble with is as follows: $$\ce{2Na(s) + 2H2O(l) -> 2NaOH(aq) + H2}$$ According to my teacher the entropy is ...
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3answers
147 views

Why does everything go in the direction of positive entropy change?

I read about entropy from different sources. Still don’t get why (universal) entropy change has to be greater than zero for irreversible process, i.e. $\mathrm{d}S_\mathrm{Univ}>0$. Is it a result ...
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2answers
63 views

What is the difference between ΔG and ΔG “with an o on top”?

I want to know the difference between $\Delta G$ and $\Delta G$ "with an o on top"? I couldn't figure it out. Ex: $\Delta G^\circ = -RT\ln K$ $\Delta G = \Delta G^\circ + RT \ln K$ What is the ...
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1answer
68 views

Why is it that increasing the molar mass generally increases the Entropy? [closed]

I've just found read that entropy increases through these reasons: Changing the phase of the elements to a gas. Increasing the molar mass of that specific element increases the entropy. I ...
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1answer
30 views

Hess's Law - enthalpy of combustion

The enthalpy of combustion of a solid carbon to form carbon dioxide is $-393.7\ \mathrm{kJ/mol}$ carbon, and the enthalpy of combustion of carbon monoxide to form carbon dioxide is $-283.3\ ...
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1answer
165 views

Exo- or endothermic? Clarification required regarding a few cases

Are the following processes exothermic or endothermic? a) When solid $KBr$ is dissolved in water, the solution gets colder. b) Natural gas ($CH_4$) is burned in a surface. c) When concentrated ...
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1answer
61 views

How to determine whether the enthalpy of solution is positive or negative by calorimetry?

How can we determine if the enthalpy of solution of a compound is positive or negative? In order to make a clear idea about what I mean, take the following problem: A 3.5 g sample of $\ce{NH4NO3}$ ...
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1answer
89 views

Is time a measurement of Entropy?

Is time a measurement of entropy? Is it because time is increasing forever? Well after reading about the Second Law of Thermodynamics and working with Entropy, I began to realize that if time can be ...
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4answers
72 views

Gibbs Free Energy of Solutes and Solutions

Using the equation $$\ce{CaSO4 (s) <=> Ca^2+ (aq) + SO4^2- (aq)},$$ and $\Delta H/\Delta S$ values, calculate $\Delta G$ at $50~^\circ\mathrm{C}$ when the solution is saturated with $\ce{Ca^2+}$ ...
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2answers
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What causes spray cans to get cooler when shaken?

I've been searching the web for this phenomenon and surprisingly I found only one post about it. And the reply to this question about canned air begins with words: I don't know about the shaking ...
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Why does water evaporate spontaneously at room temperature despite dG > 0?

Standard Gibbs free energy of formation of liquid water at 298 K is −237.17 kJ/mol and that of water vapour is −228.57 kJ/mol. Therefore, $$\ce{H2O(l)->H2O(g)}~~\Delta G=8.43~\mathrm{kJ/mol}$$ ...
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How to determine the bond enthalpy of the phosphine chlorine bond? [duplicate]

How to determine the bond enthalpy of P-Cl in the equation: $$\ce{PH3 + 3HCl -> PCl3 + 3H2}$$
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Ways to change the spontaneity of a reaction

I can think of any other way to influence the value of $\Delta G$ than (1) change the temperature (2) providing an external source to overcome the negative cell potential The relationship between ...
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How do tie-line slopes affect raffinate/extract envelope in ternary phase diagrams?

I am struggling to understand ternary phase diagrams for reactor engineering. The course slides offer little to no help so I'm hoping to find an answer to this question How does the slope of the ...
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1answer
38 views

Relating Delta E (U) to Delta H question

The question is For which exothermic reaction is $\Delta\,E$ more negative than $\Delta\,H$? (A) $\ce{Br2(l) <=> Br2(g)}$ (B) 2C(s) + O2(g) r 2CO(g) (C) $\ce{H2(g) + F2(g) ...