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

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1answer
893 views

Why is NaCl3 possible?

There. And there. Almost a year ago, a group of scientists claimed to have reached compounds of $\ce{Na}$ and $\ce{Cl}$ with weird stochiometries ($\ce{NaCl3, Na3Cl, NaCl7, Na3Cl2}$ and $\ce{Na2Cl}$). ...
2
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1answer
20 views

Decomposition of hexaurea-chromic-chloride-trihydrate

I am sitting over a TG diagram of the decomposition steps of hexaurea-chromic-chloride-trihydrate ($\ce{[Cr(CO(NH2)2)6]Cl3 \cdot 3 H2O}$) and cannot really make sense of the products it might ...
0
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0answers
20 views

Stirring the reaction between hydrochloric acid and a powdered substance

For an experiment, I'm adding several substances (as powders) to hydrochloric acid, and measuring the temperature changes to calculate enthalpy. However when adding the powders, the mixture requires ...
1
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1answer
38 views

Exercising to use up energy consumed

Suppose I eat a whole $450~ \rm{g}$ chocolate Easter rabbit. The enthalpy of combustion of chocolate is $−22.4~\rm{ kJ/g}$. One kilogram of body fat contains $39000 ~\rm{kJ}$ of energy. Walking for an ...
3
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1answer
28 views

How to lose as little heat as possible to the surroundings from an endothermic reaction?

For an experiment, I'm adding several substances (as powders) to hydrogen chloride, and measuring the temperature changes to calculate enthalpy. What is a container I could perform it in (other than a ...
2
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1answer
31 views

Spontaneous Reaction and Gibbs Free Energy

I know how to derive the expression for the equilibrium constant starting from $dG=0$, $$\ln(K)=-\frac{\Delta G ^o}{RT}$$ However, if we are not at equilibrium, $dG$ is not necessarily zero. In this ...
3
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1answer
357 views

What's the source of “2.303” in Van't Hoff equation?

I've seen a "2.303" term multiplied to R in Van't Hoff equation several times. Here is one example: http://en.wikipedia.org/wiki/Van_%27t_Hoff_equation#Error_propagation ΔH0 = 2.303 R (logK1 - ...
2
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1answer
47 views

If Gibbs energy of activation is positive, how is the change to the transition state possible?

The Gibbs energy increases from the reactants to the transition state, but according to the Second Law of Thermodynamics, entropy of the universe can only increase. Why is the transition state ...
4
votes
1answer
120 views

What is non-expansion work?

I learnt that Gibbs free energy is the maximum amount of non-expansion work. But the phrase non expansion work confuses me. Work is defined as pressure times change in volume. If there is no ...
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0answers
12 views

What is the justification behind the principle of corresponding states?

Two fluids with same reduced volume and temperature have the same reduced pressure. Two fluids with same reduced pressure and temperature have the same compression factor. What justifies these two ...
0
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1answer
19 views

What is the significance of enthalpy definition not under constant pressure?

Under constant pressure (and only PV work), change in enthalpy can be shown to equal change in heat. If enthalpy is not meaningful outside of constant pressure, then why not use heat instead? So I ...
0
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1answer
24 views

The change in enthalpy of carbon in diamond form to graphite is negative .This suggests that graphite should be more stable than diamond. is it true?

What I thought was that graphite has van derr waal forces while diamond has covalent forces so diamond should be more stable. but the melting point of graphite is more than diamond which implies that ...
1
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1answer
16 views

Heat Capacity temperature dependence and Gibbs energy

I got this problem in school as a tool to get ready for International Chemistry Olympiad, but I have some problems with this challenge. So, the problem is to calculate as precise as possible the Gibbs ...
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0answers
12 views

HHO devices for cars (hydrogen enchancement of fuel burning reaction) [duplicate]

Recently I got quite an interesting offer for increasing my fuel economy (which for my 4.0 liter gasoline engine is quite bad as is) which was an HHO device. What it basically is, as I had it ...
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1answer
32 views

Calculating Energy Change of Acetic acid [closed]

A 10.0 g sample of pure acetic acid (CH3COOH) is completely burned. The heat released from the combustion is used to warm 2.00 L of water from 22.3 ℃ to 39.6 ℃. Assuming no heat was lost to the ...
1
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1answer
84 views

Relative energies between reactants and products

I've been asked to draw a relative energy sketch of the reactants and the two products. The reaction being examined was adding copper acetate monohydrate to glycine in two different fashions to create ...
1
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1answer
60 views

How to calculate the bond energy of C-Cl?

$$\ce{C(s) + 2 Cl2 (g) -> CCl4 (g)}$$ \begin{align} \Delta{}H^\circ_\mathrm{f} (\ce{C(g)}) &= 121~\mathrm{kJ/mol}\\ \Delta{}H^\circ_\mathrm{f} (\ce{Cl (g)}) &= 716~\mathrm{kJ/mol}\\ ...
3
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0answers
23 views

Radial Distribution Function for a Hard Sphere Gas in the Percus-Yevick Approximation - Is There a Quick Way to Evaluate it Numerically?

The question is as in the title. I know that for a one-component hard-sphere gas, there is an analytic solution in the $\vec{k}$-space (PRA, 5, 939). I know that to obtain the correct solution in ...
0
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0answers
43 views

Calculating Vapor Pressure from Delta G/ Kp

For the process, CH3OH(l) --> CH3OH(g) ∆G° = 4.30 kJ/mol at 25 °C. What is the vapor pressure of CH3OH(l) at 25 °C in mm Hg? A) 0.176 mm Hg (B) 14.0 mm Hg (C) 134 mm Hg (D) 759 mm Hg This question is ...
3
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2answers
49 views

Thermochemistry: forms of energy & pressure

I've been in a few classes now that teach about energy, and I feel they're always so bad. There is always such a rush to start using equations to get problems solved, and I often feel I don't have an ...
3
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1answer
40 views

Is there a list of known rate laws for reactions?

I've been scouring the web for a website/pdf that lists reactions and their corresponding rate laws. Something like: \begin{align} \ce{A + B &-> C} & ...
4
votes
1answer
37 views

How many critical points? Why?

Critical points are defined (by wikipedia) as the "end-point of the phase equilibrium curve". I would say this diagram therefore has three critical points. But this is unnatural. I doubt its true. ...
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0answers
17 views

when do we consider the samples in a calorimeter as a solution in calculation?

I noticed some problems consider the samples in a calorimeter as a solution thereby calculating the mass of the combining samples, whereas in others I found that they separate the samples into ...
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0answers
14 views

when do we consider the moles in bomb calorimeter?

When dealing with different problems in thermodynamics I noticed that some of the problem consider the number of moles in calculating the heat absorbed or released, whereas some don't and they deal ...
0
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1answer
25 views

Why is the work done by gas expanding to space is 0 and not infinity?

Suppose there's a spaceship that has a hole in it. Gas is expanding through the hole from the spaceship to outer space (vacuum). According to pressure volume work ($P\Delta V$) the work done by the ...
0
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0answers
7 views

Given the Pair Correlation Functions for a Multi-component Fluid, is There a Simple way to Obtain the Helmholtz Free Energy?

I think it may not be possible. Given all the pair correlation functions, it seems possible to obtain the internal energy (assuming different species interact through pair-potentials (i.e. ...
0
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1answer
18 views

What are the signs for work done by (on?) a gas during isothermal reversible compression?

For the expansion of a gas, isothermally and reversibly, what is the sign taken? Do I use this equation $-nRT\ln (Vf/Vi)$ or this one $nRT\ln (Vf/Vi)$ ? Moreover, when I'm asked about the 'work ...
0
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3answers
69 views

how can decreasing in temperature indicates 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 ...
2
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0answers
59 views

Relationship between thermodynamic reversibility and reactions

Often we're concerned with changes in thermodynamic properties during reactions, like $\Delta H_p = Q_{reaction}$ (change in enthalpy for an isobaric process). What seems odd to me is that in the ...
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0answers
36 views

How to get the final temperature of a constant-pressure calorimeter? [duplicate]

How to get the final temperature given concentration and volume of two solutions, initial temperature and mass of the combined solution and the specific heat of water in a constant-pressure ...
1
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2answers
34 views

How to cancel once-mentioned element in thermochemical reactions

If I have three thermochemical reactions in a series(in order to find the enthalpy change) how can I cancel an element having not included in the reaction that's being asked about? and only mentioned ...
2
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2answers
30 views

Help me understand the correlation between the equilibrium constant and delta G

I understand this up until the last two steps. How does $\text{ln}(K_{eq})$ become $2,303\text{log}(K_{eq})$ and how does $-RT*2,303$ become $-1,42$?
0
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1answer
26 views

Why are enthalpies of reaction or Gibbs FE change given in kJ/mol

It makes no sense to me that these thermodynamic changes are given in kJ/mol. Reactions can have several compounds on both sides and its not clear what exactly the molar variable refers to… I've been ...
0
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1answer
33 views

Real gas expansion

Will a real gas occupy all the space available for it? An ideal gas will expand to fill its container but will a real gas? And what are the changes in a real gas when it expands freely against a ...
0
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0answers
22 views

If we mix Ice and water (both at 0 degree Celsius), does their quantity remain constant?

I was wondering that whether Ice and water mixed (both at 0 degree Celsius) undergo a change in their concentration or not. If not, then does it has nothing to do with equilibrium constant? ...
4
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2answers
66 views

Will all thermodynamic equations have a linear dependence with moles?

I'm taking chemical thermodynamics this semester, and currently seeing things like the Maxwell's Relations. My professor never uses explicitly the variable "n" and always works with molar quantities ...
2
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2answers
40 views

condensation of tellurium on inside of ampoule?

After heating an ampoule of tellurium around its melting point in a furnace for about a day, I've noticed drops of the element on the upper inside surface of the ampoule, as if it condensed there. ...
1
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1answer
18 views

Ideal gasses reaction under const temp and pressure

Conceptual problem: let $A + 2B \rightarrow C + 2D$ be a reaction under constant pressure (P) and temp (T), that goes all the way towards the products. A,B,C,D are ideal gases. let $\Delta H$ be the ...
4
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1answer
27 views

Pre heat coal before burning

So I was wondering if pre-heating coal will improve the efficiency of a steam boiler. I did find that intake air pre-heater and water pre-heater do increase efficiency, but I could not find anything ...
2
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1answer
279 views

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.
3
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2answers
35 views

How do I determine if a process is reversible without numeric information?

How do I determine if a process is reversible without numeric information? It would be nice to know how to determine whether a process is reversible in order to solve problems LIKE this one: A ...
2
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1answer
48 views

Deriving The Triple Point Temperature and Pressure as the following expression

$ΔH_{fus}, ΔH_{vap}, ΔH_{sub}$, as well as ($Tl,Pl$) and ($Ts,Ps$), which corresponds to the temperature and vapor pressure of liquid and solid phrase. My strategies is to use the Clausius-Clapeyron ...
6
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3answers
164 views

Is delta H a state function?

My teacher says $H$ is a state function but $\Delta H$ is not. But I think both of them should be state function. Is he correct?
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0answers
24 views

Why does the sodium acetate solution crystallize by touching? [closed]

As the title stated above, why and how does the sodium acetate solution crystallize by touching?
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1answer
37 views

What is the partial molar volume of epsomite (magnesium sulfate heptahydrate)?

I am trying to calculate the expected volume of an aqueous solution of epsomite and NaCl (308 deg K but willing to go with 298 K as close enough, and 1 atmosphere pressure). I realize the two may ...
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0answers
24 views

How do things heat one another? [duplicate]

For example, how does a gas stove heat a metal pot? A combustion reaction between the gas and the air takes place, and this releases energy due to new chemical bonds being formed. Do the atoms in ...
3
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1answer
43 views

How can enthalpy of a system be negative while entropy is positive?

ΔG = ΔH(system)-TΔS(system) ) When enthalpy is negative, the reaction is exothermic, which means it releases energy into the surroundings. If the system is losing energy, shouldn't the entropy of ...
1
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1answer
30 views

Entropy change of system in adiabatic irreversible process [duplicate]

In an adiabatic irreversible process we know that q = 0. Now change in entropy is defined as q/T. So when q is zero, why is change in entropy not zero ?
3
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1answer
70 views

Why does temperature affect cell potential?

The Nernst equation describes the relationship between cell potential and temperature. But why does temperature affect cell potential? My understanding is that the collision model of kinetics is not ...
3
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2answers
33 views

Why is the volume in this compress gas cylinder constant throughout?

I am stuck on this gas question and its really stressing me out. A compressed cylinder of gas contains $2.25 \cdot 10^3~\mathrm{g}$ of $\ce{N2}$ gas at a pressure of $4.25 \cdot ...