Questions tagged [thermodynamics]

Applicable to questions about heat, energy, work, and their interconversion in chemistry. See the tag wiki for a detailed list of topics. Questions tagged may also be tagged with [enthalpy], [energy], [free-energy] where appropriate.

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23 views

Boiling point elevation and liquid solutions

$\pu{1 L}$ of an aqueous solution of urea having density = $\pu{1.06 g/mL}$ is found to have $\Delta T_b$ (elevation in boiling point) = $\pu{0.5° C}$. If the temperature of this solution is increased ...
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Computing enthalpy of formation of dissolved gas from its enthalpy of dissolution

Provided that I know the enthalpy of formation $\Delta H_f^0(X_{g})$ of a substance $X$ in gas phase and its enthalpy of dissolution $\Delta H^0_{sol}(X)$ in the same conditions, considering that the ...
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14 views

Equation for the temperature of a heated object [on hold]

You're given the mass and specific heat of an object and told that, after it's heated, it's placed in a bucket of water w/ x mass and x temperature and then given the resulting temperature. When ...
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2answers
59 views

How to derive this temperature-pressure-specific volume relationship?

(for isentropic, adiabatic, ideal gas flow) $$\frac{T_x}{T_y} = \left(\frac{p_x}{p_y}\right)^{\frac{(\gamma-1)}{\gamma}} = \left(\frac{V_y}{V_x}\right)^{\gamma-1}$$ where $V$ is the specific volume, $...
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32 views

Data of phase diagram of water?

I am trying to build a mathematical model that represents the curves of a phase diagram. Is there somewhere I can find the data points of the phase diagram of distilled water?
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1answer
117 views

Finding the isotherm with given minima

Get the temperature of the isotherm for water for which the local minimum is at $\pu{100 Pa}.$ Use the values of $a$ and $b$ of water. My approach In the van der Waals equation, set $$\frac{\...
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14 views

Effect of the reaction stoichiometric coefficients on Δn [on hold]

We have ΔH=ΔE+RTΔn for any chemical reaction (suppose ideal gases) where Δn is the difference between the stoichiometric coefficients of the gaseous products and gaseous reactants. Note that ΔH in J/...
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Calculating triple point using freezing and boiling point depression

On this website, I read that when an solute(lets say NaCl) is added to a solvent(lets say water),the boiling point and melting point shift by a certain amount. If, in our experiment, we keep the ...
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31 views

What would the transition state look like for the following reaction? And a question on Gibbs free energy of the Transition State [closed]

The alkaline hydrolysis of ethyl acetate. Also wanted to know whether the addition of solvent would have an impact on the Gibbs free energy value of the Transition State since the transition state ...
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22 views

Reaction between TiCl2 and Cl2 and 600 degrees C [closed]

Will TiCl2 (s) and Cl2 (g) react to form TiCl4 (g) at 600 degrees C?
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27 views

Two methods for calculating ΔH yield different results [closed]

A problem in my book says: $\pu{140 g}$ of $\ce{N2}$ (perfect gas) changes from $\pu{200 K}$ to $\pu{400 K}$ at constant volume. Calculate the change in internal energy $\Delta E$ and the change in ...
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Uncertainty calculation help! Eyring Plot [closed]

If I am looking at the Eyring equation, lnk/T = −ΔH†/RT + lnkB/h + ΔS‡/R, how can i proceed with my uncertainty calculations?
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25 views

What is total enthalpy?

I've seen that it's defined as $h_0 = h + \frac{v^2}{2}$, where $h_0$ is the total enthalpy per unit mass. I can see that the $\frac{v^2}{2}$ term probably has something to do with kinetic energy, but ...
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236 views

Is the equation dG = Vdp − SdT valid only for a reversible process? Can it be applied for an irreversible one too?

In the derivation, we write: $$ \begin{align} G &= H - TS &\quad&\to&\quad \mathrm dG &= \mathrm dH - T\,\mathrm dS - S\,\mathrm dT \\ H &= U + pV &\quad&\to&\quad ...
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1answer
37 views

Why aerosol forms when you take a hot shower in a very cold day? [closed]

When temperature is about $\pu{17 ^\circ C}$ and I open the hot shower in maximum temperature (for a common electric shower) the air gets almost immediately full of droplets and this lasts the entire ...
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1answer
44 views

What is the meaning of the phase state label (cr,l) appearing in ATcT thermochemical data tables?

I was examining data associated with this post on the heat of solution of ammonium nitrate when I came upon the NIST ATcT data page which lists the heat of formation of $\ce{(NH4)NO3(cr,l)}$. In this ...
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2answers
32 views

Why does a NOx container get cold when NOx is released? and What is the relationship of the vapor pressure curve with the liquid-vapor dome?

The temperature at which $\ce{NO_x}$ is in equilibrium with its liquid and vapor phase at 1 atm is about –84 °C. Does that mean $\ce{NO_x}$ exists as a liquid at that temperature? What about it's ...
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1answer
24 views

Applying Raoult's Law in volatile solids–liquid solutions

My textbook explains applying Raoult's Law for the two cases: liquid–liquid solutions, in which the vapour pressure of the solution is due to both the components non-volatile solids–liquid solutions, ...
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27 views

How do you find the heat capacity ratio of combustion products?

For example, if gaseous oxygen $(O_2)$ and paraffin wax $(C_{32}H_{66})$ were to stoichiometrically combust at STP, how would one go about finding the heat capacity ratio ($\gamma={c_p \over c_v}$) of ...
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2answers
57 views

Coffee cup lids

So this morning I purchased a coffee. As a not uncommon event the lid on the coffee cup didn't have a hole completely punched through (a gas inflow hole). This makes it difficult to drink the coffee ...
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1answer
494 views

The heat content of the products is more than that of the reactant in an … reaction

The heat content of the products is more than that of the reactant in an ............. reaction. In this question the answer given is "exothermic"; yet I thought the answer would be endothermic as ...
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1answer
77 views

How can I calculate the equilibrium constant for this reaction?

Silver(II) oxide partially decomposes into solid silver and oxygen gas according to: $$\ce{2 AgO(s) <=> 4 Ag(s) + O2(g)}$$ with enthalpy $H^\circ = \pu{62.0 kJ}$ and entropy $S^\circ = ...
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1answer
37 views

What's greater, enthalpy of combustion or heat of combustion? [closed]

What is the difference between the two? In my assignment book there is this question which asks if enthalpy of combustion is greater than, equal to or less than the heat of combustion. The answer ...
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1answer
52 views

Relationship between Gibbs free energy and potential energy (related to reaction coordinate diagrams)

For a rate law, the rate constant $k$ is given by the equation $$\ln k = \ln A - \frac{E_\mathrm{a}}{RT}\tag{1}$$ If $k_\mathrm{fwd}$ is the forward rate constant and $k_\mathrm{rev}$ is the reverse ...
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How are standard enthalpy of formation values determined?

How are standard enthalpy values of formation determined? And how do you determine other enthalpies, such as the enthalpy of hydration? I'm really confused as to where they got their numbers from.
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41 views

Finding a Certain Coolant [on hold]

Is there a highly endothermic chemical with a thermal conductivity coefficient greater than 0.1 that could be exposed to 600 degrees Celsius but only heat up to 100 degrees Celsius? Preferably, this ...
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0answers
18 views

Heat of neutralization [duplicate]

(1) Why heat of neutralization of weak acid by strong base is always less than -57 kJ/mol? (2) How does heat of neutralization depend on the strength of the acids and bases used?
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47 views

Equilibrium constant when mixing HCl and NaOH

I have 300 ml of a 1 M $\ce{HCl}$ solution and 400 ml of a 1 M $\ce{NaOH}$ solution. These are now mixed at a constant pressure and a temperature of 25 °C. The following neutralization reaction takes ...
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1answer
42 views

Facing a problem in enthalpy calculation

If 1 mole of gaseous carbon atoms are converted into diamonds, calculate enthalpy change of process given that bond enthalpy of $\ce{C-C}$ bond is $\pu{400 kJ mol-1}.$ According to me, the answer ...
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25 views

Thermodynamics of Acid Base Neutralisation

I was attempting an exam in which they questioned us about the thermodynamics of acid-base reaction. The question was this: In neutralisation reaction of a strong acid and a strong base in a ...
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39 views

Diffusion between phases based on chemical potential

How is the concept of diagram(b) different from that of (e) and (d) from (f)?Someone told me in one of my earlier posts (Why will A atoms diffuse from β phase to α phase and B atoms from α phase to β ...
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20 views

Enthalpy of formation at other temperatures

I was told each compound has an enthalpy of formation of 0 at the standard temperature if it is in it's lowest energy modification. But what if we change the temperature? It would make sense to me ...
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50 views

Why will A atoms diffuse from β phase to α phase and B atoms from α phase to β phase?

At the initial compositions 1 and 2 of $α$ and $β$ respectively the chemical potentials of A and B atoms in each phase can be found by extrapolation of the tangents to the free energy curves at 1 and ...
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1answer
31 views

Why does a system want to achieve randomness to be feasible? [closed]

According to entropy and gibbs free energy, randomness is one of the factors that determines reaction spontaneity, but why? Shouldn't it be the opposite?
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1answer
78 views

What is the reason for phase separation? [closed]

I have seen phase separation as a phenomenon taking place. However I do not understand why this phenomenon occurs as a counter example to the natural laws of diffusion along the concentration gradient....
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2answers
111 views

Does energy come from fuel or oxygen? (surprise?)

Question: Is it oxygen or fuel that releases energy during burning? The answer from this article: Why Combustions Are Always Exothermic, Yielding About 418 kJ per Mole of O2 (Journal of Chemical ...
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1answer
55 views

Lowering the melting point of water with salt

I was trying to calculate amount of salt needed to lower the melting point of water by 5 °C. According to my solutions, I need to make sure $$n\mu(\ce{H2O(s)}) =n\mu(\ce{H2O(l)})+ RT\log(x)$$where $ x=...
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1answer
70 views

Why enthalpy changes in phase transition when there is no change of temperature?

Why there is a change in enthalpy in phase transition? I'm asking because enthalpy depends only on temperature: $$\mathrm dH = C_p\,\mathrm dT,$$ and the change in temperature is $\mathrm dT = 0.$
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16 views

For a gas having molar mass M, express specific heat at constant pressure in terms of heat capacity ratio

For a gas having molar mass $M$, express specific heat at constant pressure in terms of heat capacity ratio. My attempt: using $ C_p - C_V = R $ and $ \dfrac{C_p}{C_V} = \gamma $ $ C_p = \dfrac{...
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1answer
39 views

Why do we use Ḡ (“G bar”) as a notation for partial molar free energy?

For partial molar entropy there is a bar that is positioned above the $G$ with a subscript I that is sometimes added to the $G~(\bar{G}).$ The bar I read sometimes denote the "partial nature of the $G$...
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Why is the y intercept of a G vs X curve treated as chemical potential?

Whenever I am to prove the fact that the $y$ intercept to the $G$ vs $X$ curve is basically my chemical potential, there are two equations that need to be assumed. One is $$G=\mu _{A}X_{A}+\mu _{B}X_{...
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3answers
586 views

What do the horizontal lines in a P-V phase diagram mean?

I have been studying phase diagrams of pure substances, and for a substance such as carbon dioxide for example, it's diagram looks something like this: The horizontal lines in the liquid phase puzzle ...
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2answers
51 views

When boiling water, how is evaporation rate affected by the surface area of the container?

Imagine two pots boiling on a stove. One is tall, while one is wide. Both contain the same volume of water. What will be the difference in the rate of evaporation between the two containers?
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37 views

Why does silver (I) have a larger lattice enthalpy and hydration enthalpy than sodium?

The ionic radius of the $\ce{Ag^+}$ ion is $129$ pm, and that of the $\ce{Na^+}$ ion is $116$ pm. Since the sodium ion is smaller than the silver ion, it makes sense that it has a stronger polarizing ...
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40 views

Calculating ideal chemical work using extent of reaction and chemical potential

I have a electrochemical reactor assumed isothermal and isobaric with 4 reactions and I am trying to calculate the "ideal chemical work' exerted by each reaction using the extent of reactions for each ...
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36 views

Entropy in organic chemistry

Why do we not talk about entropy when deciding feasibility of an organic reaction?...We always seem to only be interested in stability of product and intermediate(essentially delta H)and draw their ...
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1answer
30 views

How to explain Gibbs free energy is a pressure-dependent state function?

I'm aware that through deriving Gibbs free energy to infinitesimal changes, we could get the formula: $\mathrm dG = V\,\mathrm dp - S\,\mathrm dT$, giving that Gibbs free energy is pressure-dependent. ...
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1answer
33 views

Question about calculating enthalpy change

$$\Delta H = \left( \begin{array}{c} \text{total enthalpy of}\\ \text{bonds broken}\end{array}\right)-\left( \begin{array}{c} \text{total enthalpy of}\\ \text{bonds made}\end{array}\right)$$ $$\Delta ...
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0answers
48 views

How to calculate the value of heat absorption/ heat release during water electrolysis?

The overall reactions with the enthalpies of water electrolysis at room temperature can be represented by the equation below: $$\ce{2H2O + \pu{237.2 kJ mol-1} + \pu{48.6 kJ mol-1} → 2 H2 + O2}$$ ...
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2answers
80 views

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 ...