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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21 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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0answers
11 views

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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2answers
55 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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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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0answers
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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0answers
19 views

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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0answers
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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0answers
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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1answer
595 views

Explanation of the strength of phosphorus-oxygen bond

When discussing the Wittig reaction, Clayden's Organic Chemistry cites the strength of the $\ce{P=O}$ formed in triphenylphosphine oxide as a driver of the reaction through enthalpy: The $\ce{P=O}$ ...
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5answers
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What is the lower bound to the temperature at which a fire can burn?

To have a fire, you need 1) oxygen, 2) fuel and 3) heat. You can have different fuels that burn at different temperatures, but you always need some amount of heat to have a fire. If you can use any ...
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1answer
91 views

Extrapolating from a calorimetry lab to find a new delta T with different volumes and grams of substance

So, we just finished an AP chem lab where the question was basically: Given the results of the lab were that $\pu{5 grams}$ of $\ce{CaCl2}$ and $\pu{45ml}$ of water produced a $\pu{13.33 ^\circ C}$...
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1answer
162 views

Apparent contradiction in the type of deviation of an ethanol-water mixture

For a mixture of $\ce{EtOH}$ and $\ce{H2O}$: $\Delta H_{\text{mix}} < 0$ (exothermic) and $\Delta V_{\text{mix}} < 0$ (volume contraction). This means that the unlike interactions are stronger ...
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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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0answers
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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1answer
6k views

Is adsorption exothermic, and if so, why?

Why is adsorption exothermic? The explanation given in my textbook is: For a process to be spontaneous, the thermodynamic requirement is that, at constant temperature and pressure, $\Delta G &...
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0answers
9 views

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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0answers
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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3answers
245 views

How can residual entropies be reconciled with the Third Law?

The third law of thermodynamics states that the absolute entropy of a pure crystalline substance is $0$ at $0\,\mathrm{K}$. In the analysis of chemical reactions this absolute scale is sued to ...
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1answer
56 views

Current in a Lithium Ion Battery

I am trying to find the current transferred to the anode and cathode of a Lithium Ion Battery at different voltages. I know the temperature (approximately) of the battery, the battery's starting ...
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1answer
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
99 views

What is Delta H for dissolution?

An ionic compound has a solubility of $1\ \mathrm M$ in water at $25\ ^\circ \mathrm C$ and its solubility increases as the temperature is raised. What are the signs of $\Delta H^\circ$ and $\Delta S^\...
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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
743 views

Is the E in Arrhenius equation the change of enthalpy?

I'd like to know whether the activation energy in Arrhenius equation is the enthalpy difference between the transition state and the reactant. If it's not enthalpy, is it Gibbs energy or something ...
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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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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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1answer
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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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
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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1answer
2k views

Thermal decomposition of calcium carbonate

Thermal decomposition of calcium carbonate. In general, we heat $\ce{CaCO3}$ to temperature of approximately 825°C it decomposes into calcium oxide and liberates carbon dioxide gas:* $$\ce{CaCO3} \...
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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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25 views

Impact of pH? Change in Binding Affinity of protein-ligand complex based on pH and Kd?

When the $\mathrm{pH}$ was $5.0$, the temperature was $\pu{25 °C}$,the $K_\mathrm{D}$ was $\pu{5 μM}$, and [L] was equal to $K_D$, the protein(s) were half bound. Question considers half bound ...
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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
3k views

What happens to water under high pressures without possibility of escape?

Knowing very little about the nature of water, wondering how it might behave at the centre of a planet or centre of an another massive gravitational body. Could water take such pressures or might it ...
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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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3answers
2k views

Why does thermodynamics only apply to macroscopic systems at equilibrium?

A text says: The laws of thermodynamics deal with energy changes of macroscopic systems involving a large number of molecules rather than microscopic systems containing a few molecules. ...
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0answers
22 views

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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2answers
10k views

Is molarity an intensive property?

$$\mathrm{molarity} = \frac{\text{amount of solute}}{\text{volume of solution}} $$ and amount of substance is based on quantity (larger mass means larger amount), so how come it is an intensive ...
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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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2answers
4k views

Why are hydrogenation reactions exothermic?

I learned that all reactions that yield hydrogen are endothermic (such has reforming) and reactions that use up hydrogen are exothermic (FCC cracking, hydrogenation, etc.). But why is this so? I know ...
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5answers
107k views

Difference between thermodynamic and kinetic stability

What is the difference between thermodynamic and kinetic stability? I'd like a basic explanation, but not too simple. For example, methane does not burn until lit -- why?
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4answers
11k views

Spontaneous/Non-Spontaneous Reactions and Reversible Reactions

My chemistry textbook states "Reversible reactions constitute a limiting case between spontaneous and non-spontaneous processes." Does this mean that some of the reversible reactions are spontaneous ...
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3answers
2k views

Does an irreversible reaction have an equilbrium between reactants and products?

Retrospective analysis 2/13/2017 -- The barium sulfate example is a poor choice. Equilibrium equations should really be defined using activities, and the activity of solid barium sulfate is by ...
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1answer
177 views

Why does Gibbs free energy correspond solely to non-expansion work?

First of all: I know this question has been asked before (Why does the Gibbs free energy only correspond to non-expansion work?), and although I understand the mathematical derivation given there, I ...
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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 ...