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.

Filter by
Sorted by
Tagged with
1
vote
1answer
36 views

How to find the Cp, difference of Cp and heat of fusion from the dependence of vapor pressure on temperature?

The vapor pressure of zinc varies with temperature as $$\log P(\pu{mm Hg}) = -6850/T - 0.755\log T + 11.24 \label{eqn:1}\tag{1}$$ and that of liquid zinc as $$\log P(\pu{mm Hg}) = -6620/...
1
vote
0answers
37 views

How to I find the equilibrium temperature in this problem?

From Castellan's Physical Chemistry, chapter 12 [1, p. 276]: 12.18 At $\pu{25 °C}$ we have for rhombic sulfur: $ΔG_\mathrm{f}^\circ = 0,$ $ΔS^\circ = \pu{31.88 ± 0.17 J K-1 mol-1};$ and for ...
1
vote
1answer
47 views

Constant Pressure and Temperature during Phase Change

One of the solution guides to a question I was working on said that pressure and temperature is constant for a phase change. I understand why temperature is always constant for a phase change, but don'...
2
votes
1answer
52 views

Application of Nernst Equation in Potentiometric titration of Fe2+ with Ce4+

It is well Known that to find $E_{cell}$ during titration of $Fe^{2+}$ with $Ce^{4+}$ we consider 3 domains: Before Equivalance point , $E_+ = E_{Fe^{3+}/Fe^{2+}}^o+\frac{RT}{nF}log\frac{[Fe^{3+}]}{...
3
votes
2answers
3k views

Is enthalpy the same thing as potential energy?

From what I know in a closed system the potential energy + the kinetic energy is constant since no external work is done on the system. In my textbook it says that enthalpy is equal to the sum of the ...
15
votes
4answers
26k views

Beer freezing after being opened

I am watching the Stoke vs Swansea game, & to be honest, it's pretty boring. So much so, that I've started to wonder why it is that my beer has turned into a slushy after being taken out of the ...
-4
votes
0answers
18 views

Show that the following processes are irreversible [on hold]

Show that the following processes are irreversible. (a) Gas freely expands from V to V+dV (dV>0) adiabatically, and (b) Gas expands adiabatically from p to p+dp (dp<0) via the Joule-Thompson ...
-1
votes
1answer
42 views

Boiling point elevation does not depend on the solute? [on hold]

I've recently carried out an experiment trying to measure the boiling point elevation of water after adding 5M of NaCl and KCl. Although for some reason, KCl solution started boiling around 90 degree ...
-1
votes
0answers
32 views

What is the ΔG* value for nucleation? [closed]

To be honest, I would like to know how $\Delta G^*$ is different from $\Delta G$ in general and whether the star has any other significance. Now, moving to the second question. I was asked to find $\...
0
votes
0answers
27 views

Software to predict equilibrium products in the ideal gas phase

I'm interested in software packages that can answer the following kind of question: If I mix 30mol% $N_2$ and 70mol% $H_2$ together at 2 bar and 2000C, what is the equilibrium composition after all ...
-1
votes
0answers
47 views

Chemical Equilibrium problem

I can't seem to get the answer that appears on the back of the book Here is what i did: a) $K_p=K_x p^{\Delta N}$; in this reaction $\Delta N =-1$, then $K_pp=K_x$ from $\Delta G=-RT\log K_p$ I ...
5
votes
2answers
28k views

How can I find the heat that will be released in kJ per gram for the reaction of Al with Fe2O3?

Find the heat that will be released in kJ per gram when aluminium ($\ce{Al}$) reacts with $\ce{Fe2O3}$ as follows: $$\ce{2Al(s) + Fe2O3(s) → Al2O3(s) + 2Fe(l)}$$ The information given is: $\Delta ...
0
votes
3answers
47 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 ...
2
votes
2answers
78 views

Temperature measurement

Consider some liquid in a beaker. I am measuring its temperature using a thermometer. When i put my thermometer's bulb in the liquid, the particles of the bulb gain the same kinetic energy as of the ...
8
votes
1answer
424 views

Ag-Sn-Cu Phase diagram to formulate homogenization temperature / duration

I am working on Ag-Sn-Cu alloy phase diagram to figure out the best temperature / duration to homogenize the alloy (annealing). The %age of elements in the alloy are Ag - 40 % Cu - 27.8 % Sn - 32.2 % ...
6
votes
1answer
173 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 ...
8
votes
1answer
236 views

Based on their respective number of degrees of freedom, what's the most efficient fuel; hydrogen or gasoline?

The reaction of octane's combustion is: $$\ce{2 C8H18 + 25 O2 -> 18 H2O + 16 CO2}$$ I am asked for computing the number of degrees of freedom of the octane given that its specific heat is $\pu{...
1
vote
0answers
37 views

What is the degree of freedom of the calcium carbonate dissociation reaction?

Question $\ce{CaCO3}$ dissociated in a closed system according to the reaction: $$\ce{CaCO3(s) -> CaO(s) + CO2(g)}$$ Assuming the reaction is in thermodynamic equilibrium, what is/are ...
1
vote
2answers
29 views

Spontaneity of an exothermic chemical reaction

When the process is exothermic (ΔHsystem​<0), and the entropy of the system increases (ΔSsystem​>0), the sign of ΔGsystem​ is negative at all temperatures. Thus, the process is always spontaneous. ...
-1
votes
0answers
33 views

Calculating heat of neutralisation

Two acids $\ce{HX}$ and $\ce{HY}$ have strength ratio $5:2$. Their heat of neutralisation are in ratio $5:4$. If $40\ \mathrm g$ of $\ce{NaOH}$ is added to a mixture of acids containing $1\ \mathrm g$ ...
1
vote
4answers
72 views

Basic concept of the first rule of thermodynamics

There is a cylinder-piston system with some gas in it, and let's say this system is a closed system. Say that the system is submerged in a large beaker of water whose temperature is $25\ \mathrm{^\...
-1
votes
1answer
27 views

What is the the total heat extracted in the process? [closed]

Since this is a cyclic process:- Change in internal energy=0. In the process C-A the work done W is zero, thus the heat Q is zero since it is an isochoric process. Next in the process A-B, I got the ...
0
votes
2answers
47 views

Temperature measurement using thermometer [closed]

I have two samples of water – 'A' and 'B'. My thermometer measured them to be 90 °C. They both have different volumes. So, the kinetic energy of the particles of sample A and B is same or different? ...
11
votes
3answers
18k views

Relation between constant-pressure and constant-volume heat capacities: Cp - Cv = nR

For an ideal gas, we have $$C_p - C_V = nR$$ where $C_p$ is heat capacity at constant pressure, $C_V$ is heat capacity at constant volume, $n$ is amount of substance, and $R=N_\mathrm A\cdot k_\...
4
votes
2answers
125 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^\...
0
votes
3answers
1k views

Are all volatile liquids combustible?

I realized that liquids like petrol, kerosene and even perfumes are combustible when they are volatile. Could that be the reason why water is not combustible is because it is not volatile? Are ...
1
vote
0answers
35 views

Identifying endothermic and exothermic reaction [closed]

How can I know that a given reaction is endothermic or exothermic? I know that all combustion reactions are exothermic. But what about other reactions? In my school exam I was asked about whether the ...
1
vote
0answers
42 views

Calculating thermodynamic quantities for hydrogenation of iron nitride

HW#6.3 If the reaction $$\ce{Fe2N(s) + 3/2 H2(g) <=> 2 Fe(s) + NH3(g)}$$ comes to an equilibrium at a total pressure of $\pu{1 bar},$ analysis of the gas shows that at $\pu{700 K}$ ...
2
votes
0answers
76 views

Why can't calorimetry be used to measure fast reactions?

As my previous post was a bit unclear and unspecific, I am reformulating it. First of all this is a question that I had while reading some concepts my book introduces, so this isn't a homework ...
1
vote
2answers
69 views

How to calculate the standard Gibbs free energy of formation of bromine vapor at room temperature?

The normal boiling point of liquid bromine is $\pu{58.2 ^\circ C}$. At $\pu{9.3 ^\circ C}$ the equilibrium vapor pressure of liquid bromine is $\pu{100 torr}$. From this data, calculate the standard ...
4
votes
2answers
191 views

Clausius–Clapeyron relation for states of water and vapor

I've seen many questions about this topic on this site, but I still have some issues trying to understand this aspect. Here's what I believe I understood looking at the phase diagram for a pure ...
3
votes
1answer
196 views

Relation between First Law of Thermodynamics and Ideal Gas Law

Thermodynamics has always been a tough thing for me. There are lots of assumptions in this subject (those assumptions, I know, are necessary, I know the science of thermodynamics is a very practical ...
0
votes
1answer
44 views

Entropy changes during transfer of heat between two bodies

Consider two metal blocks, one at 500K and another at 300K, they are bought to contact with each other until they reach a common temperature. Find the entropy change of each object and the total ...
0
votes
0answers
24 views

Reaction between chlorine gas and oxygen at 600 degrees Centigrade

Chlorine gas will not normally react with oxygen gas directly at STP. However, would the two react at standard pressure and 600 degrees Centigrade?
3
votes
1answer
67 views

Thermodynamic vs kinetic basicity [closed]

I'm writing something related to basicity and came across few papers that distinguish thermodynamic and kinetic basicity. "In particular, the study of hydrogen bonding (H-bonding) within proton ...
0
votes
1answer
44 views

Entropy for a closed system [closed]

Case -1 In a free expansion of an ideal gas in a region or container, we cannot trace a pressure-volume path since the pressure, temperature and volume of the gas fluctuate unpredictably when the gas ...
6
votes
2answers
131 views

Tunneling in chemical reactions

We know that quantum tunneling is the reason behind several natural phenomenon like alpha decay and thermonuclear fusion inside the stars. How can it influence chemical reactions by tunnelling a ...
1
vote
1answer
30 views

Boiling point elevation and liquid solutions

$\pu{1 L}$ of an aqueous solution of urea having density $\pu{1.06 g mL-1}$ is found to have elevation in boiling point $\Delta T_\mathrm{b} = \pu{0.5 °C}.$ If the temperature of this solution is ...
7
votes
2answers
19k views

Is graphite more stable than diamond?

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 der ...
0
votes
1answer
61 views

I was told that the more exothermic the solution, the more soluble the salt. Is this statement wrong?

I was also told that $$\Delta H(\text{solution}) = \Delta H(\text{hydration}) - \Delta H(\text{lattice E})$$ However, for $\Delta H(\text{solution})$ to be exothermic, it has to have a negative value ...
1
vote
2answers
80 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, $...
1
vote
0answers
16 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 ...
1
vote
1answer
121 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{\...
11
votes
1answer
709 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 $\ce{P=O}$ ...
7
votes
5answers
2k views

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 ...
1
vote
1answer
98 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 $\pu{13.33 ^\circ C}$...
12
votes
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 &...
2
votes
0answers
27 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 ...
3
votes
3answers
252 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 ...
0
votes
1answer
58 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 ...