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
0
votes
0answers
54 views

Energy of mercury(II) oxide decomposition

Study check 9.11 from [1, p. 298]: Mercury(II) oxide decomposes to mercury and oxygen. $$\ce{2 HgO -> 2Hg + O2}\quad ΔH = \pu{+182 kJ}$$ […] b. How many kilojoules are needed when ...
1
vote
1answer
43 views

Internal energy change for reactions at constant volume vs constant pressure

The reaction of cyanamide, $\ce{NH2CN(s)},$ with dioxygen was carried out in a bomb calorimeter, and $∆U$ was found to be $\pu{–742.7 kJ mol-1}$ at $\pu{298 K}.$ Calculate enthalpy change for the ...
4
votes
1answer
156 views

How is a phase equilibrium defined for a one-component system?

A question on this site asked whether a one-component system is at equilibrium when melting or boiling, and the disparate answers were somewhat dependent on the definition of phase equilibrium. ...
1
vote
0answers
37 views

Measurement of the lattice energy

The lattice energy of a solid ionic compound is the energy released when one mole of the solid compound is formed from its constituent gaseous ions at $\ce {298 K}$ and $\ce {1 bar}$. However, gaseous ...
2
votes
3answers
195 views

melting and boiling …really equilibrium? [closed]

Why are melting and boiling considered equilibrium processes even though the amount (concentration) of both phases keep changing i.e from solid to liquid and so on?
2
votes
0answers
76 views

Negative Pressures in Van der Waals Equation of State

This is the plot of the Van der Waals equations: As you can see, the Van der Waals equation predicts a "stretched liquid" area (MNS). Is this physically feasible and what exactly happens there? Are ...
0
votes
0answers
75 views

Gibbs free energy of phosphorus pentachloride decomposition reaction

The equilibrium constant at $\pu{227 °C}$ for the equation $$\ce{PCl5(g) <=> PCl3(g) + Cl2(g)}$$ is $K_p = \pu{4.50E3 bar}.$ Calculate the value of $Δ_\mathrm{rxn}G^\circ$ at $\pu{227 ...
6
votes
1answer
194 views

Heat involved in isenthalpic process

Question 28 from [1, p. 4.4]: An ideal gas is expanded irreversibly from $\pu{5 L}$ to $\pu{10 L}$ against a constant external pressure of $\pu{1 bar}.$ The value of heat involved $(q)$ in this ...
4
votes
2answers
115 views

Clarification on the Clausius inequality

In Atkins' Physical Chemistry the criteria for spontaneity using Gibbs energy was calculated using the Clausius inequality: $$\mathrm dS ≥ \frac{\mathrm dq}{T},$$ and at constant pressure, $\mathrm ...
0
votes
1answer
56 views

Thermodynamic statements [closed]

Question 13 from [1, p. 4.2]: Which of the following statements is true? (a) An ideal gas always obeys the equation: $PV^γ = \mathrm{constant}$ in adiabatic process. (b) An ideal gas ...
2
votes
3answers
88 views

Is enthalpy of combustion the 'heat released' or 'enthalpy change'?

In a constant volume calorimeter, $\pu{3.5 g}$ of a gas with molar weight $\pu{28 g}$ was burnt in excess $\ce{O2}$ at $\pu{298 K}.$ Temperature of calorimeter increased from $298$ to $\pu{298.45 K}$ ...
0
votes
1answer
29 views

Change in enthalpy equation [closed]

If the formula for change in enthalpy is ΔH=ΔU+pΔV, and ΔU = q - pΔV then shouldn't the formula be simplified to ΔH = q regardless of whether the volume or pressure is constant? Is this only true when ...
4
votes
1answer
89 views

Is it really possible for a liquid to stay afloat a gas (vapor)?

I have a book at home called Chemical Thermodynamics for Process Simulation (I have the first edition) and at the very beginning of chapter 2 of the book one may read the following: No reference is ...
1
vote
2answers
75 views

Work done in cyclic process [closed]

I have been told that when ∆V=0, work done will be zero (W=0). I know that, in cyclic process ∆V will be zero, since it's a path function and |W| i.e. magnitude of work done will be the area enclosed ...
0
votes
1answer
66 views

Heat exchange in adiabatic process

I know my teacher told me that In adiabatic process there is no exchange for heat between system and surrounding. Then he came to point. From first law of thermodynamics $$∆U = q + W \tag{1}$$ ...
-1
votes
1answer
23 views

Why Gibbs energy change of a process can be negative at constant temperature and pressure? [closed]

This question has been asked before, but the answers are not clear and satisfactory. If the pressure and the temperature are constant then G would be always zero. How would then G have a value other ...
0
votes
1answer
49 views

Irreversible Adiabatic Process [closed]

While studying about the entropy change of surroundings in irreversible adiabatic process, I came across a sentence. For infinite reservoir, all processes are considered reversible And suddenly ...
0
votes
1answer
43 views

qualitatively: Why are thioesters more reactive than regular esters? [duplicate]

In ochem students are taught that shorter bonds (like alkynes) have more energy than longer bonds such as alkanes. However in biochem we are taught that thioesters are very energetic bonds and release ...
5
votes
1answer
225 views

What is the true meaning of Gibbs energy and chemical potential?

After doing some research and reading I found some problems which I will try to state as clearly as possible. The definition of Gibbs Free Energy says "the greatest amount of mechanical work which ...
4
votes
0answers
57 views

Is pH in a charged hydrogel and its supernatant solution constant?

Let us assume we deal with ideal systems without interactions. The gel phase and the supernatant solution phase are in thermodynamic equilibrium. The supernatant solution shall consist of different ...
7
votes
0answers
111 views

Why are IUPAC's definitions of exo- and endothermic disconnected from the direction of heat flow?

I'm wondering if anyone can provide a rationale for IUPAC's definitions of exothermic and endothermic, since they disconnect these terms from the direction of heat flow. Specifically, here are IUPAC'...
-1
votes
1answer
53 views

Equilibrium pressure

Ammonium carbamate dissociates as follows: $$\ce{NH2COONH4(s)<=> 2NH3(g) + CO2(g)}$$ The value of $K_p$ for this reaction is found to be equal to $\pu{2.92 \times 10^-5 atm^3}$. If ...
1
vote
1answer
44 views

What are D_b and D_a in the Generalized Fugacity Coefficients table?

I've been referring the book: Chemical Process Principles: Part-II Thermodynamics. I found a table that gives me fugacity coefficients in a tabular form corresponding to various reduced pressures and ...
-1
votes
1answer
26 views

Bond energy and enthalpy of formation

Is the following equation true? $$\ce{∆_fH} = \ce{∆_{BE_{reactants}}H} - \ce{∆_{BE_{products}}H}$$ where $BE$ stands for Bond energy and $f$ stands for formation. I read that, $$\ce{∆_fH} = \ce{∆_{...
2
votes
1answer
51 views

Can someone walk me through this gas mixture question?

Argon $(\ce{Ar})$ and helium $(\ce{He})$ are initially in separate compartments of a container at $\pu{25 °C}.$ The $\ce{Ar}$ in compartment A which has a volume $V_\ce{A}$ of $\pu{9.00 L}$ and a ...
3
votes
1answer
115 views

Isothermal vs adiabatic compression of an ideal gas [closed]

Could someone please explain these specific questions physically (especially the first question!)? I understand the corresponding mathematical proofs, but not the physical reasoning? I have looked ...
0
votes
1answer
65 views

Enthalpy and heat relationship

They say that enthalpy of reaction is the heat when at constant temperature and pressure. So if enthalpy is $$\mathrm dH = \mathrm dU + p\,\mathrm dV = T\,\mathrm dS - p\,\mathrm dV + p\,\mathrm dV + ...
2
votes
3answers
103 views

Genuine confusion about the equilibrium constant [closed]

I gather that the equilibrium constant K = 1 implies that, at equilibrium, neither the forward nor the backward reactions are thermodynamically favoured. But if pressure of the system increases and ...
-1
votes
1answer
62 views

Enthalpy change of water [closed]

A given amount of (liquid) water in an open vessel is heated from 20 degree celsius to 50 degree celsius. Suppose it absorbs x joule in the process. What is the enthalpy change in the process? Is it = ...
0
votes
0answers
58 views

Standard state conditions in thermodynamics

Standard state conditions for standard Gibbs energy change stipulate (among other conditions) that partial pressure of each gas = 1 bar. e.g. 2A + 3B = 4C + 5D (all gases) Then for standard Gibbs ...
3
votes
1answer
111 views

Mathematical justification for Le Chatelier's principle

At equilibrium $$ \begin{align} K &= \exp\left(\cfrac{TΔS^\circ - ΔH^\circ}{RT}\right)\\ ⇒ \frac{\mathrm d \ln K}{\mathrm dT} &= \frac{ΔH^\circ}{RT^2} \end{align} $$ If enthalpy change is ...
1
vote
1answer
116 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
102 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
86 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'...
1
vote
1answer
215 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+}]}{...
0
votes
0answers
32 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
1answer
79 views

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

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 ...
2
votes
2answers
92 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 ...
1
vote
2answers
44 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
vote
4answers
81 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
43 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
49 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? ...
1
vote
0answers
141 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
0answers
41 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 ...
0
votes
3answers
2k 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
43 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
106 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
108 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 ...
0
votes
1answer
231 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 ...
3
votes
1answer
247 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 ...

1 2 3 4 5 38