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
3answers
132 views

Estimating the absolute entropy of water at room temperature

I thought it would be fun to get an idea of how enormously large $W$ in $S = k\ln W$ is. I'd specifically like to estimate this for a mole of water at $\pu{1 atm}$ and $\pu{298 K}$. To do this, I ...
2
votes
2answers
710 views

Entropy change of isothermal irreversible expansion of ideal gas [duplicate]

Two mole of an ideal gas is subjected to isothermal expansion from $\pu{2 atm}$ to $\pu{1 atm}$ at $\pu{300 K}$. Calculate entropy change of the system, surrounding and total, if the process is ...
0
votes
0answers
68 views

Adiabatic flame temperature of a blast furnace gas

Calculate the adiabatic flame temperature of combustion of a blast furnace gas analyzing $25\%$ $\ce{CO}$, $10\%$ $\ce{CO2}$, and rest nitrogen. Use theoretical amount of preheated air at $\pu{1000 °C}...
2
votes
3answers
94 views

Solubility of solids in liquids

How does crystallisation happen and why? I have been told that when a solid is dissolved in a liquid solvent, an equilibrium is set up between processes of dissolution and crystallisation. But if ...
1
vote
1answer
47 views

Quasi-static implies that T aprox equals Tsurr?

A few days ago I re-visited my undergraduate thermodynamics notes and (as you may have seen from the amount of questions I have been posting) I have encountered many difficulties that I overlooked at ...
1
vote
1answer
157 views

Work done in an irreversible process

I was given a problem to identify whether the given statement is true or false. And the statement was: "Consider an ideal gas which is expanded from $(P_{1},V_{1},T_{1})$ to $(P_{2},V_{2},T_{2}).$ ...
1
vote
1answer
93 views

Determine surface area of heat exchange tube

A heat exchanger is used to cool down a stream of $\pu{20 kg s-1}$ of water from $\pu{80 °C}$ to $\pu{60 °C}$. The cooling water enters at a rate of $\pu{12 kg s-1}$ and $\ce{20 °C}$. The overall heat ...
1
vote
1answer
44 views

When a piston cylinder system that evolves isothermally and quasistatically is irreversible?

Suppose we have two states: $\ce{A}$ and $\ce{B}$. Considering a quasi-static isothermal process of an ideal gas, (and another condition, that is $T = T_\mathrm{surr}$) that join those states. Then ...
3
votes
1answer
56 views

Equation for overall heat transfer coefficient

The heat flow (in $[\pu{J/s}]$) through the wall of a tube of length $L$ and inner radius $R_0$ is $$Q = (2πR_0L)U(T_{1\infty} - T_{2\infty}),$$ where $T_{1\infty}$ is the bulk temperature ...
2
votes
0answers
43 views

Existence of single ion activities

I have used Davies equation to find what I believed was single ion activities and multiplied them on concentrations to define the thermodynamic dissociation constants for any kind of buffer to find ...
2
votes
1answer
65 views

Freezing trend of water

In this experiment, I used a digital temperature probe to measure the freezing point of water and some other salt solutions. I was just wondering if there was any explanations for 1. The first ...
1
vote
2answers
95 views

Concept of enthalpy at a given temperature

In thermodynamics, we always quote a fixed temperature, whenever we mention enthalpy of a reaction. For instance, one can determine the enthalpy of combustion of methane at 25 °C. Now almost all ...
5
votes
1answer
360 views

Need some help proving the following statements in Thermodyamics?

So in my second year thermodynamics class we are currently talking about entropy and deriving its definition from the 1st law. $$\mathrm{d}q_{rev} = dU - dw_{rev}$$ $$= C_{V}(T)dT + PdV$$ $$= C_{V}(T)...
0
votes
1answer
68 views

How to determine if a mixing process is spontaneous at constant temperature but variable pressure

This is a conceptual question. Many times we work with the gibbs energy of mixing under conditions of constant temperature but not pressure. In a problem like this: Suppose that 2.0 mol H2 at 2.0 ...
1
vote
1answer
46 views

Will the motion of particles always increase with the rise of temperature?

I came across this following question while poring over my textbook. Predict the change in the motion of particles you would expect in the following if the temperature was increased: a) Solid b)...
1
vote
1answer
36 views

I am looking for any substance that would be unstable or dangerous when it is cooler or not on heat, and is stable when it is being boiled

I am a first responder and one of our protocols when entering any unknown lab environment is to turn off any burners. Most of the time, we try to not disturb the environment as much as possible so a ...
2
votes
2answers
178 views

Hydrogen vs neon in terms of entropy

I know that both molecular size and complexity increase overall entropy, but between the two I'm not sure which increases it more. Would 1 mole of hydrogen have the greater entropy because it is two ...
2
votes
1answer
144 views

Free energy of solvation and Henry's law constant

I am trying to calculate the free energy of solvation of $\ce{CO2}$ from its Henry's law constant. As given on Wikipedia, the dimensionless Henry's law constant is $0.83$. If I try to calculate $\...
2
votes
1answer
80 views

How are octet-rule models supported by thermodynamics and quantum theory? [closed]

I understand that the four quantum numbers dictate how many electrons can "fit in a shell," but I don't understand how gaining a full octet is particularly energetically favorable. The example of ...
1
vote
1answer
38 views

Thermodynamics at absolute temperature [closed]

Assume I have kept a single molecule in vacuum and in absolute zero (0 K) temperature. There is no energy left in the particle, and hence any type of motion is absent. Now, what happens when I ...
0
votes
1answer
149 views

Work done by gas in isothermal process [closed]

A $20\ \mathrm l$ steel cylinder containing $\ce{N2(g)}$ at $20\ \mathrm{atm}$ and $300\ \mathrm K$ is kept in a big jar containing air at $1\ \mathrm{atm}$ and $300\ \mathrm K$ and sealed. $\ce{N2(g)}...
10
votes
1answer
750 views

Why was a Plimsoll symbol chosen to indicate standard state?

Historically, the Plimsoll symbol (aka Plimsoll line) was created as hull mark that would serve as a ready indicator of whether a ship was overloaded and thus running too low in the water. It was ...
0
votes
1answer
162 views

Whats the difference between reversible process in thermodynamics and reversible chemical reactions?

We know that in thermodynamics, reversible process never occur since entropy should be conserved. However, in chemistry we do have a lot of reversed chemical reactions that forms reactants from ...
0
votes
4answers
358 views

Is the titration of sodium carbonate with hydrochloric acid temperature dependent?

I am a chemistry teacher in a Cambridge school. In one of the titrations of sodium carbonate with HCl, there was one question asked: On heating the sodium carbonate solution before doing the ...
2
votes
1answer
60 views

Impact of Pressure on equilibrium of Tin allotropes

The pressure at the bottom of the Mariana Trench in the Pacific Ocean is $1090$ bar. What temperature will the two allotropes of tin be at equilibrium? Assume that the molar volume, energy, and ...
-3
votes
1answer
287 views

What is the molar enthalpy of reaction

When 0.45 g of Zn is added to 50.0 ml of 0.95 M HCl solution, the solution inside the calorimeter heats up by 12 °C. What is the molar enthalpy of the reaction (in kJ/mol)? I know how to find the ...
2
votes
1answer
145 views

Calculating ΔH from bomb calorimetry

Suppose we carry out a reaction in a bomb calorimeter whose starting temperature is $298.15\ \mathrm K$. Here we assume $\Delta V$ is close enough to zero that we consider the process to be at ...
0
votes
1answer
64 views

Using Hess's law to find molar enthalpy of formation without an initial reaction [closed]

I'm having issues relating Hess's law to this question: The given chemical equation represent the combustion of ammonia and the combustion of hydrogen $$ \begin{align} \ce{4 NH3 + 3 O2 &-&...
0
votes
4answers
187 views

Adiabatic processes and the Ideal Gas Law [closed]

in my first year chemistry textbook it wrights that in adiabatic proccess when there is a system of canister filled with gas and a piston above(and wheights on it) if we let the piston move upward by ...
1
vote
3answers
54 views

Is it correct to say that “some degree of pollution is an inescapable consequence of the Second Law of Thermodynamics”?

The quote above is from ‘Enlightenment Now’ by Steven Pinker, I was just wondering if this was true or if it misrepresented the Second Law. The full quote below... ...some degree of pollution is ...
0
votes
2answers
88 views

dSsur, dS and dStotal relation

By definition, dS=dqrev/T. Based on my understanding, the subscript rev means that the dq is heat exchanged in a reversible pathway from a state i to another state f, regardless of the actual ...
1
vote
2answers
97 views

Does dissolving something in water change the specific heat of the solution?

I’m a little confused on this topic. If I have a solid that I dissolve in water and that undergoes an exothermic reaction, can I assume that the specific heat $c$ of the solution instantaneously after ...
0
votes
0answers
37 views

Calculating the amount of a product at the reaction equilibrium

$\ce{Cr2O3}$ can be reduced to the elements chromium with high temperature and carbon by this two reactions: $$ \begin{align} \ce{Cr2O3(s) + 3C(s) &-> 2Cr(s) + 3 CO(g)} \label{rxn:1}\tag{1}\\ \...
0
votes
1answer
30 views

Is there any difference between thermal energy at room temperature in fluids(water) vs air?

Context of the question: I was reading on hydrogen bonds, specifically how close they are to the thermal energy of the fluids. So I googled the value of thermal energy at room temperature, which was $\...
1
vote
1answer
176 views

Calculating temperature change of helium due to Joule-Thomson effect

We are trying to fill a rocket helium tank that is 78 liters with helium, final pressure of $\pu{10500 psi}$. We plan to pressurize high pressure tanks to $\pu{20000 psi}$ using a compressing pump ...
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^\...
2
votes
1answer
81 views

Reaction energy of oxygen and hydrogen

From the bonding energy of following bonds that I found in a Wikipedia article, I calculated the reaction energy that would be released when oxygen and hydrogen are reacted to produce water. The phase ...
2
votes
1answer
54 views

How is “the surrounding” and its temperature defined to calculate entropy change during a reaction?

Lets say supercooled liquid water at $263\ \mathrm K$ isobarically changes to solid ice at the same temperature. I wish to calculate the change in entropy of the surroundings and I happen to know the $...
0
votes
0answers
30 views

Deriving the entropy as a function of concentration

In a physical chemistry class, the professor derived entropy $S$ as a function of concentration starting from $S=k\ln(W)$. Somehow he made a mistake and ended up with the wrong sign. This remains ...
1
vote
2answers
108 views

Why enthalpy is defined at a constant pressure?

How absolute enthalpy and enthalpy change are defined? What is the clear difference between enthalpy and heat? Is it the constancy of pressure what makes the enthalpy a state function? My teacher ...
1
vote
1answer
471 views

adiabatic expansion vs Joule-Thomson Effect

Source: The1stLawofThermodynamicsLesson4 I am looking for difference between adiabatic expansion and Joule-Thomson effect. Looking at the setup demonstrating Joule-Thomson effect, I find no essential ...
0
votes
0answers
26 views

What drives the formation of salts?

Can someone explain why potassium and chlorine undergo an exothermic reactiom to form an ionic solid despite that potassium has an ionisation energy of 425 kJ mol-1 and chlorine has an electron ...
0
votes
2answers
79 views

Flow rate of the fuel consisting of ethanol and water burning in air of a given flow rate

I hope that someone could give me some hints or tips on how to approach this question, even though these types of questions are usually closed off as homework. A burner is run by a fuel mixture of $...
0
votes
0answers
36 views

Is it possible to convert a combustion reaction directly into an electrochemical one?

I'm fairly inexperienced in chemistry so forgive me if this question is silly but, why is it not possible to convert a combustion reaction to an electrochemical one directly and harvest the electrical ...
1
vote
1answer
238 views

Why are catabolic reactions exergonic and anabolic reactions endergonic?

Catabolism breaks apart large molecules and anabolism creates large molecules. Catabolism is supposed to be exergonic, while anabolism is supposed to be energonic. Id on't really understand this. By ...
1
vote
2answers
113 views

Why are reversible reactions spontaneous?

If a reversible chemical reaction is spontaneous in one direction, shouldn't it be non spontaneous $(ΔG > 0)$ in the other? In other words for the reaction: $$\ce{A + B ⇌ C + D}$$ if $$\ce{A + B ...
11
votes
1answer
691 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 $\ce{P=O}$ ...
1
vote
2answers
67 views

Exact meaning of constant volume heat capacity

From Wikipedia: $$ \left(\frac{\partial U}{\partial T}\right)_V = \left(\frac{\partial Q}{\partial T}\right)_V = C_V, $$ $C_V$ is what known to be constant volume heat capacity. I don't really get ...
1
vote
1answer
112 views

Is delta S the same in reversible and irreversible processes?

I've read that change in entropy of a system is the same for a system in reversible and irreversible processes since it is a state function and does not depend on the pathway. Does this only apply to ...
1
vote
1answer
58 views

Inexact differential-path function

From Wikipedia: an inexact differential cannot be expressed in terms of its antiderivative for the purpose of integral calculations What's the mathematical reason that inexact differential cannot ...