Stack Exchange Network

Stack Exchange network consists of 174 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Visit Stack Exchange

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.

-1
votes
0answers
19 views

Endothermic Reaction between Ammonium Chloride and Water

Why is the reaction between Ammonium Chloride and water endothermic and what exactly is the reaction? I already know that Ammonium Chloride dissociates in water as water is a polar molecule, but does ...
1
vote
1answer
58 views

Why do gases coexist as liquid and vapour?

I have having difficulty in understanding the liquefaction of gases.In the graph of isotherms of $\ce{CO2}$ I cannot understand how can gas coexist as liquid and vapour under area of $\mathrm{XCEBY}$....
-1
votes
0answers
33 views

Is equilibrium ever possible in an open system?

I have read in a few places (Wikipedia, school textbook) that "An open system can never reach equilibrium." There is the argument that if one of the products of a reaction is gaseous, it may escape, ...
1
vote
2answers
53 views

Help understanding the pressure's effect on equilibrium and Le Chatelier's principle

So let's say we have a closed system in the following reaction: $\ce{N2O4 -> 2 NO2}$ The only way to increase the system's pressure without adding any mole of gas and keeping temperature constant ...
-1
votes
1answer
39 views

Why are combustion reactions spontaneous? [duplicate]

I learned that spontaneous reactions are reactions whose activation energies can already be overcome with the temperature they're already in. Since the temperature they're in already provides enough ...
0
votes
0answers
28 views

Thermodynamics of exo/endothermic reactions

Complete chemistry newbie here, hi. Sorry if I ask a stupid question, but I wonder what does exo/endothermic means from a thermodynamical point of view. Considering that temperature (a macrostate) ...
0
votes
0answers
30 views

Freezing water droplets with liquid nitrogen vapor

I have an idea for a device but I'm not sure about the thermodynamics. Would liquid nitrogen vapor (not liquid) be cold enough to instantly freeze a spray or mist of water? I know water freezes at 0 °...
-1
votes
0answers
13 views

Creating empty space by controlling energy [closed]

This question is for a fantasy book that I want to write but I like to use physics and chemistry as a base for magic. Can a person who can control energy (like move it from an object to another) ...
0
votes
1answer
45 views

Expansion work by a gas when pressure is not explicitly constant?

How is it possible to calculate the work done by a gas when pressure is not explicitly stated to be constant? The question states: Calculate $\Delta H$, $Q$, and $W$ when $1\ \mathrm{mol}$ of He ...
0
votes
1answer
42 views

Entropy change during flow of heat

If heat $Q$ flows from the surrounding nature temperature at $T_\text{surr}$ to the system at temperature $T_\text{system}$, then $$\Delta S_\text{total}=\frac{+Q}{T_\text{system}}+\frac{-Q}{T_\text{...
0
votes
1answer
32 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 ...
3
votes
1answer
81 views

Why does ozone have higher entropy than oxygen?

$$\ce{3O2(g) -> 2O3(g)} \qquad \Delta H^\circ (\pu{298 K}) = \pu{+142 kJ mol^-1}$$ Since the RHS of the equation contains less number of gaseous molecules, naturally I expected the $\Delta S$ to ...
3
votes
1answer
77 views

Why is the Kelvin Temperature Scale Based on the Triple Point of Water?

Why would the Kelvin temperature scale not just be based on the freezing point of water, which is only .01 degrees Celsius off from it? Is this just a more accurate way of measuring and quantifying ...
1
vote
1answer
48 views

How many watts would I need to get CO2 from 30 °C to 4000 °C in 1 hour

Scenario: After reading some articles on new sorts of ways to deal with $\ce{CO2}$ in the atmosphere, a question came to mind: If I had 100 kg of $\ce{CO2}$, and I would like to heat it up from 30 °C ...
0
votes
1answer
86 views

should charge balance be based on activities?

We have a fluid with $\pu{0.01 M}~\ce{HCl}$ and $\pu{0.02 M}~\ce{K2HPO4}$, so if we assume activity coefficients are $1$ throughout we can find pH as $6.800012$ and confirm that at that pH there is ...
0
votes
2answers
55 views

Doesn't the isothermal irreversible expansion/compression of an ideal gas law violate the ideal gas law? [closed]

Let's say a cylinder has some ideal gas. We use a piston to suddenly expand the gas in isothermal condition from $1\ \mathrm{atm}$, $20\ \mathrm L$ to $0.5\ \mathrm{atm}$, $50\ \mathrm L$. Since the ...
1
vote
1answer
36 views

Expression for fugacity coefficient derived from a pressure-explicite EOS

In the book, Thermodynamics for Process Simulation, the authors propose to derive an expression for the fugacity coefficient from a pressure-explicit equation of state, as an example among many others....
-1
votes
2answers
33 views

Is water vapour formation possible at -10 degree celcius?

Under any pressure conditions is it possible ? If not then is there no water vapour present in places where temperature drops to -10 degree celcius ?
0
votes
0answers
42 views

Is the concentration of water included in the acid disscociation constant? - Wikipedia confuses me

I refer to the following wikipedia article https://en.wikipedia.org/wiki/Acid_dissociation_constant Header paragraph: Equilibrium constant. First the equilibrium constant is given in terms of ...
1
vote
0answers
47 views

Gibbs Free Energy: Exothermic, low temperature & reduced system entropy - such reaction is spontaneous or not?

According to $\ce{\Delta G^\mathrm{o}= \Delta H^\mathrm{o} -T\Delta S^\mathrm{o}}$, if a reaction a) is exothermic, b) reduces system entropy, and c) the temperature is low, then it is spontaneous....
1
vote
2answers
44 views

Equilibrium for very small amounts of reactants

Is there any difference in the concept of equilibrium when it comes down to dealing with extremely small amounts of reactants? Say we have $$\ce{A + B <=> C + D}$$ and $K_c$ is $100,000$. If ...
-1
votes
2answers
67 views

Shouldn't all isothermal processes be adiabatic?

We know, $\mathrm{d}H = nC_p\mathrm{d}T$ which implies $\mathrm{d}H = f(\mathrm{d}T)$ using $\mathrm{d}H = \mathrm{d}U + \mathrm{d}PV$ and $\mathrm{d}q = \mathrm{d}U + \mathrm{d}w$ we get $\mathrm{d}...
1
vote
1answer
66 views

Excluded Volume in van Der Waals equation

I was just reading over the EOS topic when where I stumbled upon excluded volume. Although the pictorial representation of the hard sphere model clearly shows that the excluded volume is 4 times the ...
-1
votes
2answers
29 views

Thermochemistry: What is the difference between the calculation of bond enthalpy and Hess's Law

so I know that hess's law is a indirect way to find the heat of reaction using the known heat of reaction of 2+ thermochemical equation, thus the formula is delta heat of reaction = enthalpy of ...
0
votes
0answers
60 views

Molar Enthalpy change

A Gas ($C_{\mathrm m,V}=\frac52R$) behaving ideally was allowed to expand reversibly and adiabatically from 1 litre to 32 litres. Its intial temperature was 327 °C. The molar heat enthalpy change (in ...
1
vote
0answers
24 views

Limiting factor on Belousov-Zhabotinsky reaction

In the thin film Belousov-Zhabotinsky reactions (popular on Youtube/in chemistry demonstrations), concentric rings of different colors propagate across a petri dish for minutes to hours as the ...
1
vote
1answer
64 views

Change in internal energy for the heating and vaporisation of water

What is the value of change in internal energy at $\pu{1atm}$ in the process $$\ce{H2O(l,$323\ \mathrm K$)->H2O(g,$423\ \mathrm K$)}$$ given $C_{\mathrm m,V}(\ce{H2O,l})=\pu{75.0 J K^{-1} mol^{-1}...
0
votes
0answers
53 views

Reason for formation of bubbles at boiling point [duplicate]

As I understand it, boiling takes place when the saturated vapour pressure equals to the atmospheric pressure. But, why does the vapour pressure need to be equal to the atmospheric pressure for ...
-1
votes
2answers
41 views

Isothermal expansion and compression for n steps [closed]

In my book, the graph for isothermal expansion for 2 steps and n steps is shown as this I can't understand the graph for both compression and expansion. Why is external pressure changing in going ...
-2
votes
1answer
34 views

How is an equivalence of a state and path function possible? [duplicate]

At constant pressure,∆H=q Where ∆H=enthalpy q=energy transferred by heating ∆H doesn't depend on how we get from one state to another, but q does. How can they be equal in any case? Is ...
4
votes
1answer
92 views

“Proof” that the chemical potential is less than zero for irreversible material changes

From Levine's Physical Chemistry 6th edition: In a closed system, $\mathrm dG = -S\,\mathrm dT + V\,\mathrm dP$ not only applies to constant composition but also reversible changes in composition (...
0
votes
1answer
58 views

When is a reaction said to be under kinetic control, is it not easily reversible?

If we consider this reaction: Compound 1 + Compound 2 --> Compound 3 I understand that if a reaction is under kinetic control, the less stable (e.g. a mono-substituted diene) is formed and if the ...
0
votes
1answer
44 views

How to optimise battery usage on modern electronics?

What is the best way to use an external power bank with a modern smart phone or similar device if the goal is to get as much usage out of the combination? Premises: The devices has a battery of 2 Ah ...
0
votes
0answers
22 views

How to calculate the enthalpy of fusion at a different temperature?

The heat capacity of liquid iodine is $80.7$ $\ce{J*K^{-1}*mol^{-1}}$, and its enthalpy of vaporization is $41.96$ kJ $\ce{*mol^{-1}}$ at its boiling point ($184.3$ $\ce{^oC}$). Furthermore, the ...
3
votes
1answer
62 views

Are Cubic Equation of states applicable to Liquids?

I was just going through a graph of isotherm given by cubic equation of state and noticed that isotherms passes trough the subcooled liquid region. Are these equation applicable to liquids?
1
vote
0answers
31 views

Why fire spreads out, depending on burning substance, with different speed?

In Action movies, I have seen a couple of times that if flammable gases or liquids like benzene are ignited, the fire spreads out within fraction of a second and sometimes there is also an explosion. ...
1
vote
2answers
100 views

Is there a widespread error/contradiction on whether to use internal or external pressure in computing work done by an expanding gas?

I've been looking at some sample problems involving work done by gas in an irreversible expansion in a piston. They all say $W = P\Delta V$, but some of them say to use internal pressure for $P$, ...
4
votes
2answers
77 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
0answers
26 views

Is there a thermodynamic explanation for how a substance behaves based on its pKa and the solution’s pH?

If the pH of the solution is lower than the pKa of the compound, then the compound will be protonated, because pH is a measure of the concentration of protons, and low pH means a high proton ...
0
votes
0answers
25 views

Question regarding thermodynamic principles of metallurgy

According to NCERT (12), India: Why is the reduction of a metal oxide easier if the metal formed is in liquid state at the temperature of reduction? Answer: The entropy is higher if the ...
2
votes
0answers
54 views

What factors contribute in making a solution more endothermic?

For example, a solution between potassium nitrate and water is more endothermic than sodium nitrate in water. Can someone explain?
0
votes
2answers
52 views

Why is the oxidation of sulfur dioxide not termed as heat of formation of sulfur trioxide?

According to me, the following reaction's heat should be termed as heat of formation of sulfur trioxide: $$\ce{SO2 + 1/2 O2 -> SO3}$$ However, in my textbook, they have that given it is not the ...
2
votes
1answer
40 views

Double surface in the pressure temperature concentration curve for a binary mixture

In the 3 dimensional diagram given, when a constant pressure plane intersects with the double surface, it produces a looped curve without a maxima or minima. What is the double surface and how is the ...
0
votes
2answers
10 views

Why do some chemical reactions require many steps? [duplicate]

I was a college student of physics ten years ago, and recently started to learn biochemistry. I enjoy finding out that some familiar concepts in physics play important roles in biochemistry such as ...
0
votes
0answers
30 views

Is this the equation of state?

\begin{align} pn^{-\lambda} &= \text{constant} \tag1\label{eq:one}\\ pV^\lambda &= \text{constant} \tag{2, adiabatic equation} \label{eq:two}\\ n\left(\frac{l}{2}\right)\delta T &=...
3
votes
0answers
75 views

If dG is a state function, why do reversible and irreversible paths differ?

For a reversible process at constant T,P in a closed system with no non-expansion work dG = 0. For an irreversible process under the same conditions, dG < 0. Since dG is a state function I would ...
1
vote
2answers
79 views

Absolute entropy

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 ...
3
votes
1answer
39 views

Understanding elementary rate laws from a probability stand point

I am learning about chemical kinetics and dynamics and as I understand for a general chemical reaction $$\ce{aA + bB -> cC + dD} $$ whose reaction rate, r, can be described by an elementary rate ...
1
vote
1answer
24 views

Reaction direction change based on phase of reactants and products

I am curious specifically how the entropy of a reaction will change if the phases of the reactants and products at different conditions change. For instance, a reaction $$\ce{O2(g) + C(s) -> CO2(...
0
votes
1answer
27 views

Would the change in enthalpy change of chemical reaction in space be considered as change in internel enrgy?

The formula of enthalpy change is change in H = U + P*(change in V) In space since there is no air, thus atmospheric pressure = 0 , P= 0 , Pv = 0 , So will H = U ?