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.
2,178
questions
-1
votes
1answer
23 views
Why does water splash if you put it into a hot pan?
I had kept my tea pan on the stove (At high)for about 30seconds . I was making tea and getting the water to put in the tea pan. There was nothing in it before that .After that , I quickly poured some ...
0
votes
0answers
13 views
Calorimetry Question - determine temperature change without knowing enthalpy change?
I have a lab that I honestly cannot figure out.
Basically, we have a video where we watch 200 ml of NaOH (2M) and HCl (1M) combined in a calorimeter with a magnetic mixer. Pretty standard. This video ...
0
votes
1answer
46 views
Free Expansion - Ideal Gas vs Real Gas
By free expansion, I am referring to gas kept in a piston-cylinder arrangement freely allowed to expand against vacuum.
It is clear to me that free expansion is an irreversible process because if it ...
0
votes
0answers
25 views
Calculating change in Gibbs Free Energy for a specific type of problem
Can anyone describe what is going on here?
$$Si(liq.)=Si_{(1 weight percentFe)}$$
I have come across this statement quite a few times in Metallurgical Thermodynamics.All that they ask for is change in ...
-1
votes
0answers
30 views
What is the difference between Electron Affinity and Electron gain enthalpy?
What is the difference between Electron Affinity and Electron Gain Enthalpy?
I have read on an unreliable resource that Electron Affinity is the amount of energy provided to the surroundings, and the ...
2
votes
1answer
30 views
Why is Specific heat of Ammonia higher than water?
The specific heat of water is lower than that of $\ce{NH3}$, but why?
$\ce{H2O}$ forms more hydrogen bonds if I am right, besides there's more electronegativity for Oxygen.
But still, $\ce{NH3}$ has ...
1
vote
0answers
22 views
Would the initial step of this mechanism be exothermic or endothermic? (Protonation)
My understanding is that since an O-H bond is being formed, the protonation step must be exothermic because energy is released upon bond formation. However, if I were to draw an energy/reaction ...
1
vote
1answer
51 views
Activation energy and degrees of freedom
According to the Arrhenius equation the rate of a reaction increases as at higher temperature a greater percentage of molecules have translational kinetic energy greater than or equal to activation ...
0
votes
1answer
39 views
How are these three things equal?
In this answer, I don't understand how this step worked.
Using $\mu_i = \mu^\circ_i + RT\ln \frac{P_i}{\pu{1 bar}}$
\begin{align}
\Delta G &= (c\mu^\circ_\ce{C} + d\mu^\circ_\ce{D} - a\mu^\circ_\...
2
votes
0answers
23 views
Verify heat produced by flame using enthalpy of fomation
I'm simulating using a CFD solver a pure oxygen/methane flame. However, I doubt that the combustion model does not produce enough heat. The heat from reaction is defined by $S_h=-\sum_{j} \frac{h_j^0}{...
1
vote
1answer
34 views
Can we dissolve salts with higher lattice enthalpy by providing heat?
It is well-known that
A salt with a higher lattice energy will not dissolve at all, because then $\Delta_{\text{sol}}H^\ominus$ will be negative.
So, the reaction should be endothermic, right? My ...
0
votes
0answers
37 views
Partial derivative problems [closed]
If I wanted to derive the partial derivative of a certain thermodynamic property. Can I make the assumption that the other thermodynamic property is constant although it does not present in the ...
3
votes
1answer
49 views
Calculation of Gibbs free energy of a chemical reaction
So, I'm trying to derive the equation: $$\Delta G = \Delta G^o + RT \ln Q\tag{1}$$
And trying to follow the steps detailed on this website here. I am having trouble deriving equation 7, which tries to ...
0
votes
0answers
15 views
Where can I find literature values for standard molar enthalpies of neutralization?
I'm looking for enthalpy of neutralization literature values for inorganic weak acids. NIST, PubChem, etc. don't list them. Is there somewhere else I should look?
-3
votes
0answers
28 views
Energy is required to heat ice
How much energy is required to heat 9 ice cubes each with a mass of $\pu{44.7 g}$ from $\pu{-26.3 Ā°C}$ to $\pu{-17.0 Ā°C}?$
I used the formula $Q = mc\Delta T.$
$$\pu{-17.0 Ā°C} - (\pu{-26.3 Ā°C}) = \pu{...
4
votes
3answers
107 views
Work done in expanding a gas reversibly and irreversibly
So, my chemistry teacher gave the class following $P_{external}$ versus $Volume$ diagrams for reversible and irreversible expansion of a gas which are as follows.
(Reversible expansion)
(...
3
votes
1answer
131 views
Why is the boiling point of sugarcane juice lower than the boiling point of water?
As the boiling point is a colligative property, one would expect that the boiling point of sugarcane juice should be higher than pure water because Sugarcane juice contains water (75ā85%), non-...
2
votes
1answer
57 views
Entropy change during irreversible process
Entropy change is defined as $\Delta S = \int \frac{\delta Q_{rev}}{T} $, where $Q_{rev}$ is heat transferred through a reversible process. Iām a little confused how this works, so I have a couple of ...
7
votes
0answers
64 views
Why does entropy increase in reactions that make more molecules?
I used to understand this (more molecules ā more degrees of freedom), but do no longer, because the total number of atoms is conserved, so translational d.o.f. should just be turned into internal d.o....
1
vote
1answer
31 views
Question regarding $Z$ (Compressibility factor)
Oh! This problem has been bugging me for a long time. According to Wikipedia, the Compressibility factor $Z$ is defined as the ratio of the volume occupied by a real gas to the volume occupied by an ...
-1
votes
0answers
26 views
Small ring's orbital characters
small rings have more p character in the ring and more s character outside the ring
Is there any explanation? I don't understand why small rings have more p character in the ring and more s character ...
14
votes
5answers
1k views
Is light a reactant in photochemical reactions?
According to IUPAC a photochemical reaction is a reaction caused by absorption of light. I still can't understand how we should consider light as a part of a reaction. Is a catalyst or a reactant?
In ...
0
votes
1answer
33 views
What is change in internal energy of a system in which combustion occurs at constant temperature?
We got a question in a test, in which we were asked which system has zero change in internal energy and it had an option which was combustion of methane at constant temperature. I imagined this to be ...
1
vote
0answers
76 views
What causes little spikes in a flame? [closed]
I have a lighter at home which everytime I use it, generates little spikes (see picture below) which eventually disappear.
The Spikes are not an effect generated by the camera. I can confirm that ...
1
vote
1answer
31 views
Confusion in calculating $\Delta U$ from a bomb calorimeter
In the book, it is mentioned the formula for $\Delta U$ in a bomb calorimeter without any derivation:
$$\Delta U = q_v = \frac{Q\times M\times \Delta T}{m}$$
where
$$Q=\textrm{heat capacity of ...
3
votes
0answers
70 views
A thermodynamics problem with an interesting equilibrium condition
Usually, when we analyze reactions, we assume that the reaction takes place at constant pressure or at constant volume. But there is no reason to assume this is generally the case, and so my friend ...
2
votes
0answers
31 views
Hampson-Linde cycle: why does expansion need to be isenthalpic
If I understand correctly, the fluid in the Hampson-Linde cycle goes through an isenthalpic (basically a free?) expansion. For ideal gases, T would remain the same. But, depending on the substance and ...
2
votes
0answers
26 views
What favors the active transport in a membrane?
I was reading about active transport in membranes where ATP is used. ATP "reacts" with the protein pump and converts into ADP and also make a conformational change to the pump. Now this ...
1
vote
0answers
32 views
Why does sodium carbonate heat up when mixed with water? [closed]
I have a sample of sodium carbonate anhydrous (from heating sodium bicarbonate above 100c). When I mix in water, it heats up. Why does this happen? Where is the energy coming from? What form is the ...
4
votes
1answer
34 views
When to include the mass of the dissolved substance in calorimetry problems?
In some calorimetry problems, in which a substance is dissolved in water and we want the heat of the reaction, the mass of the dissolved substance is included in the mass plugged into mcat but other ...
-1
votes
1answer
87 views
Are all exothermic reactions necessarily spontaneous? [closed]
I was told that the statement "all exothermic reactions have negative free energy change" is false.
But I learnt Gibbs free energy as the "energy stored inside a system capable of doing ...
1
vote
0answers
29 views
when is a system of mass-action reactions guaranteed to satisfy detailed balance?
when does a system of mass-action reactions satisfy detailed balance for any non-zero choice of the rate constants?
consider a trivial example:
$X + Y \ce{<-->[k1][k2]} XY$
satisfies detailed ...
0
votes
1answer
52 views
A lot of confusion in 1st law of thermodynamics [closed]
My sir told me that Total energy of system = K.E + P.E in starting.
Then Change in energy = F(External force on body ) * displacement of walls.
Then from here , change in energy = W+q.
(Donāt ...
1
vote
0answers
24 views
Help in understanding first way of changing the state of system
There is a statement in my book:
THERMODYNAMICS
One way: We do some mechanical work, say $\pu{1 kJ},$ by rotating a set of small paddles and thereby churning water. Let the new state be called $\...
-2
votes
0answers
20 views
What is the standard state for a solid, liquid, gas and a solute?
I am getting very confused about the standard state of a substance. Some definitions says that standard state for a gas is when gas is at 1atm pressure, some says it is when it's fugacity is unity. ...
-1
votes
1answer
35 views
What is the implication of having the internal energy equal the Gibbs free energy?
I came up with a hypothetical equation of state, where one of the consequences is that $U=G$, where $U$ is the internal energy and $G$ is the Gibbs free energy. I wanted to ask the chemists, is there ...
-1
votes
0answers
17 views
How can we tell if a substitution reaction will be thermodynamically favoured
My understadning was like in the case of a cyclohexane we would see a thermodynamically favoured reaction if an axial substituent became equitorial in the case of a inverted Sn2 reaction but I would ...
0
votes
1answer
43 views
How to calculate ārGº from entropy and āfGº in different temperatures? [closed]
"The total oxidation of glucose occurs according to the following chemical equation:
C6H12O6 (s) + 6O2 (g) -> 6CO2 (g) + 6H2O (l)
The following table gives us the free energies of standard ...
1
vote
0answers
42 views
Is it possible to have three stable liquid phases in a binary mixture?
With this system, it would be possible to have three liquid phases and two liquid-liquid coexistence regions at various compositions. Similar behaviour is common for solids such as alloys, sometimes ...
-1
votes
1answer
39 views
Change of entropy of a thermal reservoir [closed]
How to calculate/derive the change in entropy of a heat reservoir as function of its internal energy? If the constant temperature of heat reservoir is T, and
$$ S(U_0)=S_0,$$
what is $$ S(U)? $$
3
votes
0answers
90 views
(Probabilistic) entropy associated with many equally probable microstates
This is a pretty naive question. The probabilistic definition of entropy is (for a mole of particles)
$$-R\sum_i p_i\ln p_i $$ in which $p_i$ is the probability of a given microstate and $\sum p_i =1, ...
1
vote
0answers
40 views
Gibbs free energy as a difference of irreversible and reversible heats
I read in a book that āG=āH-TāS and then āH and TāS were substituted with Q and Qrev respectively(where Q and Qrev are heats added to the system in any process and reversible process respectively) and ...
2
votes
0answers
49 views
Why does the plot of volume and temperature have a kink in a second order phase transition?
The $(b)$ part of the figure shows how thermodynamic variables change in a second order phase transformation.
We observe there is a kink in the plot of volume with temperature.
Why is that so?
The ...
1
vote
1answer
38 views
Enthalpy of mixing of a non-ideal solution [closed]
I have this equation of FloryāHuggins model:
$$\Delta_\mathrm{mix}G = RT(n_1\ln\phi_1 + n_2\ln\phi_2) + \chi n_1\phi_2,$$
where $\phi$ is the volume fraction, $n$ is the amount of substance and $\chi$ ...
0
votes
1answer
36 views
Why is adiabatic process isentropic?
Adiabatic process is isentropic, but I can't get it why is it so. If we go by statistical method
$$S = K\ln W,$$
where $W$ is the thermodynamic probability, and if we look into adiabatic expansion the ...
1
vote
1answer
35 views
Work done by system of ideal gas in isobaric expansion
Consider a system of ideal gas in a container with piston and the isobaric expansion of gas takes place.
As the process is isobaric, so initially the pressure of gas is equal to atmospheric pressure ...
1
vote
1answer
67 views
Finding work done for a chemical reaction at non-constant pressure and temperature
I have studied the expression for work done for a chemical reaction which is basically $W=-\Delta n_{g}RT$. Along with this, the assumption that has been made is that chemical reactions take place at ...
0
votes
0answers
21 views
Why can the standard enthalpy of formation be calculated for different states of matter when the temperature should be constant?
If the standard enthalpy of formation needs to be determined at $25ĀŗC$ and 1 atm of pressure then why is it possible for the enthalpy of formation to be calculated for the liquid, solid, and/or gas ...
-1
votes
1answer
45 views
Water Gas Shift Reaction [closed]
Considering the water-gas shift reaction
$$\ce{CO(g) + H2O(g) <=> CO2(g) + H2(g)},$$
I would like to understand how evolves $K^\circ$ the equilibrium constant of this reaction when I add water ...
2
votes
1answer
56 views
Exergonic vs Endergonic Reactions
Problem
Problem 3, concept check 8.2 from Campbell Biology [1, p. 150]:
Some partygoers wear glow-in-the-dark necklaces that start glowing once they are āactivatedā by snapping the necklace. This ...
