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.

1,776 questions
Filter by
Sorted by
Tagged with
759 views

Heat of combustion per mole and per kilogram

I need to calculate the heat of combustion per mole and per kilogram of complete combustion of, say, X. I write reaction : $\ce{X + O2 -> ... + Q}$ Find Q using Hess law Now, what do I do after ...
1k views

Which one really determines how people feel. Heat or temperature? [closed]

We use water to cool down some machines because water has high heat capacity, which means it takes more energy to increase 1 degree. Heat transfer occurs only when temperature is different. We cool ...
22k views

at constant volume why the change of enthalpy doesn't equal the change of heat

At constant pressure $p=\text{const.}$, change of internal energy equals heat subtract work(PV). So, $q=\Delta E - pV$. So is the the change of enthalpy. So we say at constant pressure, the change of ...
438 views

Proving RTln($a_i$) equal to non PV work done by system,where $a_i$ is activity

We know that chemical potential is defined as ${\mu}_i={\mu}_i^{standard}+RT\ln(a_i)$. Here $a_i$ is the activity of $i^\text{th}$ component of solution. In case of gases instead of $a_i$ it is $f_i$ (...
247 views

Mistake in Wikipedia article on fugacity?

The Wikipedia Article on Fugacity contains statement The contribution of nonideality to the chemical potential of a real gas is equal to RT ln $\phi$ Here $\phi$ is fugacity coefficient.I think ...
5k views

How much heat is gained/released based off of equation?

Using this equation, $\ce{CaCl2(s) -> Ca^{2+}(aq) + 2Cl^{-}(aq)}$ and $\Delta H = - 325.0 \; kJ$ If you have 15.0 grams of the solid, how much heat is released or gained in kilojoules?
26 views

Can energy savings be estimated from activation energy differences?

Imagine two companies X and Y. Both companies use very similar technical equipment to carry out a biotechnological process where a chemical reaction is catalyzed by an enzyme. Company X uses an enzyme ...
270 views

Difference between non-thermal and thermal ionized gases

Why or when does non-thermal plasma become thermal? How do we know before hand if the ion temperature will differ from the electron temperature, on what parameters does it depend - where is the ...
215 views

Change in pressure or volume of molten salt

I am doing a project in which I fill a cylinder with a volume of $636cm^2$ (made of stainless steel) with molten salt: 60% Sodium Nitrate ($NaNO_3$) and 40% Potassium Nitrate($KNO_3$). The container ...
341 views

Conceptualizing Multiple Equilibria

Take the reaction: $$(1) \; \ce{A + B <=>X + Y}, \; K_1=\frac{[X][Y]}{[A][B]}$$ Now assume that X isomerizes to Z according to: $$(2) \; \ce{X <=> Z}, \; K_2=\frac{[Z]}{[X]}$$ We can ...
812 views

What is the energy change of ethene reacting with hydrogen gas?

$\ce{CH2CH2(g) + H2(g) -> CH3CH3(g)}$ Using this table, source: http://www.kentchemistry.com/images/links/Kinetics/TB08_003.GIF ...
696 views

How to estimate the dielectric constant of a liquid?

Are there any approximate relationships between the (static) dielectric constant of a liquid and properties of the individual molecules? For example, suppose I know the polarizability and dipole ...
11k views

Azeotropes and separation by distillation?

I have just recently learnt the theory of fractional and normal distillations and the basics of maximum and minimum boiling azeotropes. Most books say that the components of the mixture forming an ...
226 views

Balancing chemical systems - searching and sorting preliminary information

I was hoping I could get help finding ways to sort information in the problem. What kind of information does "the conversion of toluene to benzene..." give us that is relevant towards solving the ...
2k views

Approximate time for pure water pH to equilibrate in open air?

I'm a complete non-chemist, so I don't know how to calculate this, or even what to google for (my searches yielded esoteric research papers). I'm doing some hobby experiments, and I'd like to know ...
57 views

How to trace an Energy Time diagram?

I'm looking for data to create a simple graph of an exothermic or endothermic reaction but can't find any. Could someone help me with some enough data to create a Energy(time) simple graph.
1k views

A chemistry approach to environmentally friendly yoga mats… NBR, NR, TPE, PER [closed]

I'm currently seeking your expertise while creating a line of environmentally friendly yoga mats, and I apologize in advance if any chemistry knowledge of mine has been absent since college and I lack ...
159 views

517 views

How do I determine the temperature at which a dissolved substance evaporates?

I would like to understand the temperature at which a substance will vaporize when dissolved in a liquid. I have researched this online for hours, but haven't found a conclusive answer. Is it the ...
778 views

Is it possible to make liquid nitrogen with a bottle of CO2 gas and a freezer?

I really want to make liquid nitrogen(or oxygen) without using dry ice, a specially made freezer, or other chemicals. I have a mixture of some sponges, rotten grass, sugar and water, which makes ...
12k views

Derivation of relationship between Gibbs free energy and electrochemical cell potential

Why is $\Delta G=-nFE?$ I don't understand what the motivation is behind this definition. Was it derived or just given? The textbook provides no justification for this equation. In fact, much of the ...
53 views

Hot and cool milk

Usually I have the habit of keeping the hot milk for a while, until it becomes cool. I have noticed many a times that, drinking it, after keeping for a while, gives the mixture of hot (relatively less ...
1k views

How do point defects in a crystal relate to Entropy?

I am interested in Non-Stoichiometry and how it relates to crystal structures; In particular I wish to learn about surfaces of metal oxides. I am aware that point defects in such crystals are a result ...
194 views

Can we have an adiabatic process in a sealed metal container?

Let us consider a non-isothermal process inside a metal container. If we somehow are able to make the temperatures on the inside and outside the system remain same throughout the process, can it be ...
2k views

Heat transfer dependence on temperature gradient?

Is the rate of heat transfer between two bodies brought into thermal contact dependent upon the different in temperature between them, assuming they each have the same mass? Imagine two bodies of ...
863 views

Equilibrium between R and S configuration?

We have learnt that the energy evel of both R and S optical isomer of a compoud is same, just as well the entropy of each isomer is also same. If we consider the conversion of R form of a compound to ...
5k views

Michael reaction or nucleophilic attack at the alpha carbon of an alpha-beta-unsaturated ketone?

What conditions promote a nucleophile to undergo the Michael reaction over the nucleophilic attack at the alpha carbon of the carbonyl group in an alpha-beta-unsaturated ketone? I'm looking for an ...
449 views

How is a reduction in the number of molecules associated with a decrease in Entropy?

How is a reduction in the number of molecules associated with a decrease in Entropy? For example, stoichiometric equations like $\ce{H2 + O -> H2O}$ are enthalpy driven if I am correct. But it also ...
175 views

Solvated solids

I have a very basic question concerning solvation. If a solid (solute) was dissolved in a liquid (solvent), is the solute still in the solid state? or does it convert into another state of matter when ...
173 views

Does all processes that consume energy from outside result in negative entropy change?

In any spontaneous process entropy increases.In biological systems disordered elements are converted into highly ordered tissues etc(-ve entropy change) which make up living organisms. But, it ...
3k views

Vertical lines in a Pourbaix Diagram

I know that because of the absence of the hydrogen ions in a reaction ($n_{H+} = 0$) , the correspondent E-ph line have to be horizental , but what exactly the types of reactions (if there is) that ...
1k views

Entropy and racemization?

The process of racemization of an optically compound is entropy driven and hence nature prefers a racemic mixture to an optically active one, which is consistent with the idea of the intuitive ...
5k views

Methane seems to dissolve more readily in cold water. Why?

When you are diluting air in the system and/or properly evacuating it, you must consider water temperature. Methane is completely dissolved in water at 42 degrees Fahrenheit (5.5 C) but can be ...
387 views

Thermodynamics behind Deliquescence?

The phenomenon of deliquescence wherein a water soluble substance absorbs water from atmosphere and dissolve in it forming a saturated solution, has thermodynamic roots. I have read the fact that the ...
664 views

Electrode potentials at interfaces?

My questions relates to the fundamental concept of electrochemistry, more specifically the electrode potentials. 1) First, why is there a potential difference at the interface of two phases? ...
277 views

Negative retention for chloride in hydrolysate filtration

I tried to fractionate proteins as a function of their size with an ultrafiltration membrane. I observed a higher concentration of chloride in my permeate than in my feed or retentate. The proteins do ...
3k views

Why doesn't diffusion take place between immiscible liquids?

If we take a test-tube of bromine and invert an upside-down test tube of air on top of it, it'll diffuse with the air, until the bromine is thoroughly 'mixed' with the air in both test tubes. But why ...
99 views

Would cooling of a battery using cooler affect its life time?

My smartphone gets over heated where I use mobile data for long period. Last day I found a cooler of an old cpu, the thing silver in colour to absorb heat(with eventually gives out heat as it has more ...
I know that raising the temperature in a reversible chemical reaction causes the equilibrium to shift to the endothermic side. I know that $\Delta G = \Delta H - T \Delta S$ but I don't know how to ...