Finding Reaction with High Density, Reversible Process

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Discussion Overview

The discussion revolves around the search for a chemical reaction where the resulting product has a higher density than the reactants and can be easily reversed with minimal or no energy loss. Participants explore theoretical and practical aspects of such reactions, including conditions under which density changes occur and the challenges of reversibility.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant seeks a reaction that results in a product with higher density than the reactants and can be easily reversed.
  • Another participant asserts that chemical reactions do not produce mass and that density cannot change without altering volume, suggesting that reversing reactions is often problematic.
  • A participant proposes that if two chemicals are combined without changing volume, the resulting density could theoretically be higher, depending on the specific reaction.
  • Concerns are raised about the feasibility of easily reversing reactions with minimal energy loss, with references to the second law of thermodynamics.
  • Examples of reactions that produce gases from solids or liquids are mentioned, but these reactions are noted to be difficult to reverse.
  • One participant suggests that any spontaneous gas-phase reaction could meet the density requirement, but reversibility remains a challenge.
  • Another participant questions the possibility of achieving the desired density change in liquid-state reactions, emphasizing the different behaviors of gases and liquids.
  • Examples of reversible processes that increase density, such as melting ice or mixing alcohol with water, are provided, though the latter may complicate separation.
  • A participant mentions that reactions forming precipitates typically yield denser products that can be separated easily, indicating a common laboratory occurrence.

Areas of Agreement / Disagreement

Participants express differing views on the feasibility of achieving a reaction with the desired properties. While some examples of density-increasing reactions are discussed, there is no consensus on the existence of a reaction that meets all specified criteria of high density and easy reversibility.

Contextual Notes

Participants highlight limitations related to the assumptions of constant volume and pressure during reactions, as well as the complexities of achieving exact density changes and reversibility in practical scenarios.

anubodh
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Sir, i desperately want to know a reaction in which the resulting product has more density than the reactants and which can be reversed easily (prectically) with minimal or no loss of energy.Please reply.Thanks..
 
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Chemical reactions do not produce mass, if you don't change the volume (which is not part of the chemical reaction) you cannot change the density. Reversing reactions is often problematic, but that is a different issue. You can easily revert a physical change of the volume.
 
I know that mass remains conserved but what i am saying is that initially if we have a chemical of volume v in which we add another chemical of volume v1.When we add them the volume of the resulting product is same but the density of the product becomes twice of v.
 
Then you have to compress the volume from v+v1 to v. That is not part of chemistry.
 
There are plenty of reactions that lead to an increase in volume (namely those that involve solids and/or liquids reacting to produce gasses (e.g. the decomposition of sodium azide into sodium and nitrogen gas, which was used to inflate airbags in cars). However, many of these reactions are not so easy to reverse. Of course, once you start asking for reactions that can be easily reversed with minimal or no loss of energy, you begin straying into the realm of perpetual motion machines and breaking the second law of thermodynamics.
 
Technically any spontaneous reaction taking place in the gas phase, with stoichiometry described by

A + B → C

will do what you want with the density (final density being sum of densities of the reactants). For example phosgene synthesis (somehow at the moment I draw blank when it comes to safer examples):

CO + Cl2 → COCl2

Not that it will be easy to find one that will be reversible.
 
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thanks for your replies.
Now,instead of naming the reaction, just tell me that is such a reaction is possible in which the final density being sum of densities of the reactants (or little less than sum of both) provided both the reactants and products in liquid state.
 
Unlikely. Gas is a gas, liquid is a liquid, they behave differently.
 
The final density has to be the same as the sum of the densities of the reactants, if you don't change the volume during the reaction.

It looks like you are thinking of something specific. Can you give more details what you are looking for?
 
  • #10
mfb said:
Then you have to compress the volume from v+v1 to v. That is not part of chemistry.

What do you mean here? In most reactions, you work at fixed (namely ambient) pressure, so volume changes are natural in chemical reactions.
 
  • #11
Then you still have to get the temperature right, and make sure that nothing can escape from the reaction - in general, you won't get exactly v as result.
 
  • #12
I am still thinking that the answer to the original question is relatively easy. E.g. the density of water is higher than that of ice at 0 deg. so melting ice will increase density and is easily reversible.
A mixture of alcohol and water is also more dense than the mean of the pure liquids and easy to separate. Mixing concentrated H2SO4 with water even leads to an absolute decrease in volume at high solution although separating into components is less easy.
 
  • #13
I suppose any reaction in which there is a precipitate fits your bill. Almost by definition. When dissolved reactants react to form a solid product this is almost always denser than the solution, and can be separated by a simple laboratory centrifugation. Very common in laboratories.
 

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