What is the effect of decomposing one mole of gas on temperature?

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Discussion Overview

The discussion revolves around the effects of decomposing one mole of gas into two new molecules on temperature and pressure. Participants explore theoretical implications, energy conservation, and the nature of the decomposition process, considering various constraints and conditions.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • One participant suggests that if one mole of gas decomposes into two molecules with negligible energy required for the process, the pressure should increase due to the increase in the amount of matter, but questions what happens to the temperature.
  • Another participant argues that if the new molecules have the same mass, the temperature should be halved because the kinetic energy is divided between the two molecules, implying that temperature is proportional to kinetic energy.
  • A similar viewpoint is reiterated by another participant, emphasizing that energy conservation leads to a decrease in temperature while pressure remains unchanged.
  • One participant introduces the idea that the outcome depends on the process and constraints, noting that different methods of decomposition (e.g., heating slowly or increasing volume) can lead to varying effects on temperature and pressure.
  • Another participant mentions the implications of entropy change and enthalpy components in the reaction, suggesting that these factors also play a role in understanding the temperature and pressure changes.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between temperature and pressure following the decomposition of gas. There is no consensus on whether temperature increases, decreases, or remains the same, and the discussion remains unresolved with multiple competing perspectives.

Contextual Notes

Participants highlight the importance of the decomposition process and its constraints, such as whether energy is conserved or if the reaction is endothermic. The discussion also touches on entropy and enthalpy considerations, which are not fully resolved.

Ahmed Abdullah
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One mole of certain gas is confined in a container. Suppose every molecule has decomposed and given rise to- two new molecules. Let's assume (for this purpose ) it requires negligible amount of energy for the molecule to decompose (or not any energy at all). So what will we observe?
The amount of matter has been doubled by the process, so pressure should increase- that's obvious. What happens to the temperature?
Does it stay the same OR increase?
 
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I think I have got it. If the two newly formed molecules have the same mass then the pressure should not increase rather the temperature is halved. It is because temperature is something proportional to kinetic energy. . When a molecule is splitted to two new similliar molecule then the energy is divided between them each having halve of the original (energy is conserved). So temperature falls nothing happens to pressure.
Am I right? Please help.
 
Ahmed Abdullah said:
I think I have got it. If the two newly formed molecules have the same mass then the pressure should not increase rather the temperature is halved. It is because temperature is something proportional to kinetic energy. . When a molecule is splitted to two new similliar molecule then the energy is divided between them each having halve of the original (energy is conserved). So temperature falls nothing happens to pressure.
Am I right? Please help.
I would say yes.
 
It depends on the process and what the constraints are. You have an endothermic reaction that increases the number of moles of gas. You can:

- Decompose by heating slowly, which increases pressure at constant temperature
- Decompose by increasing volume slowly, which decreases temperature at constant pressure
- Combine activities or conduct the process irreversibly, which could result in a combination of changing temperature and pressure.
 
Ahmed Abdullah said:
One mole of certain gas is confined in a container. Suppose every molecule has decomposed and given rise to- two new molecules. Let's assume (for this purpose ) it requires negligible amount of energy for the molecule to decompose (or not any energy at all). So what will we observe?
The amount of matter has been doubled by the process, so pressure should increase- that's obvious. What happens to the temperature?
Does it stay the same OR increase?

The total number of moles changes and you have an entropy change if you can recall there's an equation S=Q/T

Also note that such a reaction is going to have an enthalpy component due to the changes in bonds.
 

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