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

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In a scenario where one mole of gas decomposes into two molecules with negligible energy input, the amount of matter doubles, leading to an expected increase in pressure. However, the temperature response is debated. If the new molecules have the same mass as the original, it is suggested that the temperature could decrease, as the kinetic energy is divided between the two molecules, resulting in each having half the original energy. This implies that temperature, which is proportional to kinetic energy, would fall while pressure remains unchanged. Further discussion highlights that the outcome depends on the specifics of the decomposition process. For instance, if the decomposition is endothermic and occurs under different constraints—such as heating slowly or changing volume—this could lead to variations in both temperature and pressure. Additionally, the process involves changes in entropy and enthalpy due to bond alterations, indicating that the thermodynamic behavior is complex and context-dependent.
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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