Why is cooling considered to slow reactions?

[scilearner]

Hello everyone

 

I'm just wondering why is cooling considered to slow reactions. I mean f you want condensation heating would slow the reaction. I like to know exactly how condensation occur at molecular level. I know when you heat gas it expands. So when you cool a gas does it contract, and where does the energy for change phase from gas to liquid come from. Does cooling provide energy too like heat. Why is that when cooling in this case there is not much kinetic energy but a reaction (condensation) takes place. Your help would much appreciated thanks!!

[hermanntrude]

condensation isn't a reaction. Condensation is a physical process.

 

When you cool a gas, there is less kinetic energy in the system, meaning that, on average, the molecules are moving slower. All molecules have an attraction for each other. In some molecules the attractions are larger than others, but there is always an attraction. When there is less energy available to the molecules, they are more likely to stick together and form a condensed phase (liquid or solid).

 

There is no energy associated with "cold" cold is simply a lack of heat and heat is thermal energy, related to kinetic energy.

 

Imagine you have a bag of weak magnets (imagine for a minute that they only attract each other, not repel). If you leave the bag alone the magnets will stick together. if you start moving the bag about a bit, the magnets might slide over each other, because you've given them some energy, but not enough to make them separate from each other. Now imagine you give the bag a really good shake. While the bag is shaking, the magnets will all fly around inside the bag, hardly sticking to each other at all. That's because the energy you're providing is a lot more than the energy of the attractions between them.

 

That's just a metaphor, not the real case, but it might help to understand.

[jdurg]

condensation isn't a reaction. Condensation is a physical process.

 

When you cool a gas, there is less kinetic energy in the system, meaning that, on average, the molecules are moving slower. All molecules have an attraction for each other. In some molecules the attractions are larger than others, but there is always an attraction. When there is less energy available to the molecules, they are more likely to stick together and form a condensed phase (liquid or solid).

 

There is no energy associated with "cold" cold is simply a lack of heat and heat is thermal energy, related to kinetic energy.

 

Imagine you have a bag of weak magnets (imagine for a minute that they only attract each other, not repel). If you leave the bag alone the magnets will stick together. if you start moving the bag about a bit, the magnets might slide over each other, because you've given them some energy, but not enough to make them separate from each other. Now imagine you give the bag a really good shake. While the bag is shaking, the magnets will all fly around inside the bag, hardly sticking to each other at all. That's because the energy you're providing is a lot more than the energy of the attractions between them.

 

That's just a metaphor, not the real case, but it might help to understand.

 

Good metaphor there! I think that explains condensation and "heat" quite well.

[UC]

Many reactions have an "activation energy" which is supplied by heat. This allows unstable, high-energy intermediates to form, which then collapse into a lower energy final product.

 

The colder a reaction mixture gets, the less the molecules move around and the less likely they are to run into the other reactant(s). This is why reactions are usually carried out in the liquid or gas phase. High mobility and easy mixing of the reactants. Solids would require providing intimate contact on a microscopic level, which can be realized for some reactions by grinding the reactants together.

[hermanntrude]

Good metaphor there! I think that explains condensation and "heat" quite well.

 

I have to say i was quite pleased with it myself