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Okay this has confused me for centuries.
Now I know Exothermic = Release heat. Gets warm.
Endothermic = Absorb heat. Gets cold.

My question is, if a substance releases heat (i.e. goes through an exothermic reaction), wouldn't it LOSE heat, and therefore become cold?
Similarly, if a substance absorbs heat (i.e. goes through an endothermic reaction), wouldn't it GAIN heat, and therefore become hot?

My teacher told me it doesn't have to do with the temperature of the substance itself, but the temperature of the surroundings/atmosphere around that substance.
Is this true?

Thanks in advance for explaining!

anhtimmy

Yes. If the surrounding is hotter than the object, then the object is undergoing an endothermic reaction. On the other hand, if the surrounding is colder, the object is undergoing an exothermic reaction.

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Wait ... isn't it the opposite?
If the surrounding is hot, it's exothermic... and if the surrounding is cold, it's endothermic?

I'm more confused now.

sharkbait_ha

You're teacher said the same thing mine did. The actual substance itself doesn't matter.

Exothermic reactions release their energy (heat) which is the reason why they make the surroundings feel warm. That's the reason why they feel warm, the energy that escaped during the reaction affects the surroundings.

Endothermic reactions absorb surrounding heat during the reaction, and the surroundings feel cooler because there is less energy in the form of heat surrounding.

I don't know if I helped you at all, because I think I just repeated what your teacher said...xD

anhtimmy

When something releases heat, it gets colder.
When something gains heat, it gets warmer.

Endothermic and Exothermic is determined by which direction the heat(energy) flows.
Remember homeostasis? Everything is trying to balance out.

Exothermic:
-the object gets colder
-the surroundings get warmer

Why? Because heat is moving from the inside out
that's why it feels hot when you touch it

Endothermic:
-the object gets hotter
-the surroundings get colder

Why? Because heat is moving from the outside in
that's why it feels cold when you touch it

lolcats4

Antihimmy's first reply is incorrect, but he has done a good job at explaining it the right way above.

anhtimmy

How is it incorrect? o_o

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Thanks sharkbait!

And anhtimmy.
The second one makes a lot of sense.

You were wrong on the first one because you said when the surroundings are hotter than the object it's ENDOthermic (it should be exo) ... and vice versa.

anhtimmy

No... when the surroundings are hotter, the object is absorbing heat. Which makes in ENDO. o_o

lolcats4

No, when the surroundings are hotter, the object is RELEASING heat!!!!!

Watson&Crick

Zeroth law of Thermodynamics:

Any system tends toward thermal equilibrium, meaning, all objects will have same temperature. That means what is hotter will lose heat, or transfer it to colder objects, HEATING up the colder objects so they reach same temperature.

Anhtimmy explanation looks right.

exothermic, means the heat content of the system/reactants decreases (loss of energy) therefore negative delta H. Where did the lost energy go=> as released heat to the surrounding. Energy is conserved.

opposite for exothermic.

anhtimmy

If the surrounding is hotter, the object is colder. To achieve equilbrium, the object would need to GAIN heat, meaning its ENDOTHERMIC!! >:O

I think you are referring to the surroundings getting hotter. Then I would agree its exothermic. But as you can see, my explanation states that the surroundings are hotter. Not getting hotter. :P

lolcats4

Yes, I missed the part where you said it was undergoing the reaction. In that case what you said was correct lol.

anhtimmy

You really made me doubt myself for 2 days. I was thinking, "How could I have mixed those two things when I was studying for Bio."