chem destroyer question

[TimeforDAT]

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on gchem number 75, the explanation doesn't make sense. how is it that when the temperature of the water goes down, the delta h is positive and that if it is an endothermic reaction shouldn't the solution feel cold??

 

[tinman831]

on gchem number 75, the explanation doesn't make sense. how is it that when the temperature of the water goes down, the delta h is positive and that if it is an endothermic reaction shouldn't the solution feel cold??

temperature of the water goes down = delta H is positive = endothermic = solution feels cold

 

[Nasem]

Now you got me confused lol
If temp of water is going down, it means, the water is giving away its "heat" there for the reaction is... exothermic... right ?? so Delta-H is negative

 

[bxs023100]

ok, the question says that the compound dissolves in water spontaneously, so we automatically know that delta G is < 0.

also, it says that it is dissolving in water. Going from solid to liquid ALWAYS has a positive delta H and S because more disorder is created.

it also says that the temperature of the water decreases. if the temp. decreases, it means that it is cold. so that means that it is endothermic because endothermic reactions are cold.

even if the cold = endothermic part doesnt make sense, memorize the fact that going from left to right on the phase diagram is positive delta H and S/
and going right to left is always negative delta H and S

 

[Danny289]

on gchem number 75, the explanation doesn't make sense. how is it that when the temperature of the water goes down, the delta h is positive and that if it is an endothermic reaction shouldn't the solution feel cold??

again concept!
get the concept! the whole problems come from that.
about disorder, there is not any problem . S>0
Spontaneous ====>G< 0
water becomes cold--------> loosing heat(energy)-------> the heat goes for reaction= the reaction need energy to start.
don't focus on water, water is nothing but (heat) donator for reaction that we need.

smart thinking: now you can think a little deeper. this reaction will not be happened in cold water!!!
hopes it helped

 

[artsyme]

on gchem number 75, the explanation doesn't make sense. how is it that when the temperature of the water goes down, the delta h is positive and that if it is an endothermic reaction shouldn't the solution feel cold??

This may not be a scientifically correct lab setup, but its the simplest way of picturing it:

Suppose you have a covered glass of water. The system then includes the water + the surrounding (air). If the temperature of the water has decreased, it is because the air has ABSORBED the water's heat, making the solution(water) feel cold. The heat is absorbed by the air making the reaction system hot, which is why it is endothermic. I hope this helps!