Endo vs. Exothermic

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504047082
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Endo vs. Exothermic

Postby 504047082 » Sun Dec 08, 2013 10:23 am

How can you tell if a reaction is endothermic or exothermic just from the reaction? I know that endo thermic requires heat to form bonds and exothermic releases heat when breaking bonds but I am having a difficult time recognizing this in the reaction. Also, what does delta Hr degrees mean?

ex. equation FeO + CO --><-- Fe + CO2

Chem_Mod
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Re: Endo vs. Exothermic

Postby Chem_Mod » Sun Dec 08, 2013 10:37 am

Usually, you will be given a delta H value. If delta H is positive, then you know it is an endothermic reaction. However, if delta H is negative, then you know it is exothermic. From looking at the practice exams, if no delta H is given, the question will usually state that the reaction is endothermic or exothermic.

Also, delta Hr degree means the standard delta H of the reaction, measured when every reactant is in its standard state (such as water as a liquid, oxygen as a gas...).

304579397
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Re: Endo vs. Exothermic

Postby 304579397 » Sun Nov 08, 2015 11:36 pm

Why does an exothermic reaction go backward to reach equilibrium?

Jacqueline Lee
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Re: Endo vs. Exothermic

Postby Jacqueline Lee » Wed Nov 11, 2015 9:53 am

If heat is applied to an exothermic reaction, the reaction will reach equilibrium by shifting to the left. How Dr. Lavelle explained it during lecture was that if a reaction loses energy to form products(reactants -> products), the reverse reaction would use up energy(products -> reactants).

In other words if the reaction is exothermic in one direction, it's endothermic in the other direction, which hints to us which side of the reaction will be favored in order to reach equilibrium when heat is applied.

Juskarun Cheema
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Re: Endo vs. Exothermic

Postby Juskarun Cheema » Sun Nov 15, 2015 12:16 am

Hi,

I have a question regarding these reactions. Is there a way to deduce endothermic vs. exothermic reactions if you're not given the change in heat value?

Thanks!

Laila Sathe 1D
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Re: Endo vs. Exothermic

Postby Laila Sathe 1D » Fri Nov 20, 2015 12:13 pm

I think there is, but for the purposes of this class we don't have to know that.

Nikhil Davuluri 2A
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Re: Endo vs. Exothermic

Postby Nikhil Davuluri 2A » Fri Nov 20, 2015 2:42 pm

I've seen some basic reactions on the homework that do not give the delta H value. For example 2Cl <---> Cl2. Just from this information we can deduce that the forward reaction is exothermic because the Cl molecules are binding and energy is produced when bonds are formed. Therefore, the reverse reaction is endothermic as it takes energy to break the Cl2 bond. For more complicated reactions the delta H would most likely be given.


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