Enthalpy and Activation Energy

[User441]

Could you help me with this question, please? In an exothermic reaction: A- The activation energy depends on the energy released. B- Products energy is lower than reactants energy and that depends on tge activation energy. C- Products energy is lower than reactants energy and the activation energy has nothing to do with the difference between them.

[studiot]

This multiple choice question must be homework.

What have you done so far?

Can you at least identify any of the answers that are definitely wrong and say why?

[User441]

It's not a homework. It's a question from a previous exam, and I'm just practicing to see how well I'm studying. Anyway, I'm pretty sure it's C, because the other 2 are obviously wrong. Yet, many other classmates are convinced it's B, so I wanted to make sure.

[swansont]

An exothermic reaction releases energy, so how can the products' energy be lower than the reactants'?  (or is this a terminology issue and that's how things are defined, for reasons which escape me)

[studiot]

 

7 hours ago, User441 said:

It's not a homework. It's a question from a previous exam, and I'm just practicing to see how well I'm studying. Anyway, I'm pretty sure it's C, because the other 2 are obviously wrong. Yet, many other classmates are convinced it's B, so I wanted to make sure.

 

Ok you have corretly identified that answers A and B are incorrect since they link activation energy to the energy levels of products or reactants.

C is correct the activation energy is quite independent of these energy levels.
I see the reaction is stated to be exothermic, note this also applies to endothermic reactions.

You may also find the following of interest in the light of this comment.

1 hour ago, swansont said:

An exothermic reaction releases energy, so how can the products' energy be lower than the reactants'?  (or is this a terminology issue and that's how things are defined, for reasons which escape me)

This is a chemistry question and you should know that Chemists use a different sign convention from Physicists for the first Law of Thermodynamics.

Basically Chemists regards any form of energy out as negative and any form of energy in as positive.
This includes work.

So if the energy level of the products is lower than that of the reactions the energy equation gives

(E_products - E _reactants ) as being negative.

However the term 'exothermic reaction' refers specifically to the production of heat, not total energy ie not including other forms such as light, sound or work.
The clue is in the 'thermic'.

Similarly an endothermic reaction specifically consumes heat.