Endo or Exothermic?

  • Thread starter kuahji
  • Start date
  • #1
394
2
I have the equation Mg(OH)2 (s) -> Mg2+ (aq) + 2 OH- (aq)

I started out with 20 drops of 1.0M MgCl2 in a well & 10 drops of .5M NaOH. Phenolphthalein was also added. When I heated the mixture, it became white, when it cooled it became pink. So, how can I tell if it was endo or exothermic? I want to say it was endothermic because it shifted to the reactant side when heated, but I'm not sure, almost doesn't seem right if you look at the original equation.
 

Answers and Replies

  • #2
44
0
It might be helpful to consider energy like a component in the reaction. Let me explain.

An exothermic reaction releases energy to its surroundings. Usually we write this as:

(reactants) <=> (products) delta-H < 0

However, it's often useful to think of it like this:

(reactants) <=> (products) + (energy)

So by Le Chatelier's principle, if you add energy (by heating) to an exothermic reaction, you should shift the equilibrium to the left, i.e. towards the reactant's side. Vice versa for an endothermic reaction, which shifts to the right, i.e., towards the product's side.

Do you now see the answer to your original question?
 
  • #3
394
2
Yes I do, thank for the explanation.
 

Related Threads on Endo or Exothermic?

Replies
3
Views
10K
  • Last Post
Replies
1
Views
7K
Replies
1
Views
4K
  • Last Post
Replies
5
Views
33K
Replies
2
Views
276
  • Last Post
Replies
4
Views
88K
Replies
1
Views
7K
  • Last Post
Replies
4
Views
5K
P
  • Last Post
Replies
1
Views
2K
Top