MgCl2 + NaOH: Endo or Exothermic?

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In summary, the conversation discusses a chemical reaction where 20 drops of 1.0M MgCl2 and 10 drops of 0.5M NaOH were mixed with phenolphthalein. When heated, the mixture turned white and when cooled, it turned pink. The question is whether the reaction is endothermic or exothermic. The expert explains that an exothermic reaction releases energy to its surroundings and shifts towards the reactant's side when heated, while an endothermic reaction shifts towards the product's side. Therefore, based on Le Chatelier's principle, the reaction in question is endothermic.
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kuahji
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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.
 
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  • #2
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
Yes I do, thank for the explanation.
 

Related to MgCl2 + NaOH: Endo or Exothermic?

1. What is the reaction between MgCl2 and NaOH?

The reaction between MgCl2 and NaOH is a double displacement reaction, where the two compounds exchange ions to form two new compounds: Mg(OH)2 and NaCl.

2. Is the reaction between MgCl2 and NaOH endothermic or exothermic?

The reaction between MgCl2 and NaOH is exothermic, meaning it releases heat. This is because the products of the reaction have lower energy than the reactants.

3. How can we determine if a reaction is endothermic or exothermic?

We can determine if a reaction is endothermic or exothermic by measuring the change in temperature of the reaction mixture. If the temperature increases, the reaction is exothermic. If the temperature decreases, the reaction is endothermic.

4. Why is the reaction between MgCl2 and NaOH exothermic?

The reaction between MgCl2 and NaOH is exothermic because the bond energy of the products (Mg(OH)2 and NaCl) is lower than the bond energy of the reactants (MgCl2 and NaOH). This difference in energy is released as heat.

5. Can the reaction between MgCl2 and NaOH be both endothermic and exothermic?

No, the reaction between MgCl2 and NaOH can only be either endothermic or exothermic. It cannot be both at the same time. The energy change of a reaction depends on the specific reactants and products involved.

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