Predict the products of these synthesis or decomposition reactions. Write a balanced chemical ...

NH3 + HCL -> NH4+ + Cl- [balanced]

In this example, HCl is a strong acids. Characteristic of strong acids is that they completely dissociate, so expect H and Cl to break up

K2O

I'm predicting a dissociation reaction, where potassium and oxygen break apart:

K2O -> 2K+ + O2- [balanced]

Mg(OH)2 + H2O -> Not sure...

I've never seen this reaction. I looked at some sample reactions with Mg(OH)2, but didn't find it either.

Example reactions include:

• Mg(OH)2 = MgO + H2O
• Mg(OH)2 + 2HCl = MgCl2 + 2H2O
• Mg(OH)2 + 2HNO3 = Mg(NO3)2 + 2H2O
• 2HBr + Mg(OH)2 = MgBr2 + 2H2O
• Mg(OH)2 + H2SO4 = MgSO4 + 2H2O
• MgCl2 + 2NaOH = Mg(OH)2↓ + 2NaCl
• Mg + 2H2O = Mg(OH)2↓ + H2
• Mg(NO3)2 + 2NaOH = 2NaNO3 + Mg(OH)2↓
• 2KOH + MgSO4 = Mg(OH)2↓ + K2SO4
• Mg(NO3)2 + 2KOH = Mg(OH)2↓ + 2KNO3

For NH3 + HCL I didn't understand how it became NH4 and for K2O  the answer was 2K2O -->4K  + O2, the textbook may be wrong so I'm not sure, and for Mg(OH)2 + H2O the answer was Mg(OH)2 + H2O + MgO wasn't sure how they got that.

Okay, HCl dissociates to H and Cl. The NH3 makes a bond with H, forming NH4+, while Cl- is left alone.

2K2O -> 4K+  + O2 -- Yes, that makes sense, I forgot oxygen is diatomic.


There's a plus (+) before and after H20? You sure that's written correctly?

Just after the h2O, I wrote the plus before by accident but the question is written Mg(OH)2 H2O +  and then the answer was written like Mg(OH)2 H2O + MgO

That makes complete sense, I thought it was:


Magnesium hydroxide breaks down into: Mg(OH)₂(s) ⇌ Mg²⁺(aq) + 2OH⁻(aq) ... When coupled with water, the Mg²⁺ reactions with the oxygen of water, forming MgO and a water molecule

Okay Thanks!

 For those type of questions, how would you know when to make a bond between the two elements, like for example one of my questions was CaCl2--> and the answer is CaCl2--> Ca + Cl2 whereas for K2o--> the answer was k2o--> k + o2

and also what is the lewis structure for k2o? I tried searching the solution but I never got an answer

Depends on their position in the period table.

Calcium is in the 2nd column from the left, so it has a charge of +2
Chlorine is in the 2nd column from the right, so it has a charge of -1.

So normally what you do is separate them like this:

CaCl2 -> Ca + Cl

However, chlorine is a diatomic molecule consisting of only two atoms. So chlorine HAS TO be written with a subscript of 2. Other naturally occurring diatomic molecules are: hydrogen, nitrogen, oxygen, fluorine, chlorine, bromine, and iodine. They all get the same treatment:

CaCl2 -> Ca + Cl2

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The same can be said about K2O.

First break it up:

K2O > K + O

Notice that oxygen needs to have a subscript of 2 because it's diatomic.

K2O > K + O2

Now you need to balance it:

2K2O > 4K + O2

oh okay I thought you had to Crisscross the charges, thank you for clarifying

For ionic compounds the lewis structures are drawn a little different, this tutorial explains:



Let me know if this helps

but for a question like zn + s--> you would have to involve the charges? and thanks for the video will consider it

Yes, this involves charges.

Zn is 2+
S is 2-

You do a criss-cross:

Zn2S2

Now because they both have 2, you can cancel them to:

ZnS (Zinc sulfide)