Decomposition+R.Stacey

Decomposition

The next type of reaction is ** decompostion **. Decomposition is the opposite of synthesis, because in a decomposition reaction, a unique molecule breaks down into two or more of its parts. This can be well represented by the following equaiton: AB  ** → ** A+B  v  Decomposition reactions are also very easy to see because in a sentence, the word 'decomposes' is always in it.  v  Also, if you are looking at an equation, the compound is broken down on the right of the arrow. So, for instance, if you see: // Water decomposes to form hydrogen and oxygen by passing an electrical current through it. // 1) First we look at the words and find the element names and the product.  v  So you see Water, Hydrogen and Oxygen.  2) So then, we go back to the elements and find their symbols: So it would look like H20 ** → ** H + O 3) After you find this, you need to find the elements' charges so that you can begin to balance the equation.  v   We know that since Hydrogen is irregular, it wants either 2 valence electrons or zero. Also, when hydrogen is alone, it is diatomic, meaning it looks like this: H2  v   Oxygen is in group 16, so it will have a -2 charge. We also know that when Oxygen is alone, it is diatomic, meaning that it will have a 2 next to it: O2  v   So now we have H20  ** → ** H2 + O2  v   Now we need to balance the equation. When H2 and O2 combine, they have 2 of each compound.  v  So we would just write H20  ** → ** H2 + O2 right? ** NO ** we still need to balance it.  v  So if we know that on the right the elements are diatomic, then we know that on the left we need to have the same amount of stuff. Here, the left has 1 Oxygen, but the right has 2 Oxygen. So, we need to add a ‘2’ to the left.  v  ** BUT ** since it is a compound, that puts a ‘2’ in front of Hydrogen as well, which means we need both sides to have 4 Hydrogen.
 * SO **, now we see that we have: 2H20 ** → ** 2H2 + O2. now we are balanced with the same amount of ‘stuff’ on each side!

 In the above picture, an electric current is going through water and the bubbling shows the decomposition. Click here to get back to the Main Page!!!