Does a molecule want a geometry that has high energy of low energy

That depends on what you mean by "high energy molecules" If you are referring to molecules that release a lot of energy upon a chemical reaction, then butane with the formula C4H10 is a random example. Butane releases a good chunk of energy upon combustion, methane and other C-H molecules are similar, but those are just examples, there are TONS. 

You could also be referring to molecules which give a lot of energy to the body during organic processes. These are sugars and carbohydrates. An example would be glucose, with the formula C6H12O6. 

Combination reaction: joining of two different substances to form a more complex substance.decomposition reaction: breaking of a compound into two or more products.  i hope this !