When 'The big bang' happened lots of large pieces of molten rock was flying around the solar system. As the rocks crashed together they got bigger and as the got bigger they attracted more rocks. Some scientists think that a large piece of molten rock hit the still developing Earth and created the Moon. This impact also caused the Earths angled spin. The Moon got trapped in Earth's orbit and has stayed ever since. Small astroids have hit the Moon causing craters. The Earth doesn't get hit as much because of our thicker atmosphere. Hope this helps!
If your talking about the chemical equations like combustion, single displacement, etc. Then the equation would be double displacement: AB + CD ---> AD + CB
