Convert the following word equations into formula equations by changing element and compound names into chemical formulas.
1. sodium + oxygen → sodium oxide
2. copper + silver nitrate → copper(II) nitrate + silver
3. aluminum chlorate + barium sulfate → aluminum sulfate + barium chlorate
4. bromine + calcium iodide → calcium bromide + iodine
5. zinc sulfide + magnesium arsenate → zinc arsenate + magnesium sulfide
6. cobalt + lead(II) nitrite → cobalt(III) nitrite + lead
7. potassium + water → potassium hydroxide + hydrogen