1. 7.4 Balancing Chemicals Equations By: Brenda Tran and Ziba Sultani

2. What is a balanced equation? • Each side of the equation has the same number of atoms of each element Example:

3. Symbols used in Equations Reactant – the starting substance of a chemical reaction, usually on the left side of the equation Product – the substance that is formed after the chemical reaction occurs; on the right side of the equation

4. Balancing the equation is necessary to be consistent with the law of ______________. a. Conservation of momentum b. Conservation of energy c. Conservation of mass d. All of the Above Fun Fact!

5. Rules of Balancing Equations • Write the right formula with the reactants and products. • Now, write the equation with the reactants, yields, and products. If there are more than 2 reactants, use plus signs to separate it. • Count how many atoms are on each side of the equation. A polyatomic ion shows uncharged on both sides, counted as single units. • One at a time, balance the elements using coefficients. When there’s no coefficient, it’s assumed that it’s a 1. Don’t try to balance the equation by changing the subscripts in the formula. • Check each atom or polyatomic ion and see if the equation is balanced. • Keep in mind that the coefficients are in the lowest possible ratio.

6. Unbalanced!

7. How to make it balanced • Whenever hydrogen and oxygen react with each other, they make water! H₂(g) + O₂(g) → H₂O(l) H₂(g) + O₂(g) → 2H₂O(l)

8. Another interaction SnO₂+ H₂ → Sn + H₂O SnO₂ + 2H₂ → Sn + 2H₂O

9. Al(s) + O₂(g) → Al₂O₃ (s) 4Al(s) + 3O₂(g) → 2Al₂O₃(s)

10. FACT: • If the mass of a product does not equal the mass of reactants, then it does not follow the law of conservation of mass. Why is it important?

11. Homework and help • ___ Fe + ___ O₂ → ___ Fe₂O₃ • ___ Na + ___ H₂O → ___ NaOH + ___ H₂ • ___ Zn + ___ HCl → ___ ZnCl₂ + ___ H₂ http://web.jjay.cuny.edu/~acarpi/NSC/6-react.htm http://www.webqc.org/balance.php http://www.sky-web.net/science/balancing_chemical_equations.htm