1. Get out : Balancing Work Balancing Equation Notes Finish working on Balancing DUE FRIDAY

2. Balancing Chemical Equations Recall the law of conservation of mass: matter is neither created nor destroyed in a chemical reaction. Recall the law of conservation of mass: matter is neither created nor destroyed in a chemical reaction. There is also a conservation of atoms. Atoms do not change in a chemical reaction, they just rearrange. There is also a conservation of atoms. Atoms do not change in a chemical reaction, they just rearrange. THE NUMBER OF ATOMS ON THE REACTANT SIDE MUST EQUAL THE NUMBER OF ATOMS ON THE PRODUCT SIDE. THE NUMBER OF ATOMS ON THE REACTANT SIDE MUST EQUAL THE NUMBER OF ATOMS ON THE PRODUCT SIDE.

3. H 2 CO 3 (aq) H 2 O (l) + CO 2 (g) H = 2 H = 2 C = 1 C = 1 O = 3 O = 3

4. Coefficient A number placed in front of the reactant or product to indicate the number of units taking part in the reaction. A number placed in front of the reactant or product to indicate the number of units taking part in the reaction. 2NaOH(aq) + CO 2 (g) Na 2 CO 3 (s) + H 2 O(l) SUBSCRIPTS CANNOT BE CHANGED! SUBSCRIPTS CANNOT BE CHANGED!

5. Balancing Chemical Equations Steps to Balancing an Equation 1. Determine the correct formulas for all the reactants and products in the reaction. Remember the diatomic elements will always have a subscript of 2 when not combined with anything else. (Ex. O2 never O; or N2 never N) 2. In ink, write the formulas for the reactants on the left and the formulas for the products on the right with the arrow in between. If two or more reactants or products are involved, separate their formulas with plus signs.

6. Balancing Chemical Equations 3. Count the number of atoms of each element in the reactants and products. 3. Count the number of atoms of each element in the reactants and products. A polyatomic ion appearing unchanged on both sides of the equation can be counted as a single unit. A polyatomic ion appearing unchanged on both sides of the equation can be counted as a single unit.

7. Balancing Chemical Equations 4. In pencil, balance the elements one at a time by using coefficients. It is best to start with an element other than hydrogen or oxygen. These two elements often occur more than twice in an equation. If some other element occurs more than twice in the equation it is best not to start with it either. In general, you usually start with the metal, then nonmetal, then hydrogen and then oxygen. You MUST NOT attempt to balance an equation by changing the subscripts in the chemical formulas.

8. Balancing Chemical Equations 5. Check each atom or polyatomic ion to be sure that the equation is balanced 6. Finally, make sure that all coefficients are in the lowest possible ratio.

9. 1. Write a word & chemical equation. Magnesium metal and water combine to form solid magnesium hydroxide and hydrogen gas. Word Equation Word Equation magnesium + water → magnesium hydroxide + hydrogen

10. Sample Problem Mg(s) + H 2 O(l) → Mg(OH) 2 + H 2 (g) Mg(s) + H 2 O(l) → Mg(OH) 2 + H 2 (g) Is the magnesium hydroxide ionic or covalent? Is the formula correct? Why is hydrogen H 2 ? Is the chemical equation balanced? NO

11. Mg(s) + H 2 O(l) → Mg(OH) 2 + H 2 (g) Mg(s) + H 2 O(l) → Mg(OH) 2 + H 2 (g) Mg 1 Mg 1 H 2 H 4 O 1 O 2 Mg(s) + 2H 2 O(l) → Mg(OH) 2 + H 2 (g) Mg 1 Mg 1 H 4 H 4 O 2 O 2

12. Sample Problems Write the balanced equation for the reaction between chlorine and magnesium bromide to produce bromine and magnesium chloride. Number 11 on sheet

13. Sample Problems Write the balanced equation for the reaction between aluminum nitrate and ammonium hydroxide to produce aluminum hydroxide and ammonium nitrate. Number 15