Balancing Equations

2Li (s) + 2H2O (l)  2LiOH (aq) + H2 (g) WARM UP 10/17/17 Below is a standard chemical equation. In your IAN Notebook, WRITE this equation and CIRCLE the different parts that you see. Describe what each part you circled is, IF you know what it is. If you DON’T know what a part is, explain what YOU THINK it could be in this equation. Look at this rusty bike wheel. It has been left outside in damp weather too many times, so the iron in the metal parts has rusted. Iron rusts when it combines with oxygen in the air. Iron rusting is an example of a chemical reaction. In a chemical reaction, substances change into entirely different substances. For example, the iron in the bike and the oxygen in the air have changed into rust. 2Li (s) + 2H2O (l)  2LiOH (aq) + H2 (g)

Q: How could you represent the chemical reaction occurring that causes a rusting bicycle, besides just describing it in words? A: Scientists use a standard method to represent a chemical reaction, called a chemical equation. Look at this rusty bike wheel. It has been left outside in damp weather too many times, so the iron in the metal parts has rusted. Iron rusts when it combines with oxygen in the air. Iron rusting is an example of a chemical reaction. In a chemical reaction, substances change into entirely different substances. For example, the iron in the bike and the oxygen in the air have changed into rust. Fe + O2  Fe2O3 (Rust)

Chemical equations are used to represent CHEMICAL REACTIONS Reactants: Zn + I2 Product: Zn I2

Q: What is the general equation for the reaction in which iron rusts? Iron + Oxygen → Iron Oxide (RUST) Or, using symbols: Fe + O2 → Fe2O3 (rust)

Q: What are the reactants and products? Fe + O2 → Fe2O3 (new product - rust) Reactants Products The atoms/compounds you have AFTER the reaction occurs. The atoms/compounds you have BEFORE the reaction occurs.

When is an equation called balanced? When an equation has the same number of atoms of the same kind on both sides.

Chemical Equations 4 Al (s) + 3 O2 (g) ---> 2 Al2O3 (s) The numbers in the front are called coefficients subscripts The letters (s), (g), and (l) are the physical states of the elements/compounds. (aq) – aqueous solution The arrow  means: to yield = to produce = to form

Learning Check What does the “2“ mean in front of LiOH? 2Li (s) + 2H2O (l)  2LiOH (aq) + H2 (g) Number of molecules What does “2“ to the right of “H2” mean? Number of atoms of H What does “(aq)“ to the right of LiOH mean? Aqueous solution What does ““ mean? Yield, form, produce

Q: What is the chemical equation for this reaction? A: The chemical equation is: C + O 2 → CO 2

Q: How have the atoms of the reactants been rearranged in the products of the reaction? C + O 2 → CO 2 A: Carbon atom chemically bonds with two oxygen atoms. HOW ? What bonds are broken and what new bonds have formed?

C + O 2 → CO 2 C + O=O → O=C=O Bonds Break New Bonds Form A: Bonds between the oxygen atoms in the oxygen molecule have been broken, and new bonds have formed between the carbon atom and the two oxygen atoms.

Is this a balanced equation? The charcoal used in a grill is basically carbon. The carbon reacts with oxygen to yield carbon dioxide. The chemical equation for this reaction, C + O2  CO2, R P Count the number of atoms of each element found in the reaction. 1 C 1 C 2 O 2 O Is this a balanced equation? YES

Learning Check Q: What needs to happen for a chemical reaction (change) to take place? A: Bonds between atoms of the reactants break and NEW bonds form, producing new substance.

Q: Is this chemical reaction correct? Explain why. Learning Check Q: Is this chemical reaction correct? Explain why. +  A: No. There are no “pink atoms” on the reactant side – NEW matter (pink) on the product side. Matter canNOT be created.

Q: Is this chemical reaction correct? Explain why. Learning Check Q: Is this chemical reaction correct? Explain why. +  NEW PRODUCTS Why is this reaction correct? B/C atoms must REARRANGE for a chemical reaction to take place

REMEMBER: To balance a chemical equation, you must add COEFFICIENTS (big numbers) in front of the chemical formulas in the equation. You cannot add or change subscripts!!! Why? Because otherwise it will alter the identity of the substance. Ex. O2 – oxygen, if a subscript changed to 3, O3 = ozone The order of the Coefficients in the Chemical Equation is important because this is how you write the COEFFICIENT RATIO.

Balancing using shapes ____H2 + ____O2  ____H2O 2 1 2 Is this reaction balanced? Now fix the H on the left. Double Hydrogen too. Coefficient ratio: 2:1:2 BALANCED !

Balancing Equations using T-chart ___ H2(g) + ___ O2(g) ---> ___ H2O(l) R P Count the number of atoms of each element found in the reaction. H - 2 H - 2 O - 2 O - 1 What Happened to the Other Oxygen Atom????? This equation is NOT balanced!

Balancing Equations using T-chart 2 1 ___ H2(g) + ___ O2(g) ---> ___ H2O(l) 2 R P H - 2 H - 2 O - 2 O - 1 2. Add coefficients to balance the atoms 4 4 2 3. Don’t forget to recount. Now it is balanced! Now fix the H on the left. Don’t forget there is a 1 in front of O2.

Now You Try! Use shapes or T-chart method Fe + O2  Fe2O3 2x2 = 4 _____Fe + ____O2  ____Fe2O3 2 3 2 3x2 = 6 Common multiple Coefficient ratio: 4:3:2

RULE: Balance H and O last Easy Balancing RULE: Balance H and O last Al + O2  Al2O3 2 3 2 1 R P 4 2 1 Al 2 Al 2 x 2 = 4 2 x 3 = 6 2 O 3 O 3 x 2 = 6 2:3 – find a common multiple Coefficient ratio: 4:3:2