Properties of Matter You have already looked at

Properties of Matter You have already looked at the difference between physical changes and chemical changes. Remember: A chemical change occurs when a substance changes into a new substance with different chemical properties e. g. iron rusting or burning charcoal.

Equations Chemical reactions involve many chemicals, as in explosions of dynamite, bathroom cleaners working on a stain or as in the growth of your body. Chemists use a word equation to represent these types of reactions…it tells us what reacts and what is produced.

The starting materials in a chemical change are called reactants and the new materials made are called products. Iron + oxygen Fe + makes O 2 Reactants rust or iron (III) oxide makes Fe 2 O 3 Products

Equation format: All the reactants All the products Reactants and products can be separated by a (+) sign Reactant 1 + Reactant 2 Product 1 + Product 2 Example: hydrogen + oxygen water

Conserving Mass The Law of Conservation of Mass states that in a chemical reaction, the total mass of the reactants is always equal to the total mass of the products. This is because during the chemical reaction the individual atoms that make up the reactants are simply rearranged into new patterns or products, no matter is lost or added during the process. hydrogen + oxygen 25 g 10 g water ? g http: //www. youtube. com/watch? v=Wwmsy 4 hu. ZQ 0

Skeleton Equations A skeleton equation is representation of a chemical reaction in which the formulas of the reactants are connected to the formulas of the products by an arrow. e. g. methane + oxygen carbon dioxide + water (word equation) CH 4 + O 2 CO 2 (skeleton equation) + H 20

Worksheet Skeleton Equations. Homework

The problem with a skeleton equation is that it does not follow the Law of Conservation of Mass. By looking at the # of atoms on each side of the above equation we can see that they are not the same on both sides of the equation. CH 4 1 C + O 2 + CO 2 2 O 4 H 16 g 32 g 48 g + H 20 (skeleton equation) 1 C + 2 H 2 O 1 O 44 g 18 g 62 g (mass is not the same)

To make the equation follow the Law of Conservation of Mass we must rewrite it as a balanced equation. To do this we will use multipliers at the front of each chemical formula. These multipliers are called coefficients. These allow us to get the same number of atoms on each side of the equation. CH 4 + 2 O 2 CO 2 1 C + 4 O 1 C + 4 H 2 O 2 O 4 H 16 g 64 g 80 g 44 g = + 2 H 20 36 g 80 g (mass is now the same)

Balancing Equations Activity

Wednesday, March 10, 2010

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Homework Check/Review 2 questions from balancing equations

Balancing Equations Finish balancing equations sheet from yesterday

How to balance an Equation 1) write the word equation for the reaction Lead (II) Nitrate + Potassium Iodide Lead(II) Iodide + Potassium Nitrate 2) Write the skeleton equation by replacing each name with the correct formula Pb(NO 3)2 + KI Pb. I 2 + KNO 3

3) Count the # of atoms of each type in the reactants and products Pb(NO 3)2 Pb: 1 N: 2 K: 1 I: 1 O: 6 + KI Pb. I 2 + KNO 3 Pb: 1 N: 1 K: 1 I: 2 O: 3 *** Use the ECHO rule : Count and balance the atoms in this order Element (all) then Carbon Hydrogen and finally Oxygen

4) multiply each of the formulas by the appropriate coefficients to balance the number of atoms Pb(NO 3)2 + 2 Pb: 1 N: 2 K: 1 2 I: 1 2 O: 6 KI Pb. I 2 + 2 KNO 3 Pb: 1 N: 1 2 K: 1 2 I: 2 O: 3 6 We now have the same number of each element on both sides so the equation is balanced.

Worksheet Balancing Equations

Homework Check Balancing Equations Worksheet

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Worksheet Finish Balancing Equations Sheet (from yesterday)

Worksheet New Balancing Equations Sheet

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Balancing Equations- Review Balance each of the following equations: 1. Al + O 2 Al 2 O 3 2. Na. OH + HBr Na. Br + H 2 O 3. Mg + N 2 Mg 3 N 2 4. Co + Cl 2 Co. Cl 5. Ca + OH Ca(OH)2