CHAPTER 11 Chemical Reactions

Parts of an Equation Iron + Oxygen → Iron (III) Oxide Chemical reactions are written with two parts: REACTANTS: Things you start with. They are at the beginning of the arrow and usually written first (though they don't have to be). PRODUCTS: The things you make. The arrow points to these. These are the things you end with.

Parts of an Equation THE ARROW ALWAYS POINTS TO THE PRODUCTS NO MATTER WHAT! Sometimes, words or symbols will be written on top of the arrow. That's fine. It's called a CATALYST. A catalyst is anything that makes chemical reactions happen faster – like sunlight with plants.

Take 2-3 minutes to label the reactions on your note sheet. - Highlight the reactants blue or green - Circle the products - If there is a catalyst, label it.

Parts of an Equation Its a good idea to indicate which PHASE OF MATTER each substance is in your written chemical reaction. Use these. • (s) – for solids • (l) – for liquids • (g) – if its a gas • (aq) – This one is new for you guys. This means AQUEOUS. Aqueous is when you dissolve a solid into a liquid. Ex: Salt water.

Take 2 minutes to label the phases of matter for the two equations above. Ask a friend if you don't know what phase something is.

Parts of an Equation Sometimes you're going to need to put some numbers in front of the substances in your chemical equation. These numbers are called COEFFICIENTS. Its just like algebra class. Use Coefficients to balance equations. O2 = One oxygen molecule, 2 oxygen atoms. 6 O2 = Six oxygen molecules, 12 oxygen atoms.

On your note sheet, you have a reaction that looks like this: __H2 + __O2 → __H2O Put COEFFICIENT(s) in the blanks to make both sides have the same # of Hydrogens and Oxygens.

Conservation of Mass There is a reason why both sides of the equation have to have the same number of atoms. Law of Conservation of Mass - “Atoms are neither created nor destroyed during a chemical reaction. The combined total mass of the reactants shall be equal to the combined total mass of the products.” That's something you learned about last semester. Basic chemistry. Even John Dalton knew about conservation of mass.

Curve Ball: Diatomic Elements Some elements are written as a pair in chemical equations. You have to memorize which ones they are... • Hydrogen • Chlorine • Nitrogen • Bromine • Oxygen • Iodine • Fluorine Some people say they remember these with the name “Br. HONClIF” but I dunno...

Six steps for writing equations: #1 Write down all the chemical formulas for the Reactant(s) AND the Products(s). It's a good idea to label each substance with the phase of matter that it is in.

Six steps for writing equations: #2 Put the formulas down in order, then draw an arrow that points from R → P like that. Leave room in case you have to add some coefficients later. If there are two or more things on one side of the arrow, put some plus signs between them.

Six steps for writing equations: #3 Count how many of each type of atom are on each side of the equation. If there is a polyatomic ion that appears on both sides, it is usually easier to count that as its own thing instead of each individual element.

Six steps for writing equations: #4 Put coefficients in front of your formulas to balance the equation. WARNING: Don't you dare try to change the formulas of your substances. That's not something you can do, so don't even think about it.

Six steps for writing equations: #5 Double check to make sure you balanced correctly. You need to have the SAME # OF EACH TYPE OF ELEMENT ON BOTH SIDES. People always mess this up, so make sure you double check.

Six steps for writing equations: #6 Simplify all your coefficients if possible. For example in math class you wouldn't write 24/48 , you would just write ½ instead. You won't get full credit on the quiz if you don't simplify your numbers.