By Aimee Chavez

Chemical Equations Tells the substances present before and after the reaction. Reactants: what you start with Products: what you end with

Conservation of Mass In a chemical reaction the mass of the products always equals the mass of the reactants. The law of conservation of mass states that mass is neither created nor destroyed in a chemical reaction.

Balancing Equations In order to show that mass is conserved during a reaction, a chemical equation must be balanced. Coefficients are numbers that appear before the formulas can be changed to balance an equation. Subscripts appear below and after an element or compound.

Tips If a molecule or compound has a coefficient and a subscript you multiply them together to find the total number of elements. For example 2H₂O = H:4 and O:2

Step One 1. Count the number of atoms of each element on each side of the equation. Be careful to count correctly with coefficient in front of a compound or molecules. For example the 2 in front of 2NaOH means Na:2 O : 2 and H : 2

Step Two 2. Change one or more coefficients until the equation is balanced. You always use the lowest possible coefficient. Start on the right or left and keep going until it is balanced.

Examples 1. _____ H2 + _____ O2 _____ H2O 2. _____ N2 +_____ H2 _____ NH3 3. _____ S8 + _____ O2 _____ SO3 4. _____ N2 + _____ O2 _____ N2O

Classifying Reactions Types:

Type of Reaction Definition  Equation Synthesis Decomposition Single Replacement Double Replacement A = Red B = Blue C = Green D = Yellow A + B → AB AB → A + B AB + C → AC + B AB + CD → AC + BD Two or more elements or compounds combine to make a more complex substance Compounds break down into simpler substances Occurs when one element replaces another one in a compound Occurs when different atoms in two different compounds trade places

Identifying Chemical Reactions ____ P + O 2 → P 4 O 10 ____ Mg + O 2 → MgO ____ HgO → Hg + O 2 ____ Al 2 O 3 → Al + O 2 ____ Cl 2 + NaBr → NaCl + Br 2 ____ H 2 + N 2 → NH 3 2. Use colored pencils to circle the common atoms or compounds in each equation to help you determine the type of reaction it illustrates. Use the code below to classify each reaction. S = Synthesis D = Decomposition SR = Single Replacement DR = Double Replacement

____ Na + Br 2 → NaBr ____ CuCl 2 + H 2 S → CuS + HCl ____ HgO + Cl 2 → HgCl + O 2 ____ C + H 2 → CH 4 ____ KClO 3 → KCl + O 2 ____ S 8 + F 2 → SF 6 ____ BaCl 2 + Na 2 SO 4 → NaCl + BaSO 4

Speeding up Chemical Reactions 1. Breaking a solid into smaller sizes (to increase its surface area) 2. Increase the concentration ( ↑ substance) 3. Increase the temperature ( more kinetic energy) 4. Decreasing volume 5. Adding a catalyst

Catalysts A substance that modifies and increases the rate of a reaction without being consumed in the process.

Enzymes Image result for enzymeswww.chem4kids.com Enzymes are biological molecules (proteins) that act as catalysts and help complex reactions occur everywhere in life. Let's say you ate a piece of meat. Proteases would go to work and help break down the peptide bonds between the amino acids.

Inhibitors a substance that decreases the rate of or stops completely a chemical reaction. Some reactions put out lots of heat. Extra heat may cause safety hazards - the engine may catch fire - or increase the likelihood of unwanted side reactions. (Watch out for that tree…) Inhibitors also prevent chemical damage or decay in finished products. An anti-rust coating on your car is a good example of this. Used in food production.

Chemical Changes 1.Odor or Change in taste: (sour), Curdling of milk, browning fruit 2. Change in Color : Rusting/tarnishing, hair dye or bleach, toast, burning toast or food 3. Production of gas:(expanding /rising & bubbles), Baking a cake or bread, Making cheese 4. Hissing or Loud Noise (fire works) 5. Formation of precipitate 6. Protein rearrangement: frying and egg, eggs in baking a cake 7.Change in temperature: violent reaction (Fireworks) that has heat as a product ( endothermic / exothermic)

Endothermic vs. Exothermic