IPC 04 Chemical Reactions Energy in Reactions Chemical Equations Law of Conservation of Mass Balancing Equations Classifying Reactions

Law of Conservation of Mass - Mass is neither created nor destroyed! The total mass of the reactants must equal the total mass of the products. 1CH 4 + 2O 2  1CO 2 + 2H 2 O 16 g + 64 g = 44 g + ? g 80 g = 80 g Ex: I n a chemical reaction, 16 g of methane (CH 4 ) combine with 64 g of oxygen to form carbon dioxide (CO 2 ) and water (H 2 O). What is the mass of the water formed? 80 g – 44 g = 36 g H 2 O This is why we balance eqtns. Same # of atoms = same mass! This is why we balance eqtns. Same # of atoms = same mass!

Practice: 1.In a chemical reaction, 4 g of hydrogen combine with 32 g of oxygen to form water What is the mass of the product formed? 2H 2 + O 2  2H 2 O 2. If 60 g of ethane burns in 224 g of oxygen to produce 108 g of water, what is the mass of the remaining product? C 2 H 6 + O 2  CO 2 + H 2 O 4 g + 32 g = ? g 60 g g = ? g g 176 g 36 g Good Job

Chemical Reaction (1) reactants - substances that react. (2) products – NEW substances that form.  Chemical changes milk + vinegar  cheese ReactantsProducts

Energy in Reactions Exothermic means there is a release of heat energy. Endothermic means there is an absorption of heat energy. HOT! COLD!

Exothermic Reaction Heat Energy Released: energy of products is below the energy of reactants.

Endothermic Reaction Heat Energy Absorbed: energy of products is above the energy of reactants.

Hot Packs vs. Cold Packs Hot/cold packs are used by athletes to minimize swelling of injuries such as muscle and joint sprains. They are constructed of a pouch containing a dry chemical plus an inner pouch of water. The hot/cold pack is activated by breaking the seal on the pouch of water and shaking the pack vigorously. This action mixes the water with the chemical starting the exothermic or endothermic reaction. Hot Packs are exothermic (heat released). Cold Packs are endothermic (heat absorbed). SEE Learning VIDEO “Heat Pack”. “Supercooled” Heat Packs: “Crystallization” Click Here

A chemical reaction that produces light. –Ex. Glow sticks are made of plastic with compounds inside. When the glow stick is bent, it breaks the vial. The compounds mix and the stick produces light.

Review: Changes of Matter Chemical Changes: A change that does produce a new substance. Ex: Iron rusts forming iron oxide. Physical Changes: A change that does not produce a new substance. Ex: Ice melts into water.

Physical or Chemical Change? Silver tarnishes Sugar dissolves in water. Chopped wood Leaf changes colors. Butter melts. Chemical Physical

Reaction Symbols Yields or Produces  Solid or precipitate (s) or  Liquid(l) Gas (g) or  Aqueous (acids & bases dissolved in water) (aq) Catalyst (speeds up)   Ni  Heat Added    Reversible Reaction ⇄ Element or compd is added

Identifying a Chemical Equation: 1.Which are the reactants? 2.Which are the products? 3.Which are the coefficients? 4.Which is the subscript? 5.Which is diatomic? 2 Mg + O 2  2 MgO ReactantsProducts Coeff. Sub. Mg + O 2 MgO 2 & 2 (# in front) 2 (# on bottom) O 2 (HOFBrINCl)

Balancing Chemical Equations Mg (s) + O 2 (g)  MgO (s) 1 st Count the number of atoms on both sides of the arrow. Make a list. 2 nd Place a coefficient in front of the elements/compounds so that the total # of atoms in the reactants equals the total # of atoms in the products. Keep polyatomics together and leave diatomics for last. 3 rd Check your work…Count the atoms again. 1 Mg 2 O 1 O

Ex. 1: Mg + HCl  MgCl 2 + H 2 Ex. 2: KClO 3 −   KCl + O 2 1 Mg 1 H2 H 2 1 K 1 Cl 3 O 2 1 Cl 2 2 Cl K 1 Cl 2 2 O

Ex. 3: H 2 + N 2 − Pt  NH 3 Ex. 4: Al + CuSO 4  Al 2 (SO 4 ) 3 + Cu 2 H2 N 1 N 3 H Al1 Cu 1 SO 4 2 Al 3 SO 4 1 Cu Keep Polyatomics together! Ex: sulfate, SO 4

1. H 2 + N 2  NH 3 2. Na + H 2 O  NaOH + H 2 3. H 2 O 2  H 2 O + O 2 4. Al(NO 3 ) 3 + Cu  Cu(NO 3 ) 2 + Al 5. C 4 H 10 + O 2  CO 2 + H 2 O Practice = 13 ODD! = 26 even! 13

Combustion Reactions: Balance “CHO” Ex. 5 C 3 H 8 + O 2  CO 2 + H 2 O Ex. 6. C 5 H 10 + O 2  CO 2 + H 2 O If odd number of O’s, then Double all! Put a 2 in front of “CH” and do it again. If odd number of O’s, then Double all! Put a 2 in front of “CH” and do it again Balance: C first H second O last Balance: C first H second O last = 10 O-atoms = 15 O-atoms = 30 O-atoms

Complete combustion  carbon dioxide Incomplete combustion  carbon monoxide (poisonous & fatal to breathe)  Avoid carbon monoxide poisoning by keeping air filters, the furnace, and heater burners clean.  Do not stay in a closed garage while the car is running. CO 2 CO

Chemical Reactions that impact the environment! What kind of reaction is this? Acid Rain… Disfigures marble & stone. Effects plant life. Effects water life.

Ozone Depletion The ozone protects the Earth from harmful ultra-violet rays. These rays include deadly radiation that can cause skin cancer in humans, and disrupt the reproduction of some animals, and destroy plant life.