Chemical Reactions!!!

Writing Chemical Equations Reactants are the starting substances ◦ Found on the left side of the equation Products are the substances formed ◦ Found on the right side of the equation

Writing Chemical Equations An arrow is used to separate reactants from products A plus sign separates each reactant or each product Reactant 1 + Reactant 2  Product 1 + Product 2

Balancing Chemical Equations The law of conservation of mass indicates that matter is neither created nor destroyed. ◦ We must show mass conservation in our chemical equations.

Balancing Chemical Equations Look at the following equation: Fe + Cl 2  FeCl 3 We have one iron on each side. But on the reactant side we have 2 Cl and there are 3 Cl’s on the product side. We must make the number of atoms of each reactant and each product equal.

Balancing Chemical Equations 2Fe + 3Cl 2  2FeCl 3 + 

Balancing Chemical Equations Steps: ◦ Write the skeleton equation (if not given). ◦ Count the atoms of the elements in the reactants. ◦ Count the atoms of the elements in the products. ◦ Change the coefficients to make the number of atoms of each element equal on both sides of the equation. ◦ Make sure coefficients are in the lowest possible ratio.

Balancing Chemical Equations Tips: ◦ Start with balancing the most complicated compound:  C 2 H 6 + O 2  CO 2 + H 2 O  Start with C 2 H 6 and balance C’s and H’s first.  C 2 H 6 + O 2  2CO 2 + 3H 2 O  How many O’s are on the right now? What coefficient do we need to put in front of O 2 ?  C 2 H O 2  2CO 2 + 3H 2 O ◦ Multiply coefficients to get whole numbers:  2C 2 H 6 + 7O 2  4CO 2 + 6H 2 O

Balancing Chemical Equations Tips: ◦ If a polyatomic ion stays together you can balance the entire ion as a group.  AlCl 3 + Ca 3 (PO 4 ) 2  AlPO 4 + CaCl 2.  Since all the P and O’s are found in PO 4 and the phosphate stays together, you can balance the PO 4 ’s as a group. Where do we start?  2AlCl 3 + Ca 3 (PO 4 ) 2  2AlPO 4 + 3CaCl 2

Balancing Chemical Equations: 2 Methods Balancing by inspection: ◦ The method that we have been using so far. If you can look at and figure out what coefficients to add, then you can balance by inspection. Atom Inventory method: ◦ If you have been having trouble following what coefficients to add, there is another method that is more work but will help you figure out the coefficients.

Balancing Chemical Equations/ Atom Inventory 1 O 2 H 2 O 2 H NOT BALANCED water hydrogen oxygen + H2OH2OH2H2 + O2O2 2

2 O 2 H NOT BALANCED 2 O 4 H water Balancing Chemical Equations/ Atom Inventory hydrogen oxygen + H2OH2OH2H2 + O2O2 22

H 2 O(l) H 2 (g) + O 2 (g) 2O 4 H 2O 4 H BALANCED 22 Always go back and double check! * * water Balancing Chemical Equations/ Atom Inventory Method hydrogen oxygen +

ZnZnCl 2 + H2H2 HCl + 1 Zn 1 Cl 1 H 1 Zn 2 Cl 2 H NOT BALANCED 2 Atom Inventory Sample 2 Zinc + hydrochloric acid  zinc chloride + hydrogen

ZnZnCl 2 + H2H2 HCl + 1 Zn 2 Cl 2 H 1 Zn 2 Cl 2 H 2 BALANCED Always go back and double check! * * * Atom Inventory Sample 2 Zinc + hydrochloric acid  zinc chloride + hydrogen

Atom Inventory Sample 3 Aluminum carbide (Al 4 C 3 ) + water  methane(CH 4 ) + aluminum hydroxide Al 4 C 3 H2OH2O+CH 4 +Al(OH) 3

Atom Inventory Sample 3 Aluminum carbide (Al 4 C 3 ) + water  methane(CH 4 ) + aluminum hydroxide Al 4 C 3 4 Al 3 C 1 OH 1 H 1 Al 1 C 3 OH 4 H HOH+CH 4 +Al(OH) 3 4

Atom Inventory Sample 3 Aluminum carbide (Al 4 C 3 ) + water  methane(CH 4 ) + aluminum hydroxide Al 4 C 3 4 Al 3 C 1 OH 1 H 4 Al 1 C 12 OH 4 H HOH+CH 4 +Al(OH) 3 43

Atom Inventory Sample 3 Aluminum carbide (Al 4 C 3 ) + water  methane(CH 4 ) + aluminum hydroxide Al 4 C 3 4 Al 3 C 1 OH 1 H 4 Al 3 C 12 OH 12 H HOH+CH 4 +Al(OH)

Atom Inventory Sample 3 Aluminum carbide (Al 4 C 3 ) + water  methane(CH 4 ) + aluminum hydroxide Al 4 C 3 4 Al 3 C 12 OH 12 H 4 Al 3 C 12 OH 12 H HOH+CH 4 +Al(OH) * BALANCED * * *

Atom Inventory Sample 4 Aluminum sulfate + calcium hydroxide  aluminum hydroxide + calcium sulfate Al 2 (SO 4 ) 3 Ca(OH) 2 + Al(OH) 3 + CaSO Al 1 Ca 3 SO 4 2 OH 1 Al 1 Ca 1 SO 4 3 OH

Atom Inventory Sample 4 Aluminum sulfate + calcium hydroxide  aluminum hydroxide + calcium sulfate Al 2 (SO 4 ) 3 Ca(OH) 2 + Al(OH) 3 + CaSO Al 1 Ca 3 SO 4 2 OH 2 Al 1 Ca 1 SO 4 6 OH

Atom Inventory Sample 4 Aluminum sulfate + calcium hydroxide  aluminum hydroxide + calcium sulfate Al 2 (SO 4 ) 3 Ca(OH) 2 + Al(OH) 3 + CaSO Al 1 Ca 3 SO 4 2 OH 2 Al 3 Ca 3 SO 4 6 OH 3

Atom Inventory Sample 4 Aluminum sulfate + calcium hydroxide  aluminum hydroxide + calcium sulfate Al 2 (SO 4 ) 3 Ca(OH) 2 + Al(OH) 3 + CaSO Al 3 Ca 3 SO 4 6 OH 2 Al 3 Ca 3 SO 4 6 OH * * * * BALANCED

Practice: carbon tetrachloride + oxygen  carbon dioxide + water carbon disulfide + oxygen  carbon dioxide + sulfur dioxide

Predicting Products If you are only given the reactants for a chemical reaction, you will need to predict the products for that reaction. The products can be determined based on the type of reaction.

Predicting Products Synthesis (S) ◦ Reactants will be two elements. ◦ If the reactants are two elements, what is the only possible product?  Compound formed by those elements.

Predicting Products Synthesis (S) 1.Na + Cl 2  2.Mg + N 2  NaCl Mg 3 N 2

Predicting Products Decomposition (D) ◦ Reactant will be one compound ◦ If the reactant is one compound, what would be the products?  Elements in that compound.

Predicting Products Decomposition (D) 1.CaO  2.HCl  Ca + O 2 H 2 + Cl 2

Predicting Products Single Replacement (SR) ◦ Reactants will be one compound and one element. ◦ A couple and a single guy go to a dance. The guy ends up splitting up the couple and taking the girl from the other guy. The guy in the original couple goes home alone.

Predicting Products Single Replacement (SR) 1.Mg + HCl  2.NaCl + F 2  MgCl 2 + H 2 NaF + Cl 2

Predicting Products Double Replacement (DR) ◦ Reactants will be two compounds. ◦ Two couples go a dance. During the dance the two couples break up and “switch partners”.

Predicting Products Double Replacement (DR) 1.AgNO 3 + HCl  2.Na 2 SO 4 + BaCl 2  AgCl + HNO 3 NaCl + BaSO 4

Predicting Products Combustion(C) ◦ Reactants are a compound with C,H, possibly O, and always O 2. ◦ Products are usually CO 2 and H 2 O

Predicting Products Combustion (C) 1.C 6 H 6 + O 2  2.C 2 H 5 OH + O 2  CO 2 + H 2 O

Molecular/Net Ionic Equations All reactions written so far have been molecular equations, showing everything in the reaction. Not everything in an equation actually takes part in the reaction. SR and DR reactions have “spectator” ions that are present but don’t actually take part. Net Ionic Equation omits the spectators.

Molecular/Net Ionic Equations We will only write Net Ionics for DR reactions. DR rxns produce a precipitate. The net ionic rxns only involves the precipitate. You must use solubility rules to determine the precipitate.

Molecular/Net Ionic Equations AgNO 3 + KCl  Which of the products is the precipitate (the insoluble product)? AgCl Net Ionic: Ag 1+ + Cl 1-  AgCl AgCl + KNO 3

Molecular/Net Ionic Equations Na 2 SO 4 + BaCl 2  Which of the products is the precipitate (the insoluble product)? BaSO 4 Net Ionic: Ba 2+ + SO 4 2-  BaSO 4 NaCl + BaSO 4