Balanced Equation Atoms can’t be created or destroyed All the atoms we with we must up with A balanced equation has the of each element on of the equation.
C + O 2 CO 2 This equation is already balanced What if it isn’t? C + O O C O O
C + O 2 CO Need one more O in the. Can’t change the, because it describes what it is (carbon monoxide in this example) C + O C O O
Must be used to make another But where did the other C come from? C + O C O O O C
Must have started with two C C + O C O O O C C
Finding the number of atoms The subscript in front of an element is the number of atoms of that element / polyatomic. Ex) CO 2 B 2 (SO 4 ) 3 C= O=B=SO 4 = A coefficient in front of the formula multiplies the amount of elements by the coefficient. Ex) 3CO 2 2B 2 (SO 4 ) 3 C= O=B=SO 4 =
Finding the number of atoms H2OH2OH=O= 2H 2 OH=O= B(NO 3 ) 2 B=NO 3 = 3B(NO 3 ) 2 B=NO 3 = Pb 3 (PO 4 ) 4 Pb=PO 4 = 2Pb 3 (PO 4 ) 4 Pb=PO 4 =
Rules for balancing: . Determine the for reactants and products. . Write a equation.
Rules for balancing: 3. Count the of atoms of each appearing on sides of the equation. 4. Balance the elements one at a time by adding (the numbers in front) -Save and until LAST!
Rules for balancing: 5. Check to make sure it is balanced. 6. Make sure the coefficients are in the possible ratio.
Don’t you ever… Never change a to balance an equation. H 2 O is a different compound than H 2 O 2 Never put a coefficient in the of a formula 2 NaCl is okay, Na2Cl is not. X
Section 8.2 Types of Chemical Reactions OBJECTIVES: Identify a reaction as combination, decomposition, single-replacement, double- replacement, or combustion
Types of Reactions 5 major types. predict the products predict whether or not they will happen at all How? We recognize them by their
#1 - Combination Reactions Combine - put together substances combine to make one. A + B Ca +O 2 CaO SO 3 + H 2 O H 2 SO 4
#1 - Combination Reactions We can predict the products if they are two elements. Mg + N 2
Write and balance Ca + Cl 2 Fe + O 2 iron (II) oxide Al + O 2 Remember that the first step is to write the correct formulas Then balance by using only
#2 - Decomposition Reactions Decompose = fall apart reactant falls apart into elements or compounds. AB A + B
#2 - Decomposition Reactions NaCl Na + Cl 2 CaCO 3 CaO + CO 2 Note that is usually required to decompose
#2 - Decomposition Reactions Binary compounds (made of 2 elements) f alls apart into its elements H 2 O HgO
#3 - Single Replacement Reactions element another (new dance partner) Reactants are an Products will be a element and different cmpd Li + KCl K + LiCl F 2 +2 LiCl 2LiF + Cl 2 (Cations switched) (Anions switched)
#3 Single Replacement Reactions Metals replace other metals (and H) K + AlN Zn + HCl Think of water as: HOH Metals replace first H, then combines w/ hydroxide (OH). Na + H 2 O
#3 Single Replacement Reactions Sometimes, the reaction will happen: Some chemicals are more “ ” than others active replaces active
The “Activity Series” of Metals Lithium Potassium Calcium Sodium Magnesium Aluminum Zinc Chromium Iron Nickel Lead Hydrogen Bismuth Copper Mercury Silver Platinum Gold If the lone metal is the paired metal, replacement occur. Ex) Li + NaCl Na + LiCl If the lone metal is the paired metal, replacement will occur. Ex) Na + LiCl Na + LiCl Higher activity Lower activity
The “Activity Series” of Halogens Fluorine Chlorine Bromine Iodine If the lone halogen is the paired halogen, replacement occur. 2NaCl (s) + F 2(g) MgCl 2(s) + Br 2(g) Higher Activity Lower Activity
#3 Single Replacement Reactions Practice: Fe + CuSO 4 Pb + KCl Al + HCl Lithium Potassium Calcium Sodium Magnesium Aluminum Zinc Chromium Iron Nickel Lead Hydrogen Bismuth Copper Mercury Silver Platinum Gold Higher activity Lower activity
#4 - Double Replacement Reactions things each other. Reactants must be two compounds. NaOH + FeCl 3 positive ions change place NaOH + FeCl 3 Fe +3 OH - + Na +1 Cl -1 =
Complete and balance: assume all of the following reactions actually take place: CaCl 2 + NaOH CuCl 2 + K 2 S KOH + Fe(NO 3 ) 3 K 2 SO 4 + BaF 2
How to recognize which type? Look at the reactants: El + El =Combination Cpd =Decomposition El + Cpd =Single replacement Cpd + Cpd =Double replacement
Practice Examples: H 2 + O 2 H 2 O Zn + H 2 SO 4 HgO KBr + Cl 2 AgNO 3 + NaCl Mg(OH) 2 + H 2 SO 3
#5 – Combustion Reactions Combustion means “ ” Normally, a cpd composed of only C, H, (sometimes O) is reacted with oxygen – called “burning” combustion, products are
Combustion Reaction Examples: C 4 H 12 + O 2 C 6 H 12 O 6 + O 2 C 8 H 8 + O 2
SUMMARY: An equation... Describes a rxn Must be only balance by changing special symbols to indicate physical state, catalyst or energy required, etc.
Reactions 5 major types We can tell what type they are by looking at Single Replacement happens based on the Series
Section 11.3 p. 342 Reactions in Aqueous Solution Co(NO 3 ) 2 K 2 Cr 2 O 7 K 2 CrO 4 NiCl 2 CuSO 4 KMnO 4
Net Ionic Equations Many reactions occur in water, or solution When dissolved in water, many ionic cpds “dissociate”, or, into cations & anions Now write ionic equation
Net Ionic Equations Example (needs to be a double replacement reaction) AgNO 3 + NaCl AgCl + NaNO 3 1. this is the full balanced equation 2. next, write it as ionic equation by splitting the cpds into their ions: Ag 1+ + NO 3 1- + Na 1+ + Cl 1- AgCl(s) + Na 1+ + NO 3 1- Solids do not split up.
Net Ionic Equations 3. Crossing out ions that did not change (called spectator ions) Ag 1+ + Cl 1- AgCl (s) This is the
Predicting the Precipitate Insoluble salt is a precipitate i.e. a solid General solubility rules are found: a)Table 11.3, p. 344 in textbook