keefe 1415 chapter 11 part 1: balancing equations
TRANSCRIPT
Keefe 1415
CHAPTER 11 PART 1: BALANCING EQUATIONS
• The process by which one or more substances are rearranged to form different substances.
WHAT ARE CHEMICAL REACTIONS?
• Reactants Products
Sample: 2Mg (s) + O2(g) 2MgO(s)• Coefficients: Numerals used in an equation to
indicate relative amounts of reactants and products.
COMPONENTS FOR CHEMICAL EQUATIONS
Like INGREDIENTS for a reaction
END RESULT or GOAL for a reaction
WAYS TO DENOTE CONDITIONS FOR REACTIONS.
• When on their own, they exist as a pair of atoms to form a molecule.
• Br2 bromine gas or liquid, I2 iodine gas or crystal , N2
nitrogen gas, Cl2 chlorine gas, H2 hydrogen gas, O2
oxygen gas, F2 fluorine gas
“BrINClHOF”
DIATOMIC MOLECULES“THE MAGNIFICENT SEVEN”
• Word problem: Hydrogen gas and oxygen gas react to yield water vapor
Word equation: Hydrogen (g) + Oxygen(g) Water (l)
• Skeleton equation:
H2(g) + O2(g) H2O(l)
REPRESENTING CHEMICAL EQUATIONS.
BALANCE THE REACTION:
2H2(g) + O2(g) 2 H2O(l)
BALANCING EQUATIONS
• Key Law:
“Conservation of Matter”!• Must have the same number (#) of
atoms (mass) on the reactant side as on the product side!!!
BALANCING EQUATIONS
• Which windows represent (1) the reactants and (2) the products for the following reaction?
• 2NO(g) + O2(g) → 2NO2(g)
QUESTION USING THE LAW OF CONSERVATION OF MATTER.
• Determine the correct formulas and physical states of reactants & products.
• Write a skeleton equation with reactants & products.
• Count atoms for each element in the reactants & products.
• Balance two sides of chemical reaction with whole number coefficients. (NEVER change subscripts for ANY reason!!!)
• Check each element or polyatomic ion is balanced on both sides. Make sure the coefficients are the SIMPLEST whole number ratio!!!
GENERAL SUMMARY STEPS TO BALANCING EQUATIONS.
BALANCING USING A GRID
Al(s) + HCl(aq) H2(g) + AlCl3(s)
Draw the chart:
Elements Reactants Products
Al
H
Cl
USING A GRID WITH POLYATOMICS
Pb(NO3)4 (aq) + CuSO4 (aq) Pb(SO4)2(s) +Cu(NO3)2(aq)
Components Reactant Product
Pb
NO31-
Cu
SO42-
• Yes, but we use the common denominator to convert them to whole numbers.
• Remember, the coefficients are ratios, just like the subscripts for each compound.
CAN COEFFICIENTS BE REPRESENTED AS FRACTIONS?
EXAMPLE OF A COEFFICIENT AS A FRACTION.
C2H6(g) + O2(g) CO2(g) + H2O(l)
Elements Reactant Product
C
H
O
BALANCE THE FOLLOWING REACTIONS:
BALANCE THE FOLLOWING REACTIONS:
WHAT WE MAY LOOK FOR IN A CHEMICAL REACTION!!
• Temperature change (energy change)
• Precipitate forming (solid from two aqueous solutions)
• Formation of a gas
• Smoke (for when it buuuuuurns)
• Color change
• Odor (not best, but possible indicator)
• pH change
TYPES OF REACTIONS1. Synthesis reactions
2. Decomposition reactions
3. Single displacement reactions
4. Double displacement reactions
5. Combustion reactions
6. Neutralization reactions
You need to be able to identify each type.
1. SYNTHESIS
Example C + O2
OO C + O O C
General: A + B AB
EX. SYNTHESIS REACTION
PRACTICE
• Predict the products and balance the reactions.
Na(s) + Cl2(g)
Mg(s) + F2(g)
Al(s) + F2(g) •.
MORE PRACTICE: GIVE THE FORMULAE, PREDICT PRODUCTS, AND BALANCE
• Sulfur dioxide gas is bubbled through water• Solid potassium oxide is added to a
container of carbon dioxide gas• A piece of sodium is added to a container
of iodine vapor
2. DECOMPOSITION
Example: NaCl
General: AB A + B
Cl Na Cl + Na
EX. DECOMPOSITION REACTION
DECOMPOSITION PRACTICE:
• balance:
• H2O ---> H2 + O2
GIVE THE FORMULA, PREDICT THE PRODUCTS, AND BALANCE:
3. SINGLE DISPLACEMENT (AKA SINGLE REPLACEMENT)
Example: Zn + CuCl2
ZnClCl Cu +
General: AB + C AC + B
ClCl Zn Cu+
Zn was oxidized
Went from neutral (0) to (+2)
Cu was reduced
Went from (+2) to Neutral (0)
EX. SINGLE REPLACEMENT REACTION
SINGLE REPLACEMENT REACTIONS• Predict the product and balance the following
single replacement reaction equations:
• Zn(s) + HCl(aq)
• NaCl(s) + F2(g)
• Al(s)+ Cu(NO3)2(aq)
MORE PRACTICE:
4. DOUBLE REPLACEMENT
Example: MgO + CaS
General: AB + CD AD + CB
SOMg Ca
+O S
Mg Ca+
DOUBLE REPLACEMENT REACTIONS
• Think about it like “foil”ing in algebra, first and last ions go together + inside ions go together
• Example:
AgNO3(aq) + NaCl(s) AgCl(s) + NaNO3(aq)
• Another example:
K2SO4(aq) + Ba(NO3)2(aq) KNO3(aq) + BaSO4(s)
PRACTICE• Predict the products. Balance as necessary.
1. HCl(aq) + AgNO3(aq)
2. CaCl2(aq) + Na3PO4(aq)
3. Pb(NO3)2(aq) + BaCl2(aq)
4. FeCl3(aq) + NaOH(aq)
5. KOH(aq) + CuSO4(aq)
COMBUSTION REACTIONS• In general:
CxHy + O2 CO2 + H2O
• Products are ALWAYS
carbon dioxide and water.
COMBUSTION
• Example• C5H12 + O2 CO2 + H2O
• Write the products and balance the following combustion reaction:• C10H22 + O2
MORE PRACTICE:
NEUTRALIZATION
• Acid + base a salt + water• ***acid formulae always start with H• *** bases always end in hydroxide and
START with alkali or alkaline earth metals
• Example: HBr + NaOH ---> NaBr + H2O
PREDICT THE PRODUCT AND BALANCE:
MIXED PRACTICE• State the type, predict the products, & balance.
1. BaCl2 + H2SO4
2. C6H12 + O2
3. Zn + CuSO4
4. Cs + Br2
5. FeCO3
6. NH4OH + HBr