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) + O 2 (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
When on their own, they exist as a pair of atoms to form a molecule. Br 2 bromine gas or liquid, I 2 iodine gas or crystal, N 2 nitrogen gas, Cl 2 chlorine gas, H 2 hydrogen gas, O 2 oxygen gas, F 2 fluorine gas“BrINClHOF” DIATOMIC MOLECULES “THE MAGNIFICENT SEVEN”
Hydrogen gas and oxygen gas react to yield water vapor Word problem: Hydrogen gas and oxygen gas react to yield water vapor Word equation: Hydrogen (g) + Oxygen(g) Water ( l ) Skeleton equation: H 2 (g) + O 2 (g) H 2 O (l) REPRESENTING CHEMICAL EQUATIONS.
BALANCE THE REACTION: 2H 2 (g) + O 2 (g) 2 H 2 O (l)
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) + O 2 (g) → 2NO 2 (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) H 2 (g) + AlCl 3 (s) Draw the chart: ElementsReactantsProducts Al H Cl
USING A GRID WITH POLYATOMICS Pb(NO 3 ) 4 (aq) + CuSO 4 (aq) Pb(SO 4 ) 2(s) +Cu(NO 3 ) 2(aq) ComponentsReactantProduct Pb NO 3 1- Cu SO 4 2-
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. C 2 H 6(g) + O 2(g) CO 2(g) + H 2 O ( l ) ElementsReactantProduct C H O
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 REACTIONS 1.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 + O 2 OO C + OO C General: A + B AB
PRACTICE Predict the products and balance the reactions. Na (s) + Cl 2(g) Mg (s) + F 2(g) Al (s) + F 2(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
DECOMPOSITION PRACTICE: balance: H 2 O ---> H 2 + O 2
GIVE THE FORMULA, PREDICT THE PRODUCTS, AND BALANCE:
3. SINGLE DISPLACEMENT (AKA SINGLE REPLACEMENT) Example: Zn + CuCl 2 Zn Cl Cu + General: AB + C AC + B Cl Zn Cu + Zn was oxidized Went from neutral (0) to (+2) Cu was reduced Went from (+2) to Neutral (0)
4. DOUBLE REPLACEMENT Example: MgO + CaS General:AB + CD AD + CB S O Mg 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: AgNO 3(aq) + NaCl (s) AgCl (s) + NaNO 3(aq) Another example: K 2 SO 4(aq) + Ba(NO 3 ) 2(aq) KNO 3(aq) + BaSO 4(s)
PRACTICE Predict the products. Balance as necessary. 1.HCl (aq) + AgNO 3(aq) 2.CaCl 2(aq) + Na 3 PO 4(aq) 3.Pb(NO 3 ) 2(aq) + BaCl 2(aq) 4.FeCl 3(aq) + NaOH (aq) 5.KOH (aq) + CuSO 4(aq)
COMBUSTION REACTIONS In general: C x H y + O 2 CO 2 + H 2 O Products are ALWAYS carbon dioxide and water.
COMBUSTION Example C 5 H 12 + O 2 CO 2 + H 2 O Write the products and balance the following combustion reaction: C 10 H 22 + O 2
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 + H 2 O