Balancing Chemical Equations and Types of Chemical Reactions Boon Chemistry

Objectives I can compare and contrast different types of chemical reactions. I can define and identify a balanced chemical equation. I can balance simple chemical equations.

Parts of a Chemical Reaction Reactants Products Cu (s) + 2 AgNO3 (aq) → Cu(NO3)2 (aq) + 2 Ag (s) Letters in parentheses show the state of matter. Coefficients (numbers) in front of a chemical formula show “how many.” Reaction: http://www.youtube.com/watch?v=Sn1dkafX9As&feature=fvwrel http://www.youtube.com/watch?v=rgYhkVy5cBU The arrow separates the reactants and products.

Balancing a Chemical Reaction Equation Atoms are not created or destroyed during a chemical reaction. Scientist know that there must be the same number of atoms on each side of the arrow.

__Cu + __ AgNO3 → __Cu(NO3)2 + __ Ag Is it balanced? __Cu + __ AgNO3 → __Cu(NO3)2 + __ Ag Cu = Cu = Ag = Ag = NO3 = NO3 =

Balancing a Chemical Reaction Equation To balance the chemical equation, you must add coefficients to the different parts of the equation. Cu (s) + 2 AgNO3 (aq) → Cu(NO3)2 (aq) + 2 Ag (s)

Steps for Balancing Chemical Reaction Equations Determine number of atoms for each element for the reactants and products separately. Try to add coefficients to the equation to get the same number of atoms on each side. Note: Coefficients multiply the atoms in the compound. Keep the compound formulas the same. Do not change subscripts. Hint: Balance anything that is not hydrogen or oxygen first. Then balance hydrogen. Balance oxygen last.

Why do we balance Chemical Reactions? http://www.youtube.com/watch?v=ODf_sPexS2Q http://www.youtube.com/watch?NR=1&v=92Mfric7JUc&feature=endscreen http://www.youtube.com/watch?v=IgU4nwdBrIA&feature=related Focus Questions: How are the two reactions the same? How are they different? Why? If you wanted to do these reactions at home, what would you need to know?

Law of Conservation of Mass Matter cannot be created or destroyed in a chemical reaction The number of atoms on the reactant side must equal the atoms of the products + H2  H2O O2 (g) (l) O H O H H H O Unbalanced! Balanced!

Balanced Chemical Equations A chemical equation is “balanced” when there are the same number of atoms of each element on both sides of the arrow. NaHCO3 (s) + HC2H3O2 (aq) èNaC2H3O2 (aq) + CO2 (g) + H2O (l) Is it balanced? Reactants Products Na = 1 H = 5 C = 3 O = 5

Is it balanced? Practice Determine the number of atoms of each element in the reactants and products. Then, state whether the equation is balanced. P4 + O2 → P2O5 C3H8 + O2 → CO2 + H2O Ca2Si + Cl2 → CaCl2 + SiCl4 Si + CO2 → SiC + SiO2 Not balanced. Not balanced. Not balanced. Not balanced.

+ 2 2 H2 H2O O2 Balancing Equations  (g) (l) H = O = 2 4 H = O = 2 4 coefficient 2 2 H2  H2O + O2 (g) (l) H = O = 2 4 H = O = 2 4 2 1 2 Only the coefficients can be changed!

Balancing Tips Always balance non-Oxygen’s & Hydrogen’s first (ex. Chlorine) Then balance Hydrogens Balance Oxygens Last

Balancing Practice! P4 + O2 → P2O5 Ca2Si + Cl2 → CaCl2 + SiCl4 Si + CO2 → SiC + SiO2 2 Si + CO2 → SiC + SiO2 C3H8 + O2 → CO2 + H2O C3H8 + 5 O2 → 3 CO2 + 4 H2O

Overview of Major Chemical Reaction Types Synthesis Decomposition Single-Replacement Double-Replacement Combustion

1. Synthesis Reactions + H2 H2O O2  (g) (l) O O O O Two substances combine to make one Synthesis means “to make” + H2  H2O O2 (g) (l) O O H H O H O H

SYNTHESIS A + B  AB Na + Cl2  NaCl

2. Decomposition Reactions One substance breaks down into 2 Decomposition means “to break down” or “decay” + NH3  H2 (g) (l) N2 H H H H N N H H

Decomposition AB  A + B NaCl  Na + Cl2

one element replaces another in a compound 3. SINGLE REPLACEMENT one element replaces another in a compound AB + C  AC + B

Single Replacement Reaction

Single Replacement AB + C  AC + B or CB + A NaBr + Cl2  NaCl + Br2

Both elements in two compounds switch places 4. DOUBLE REPLACEMENT Both elements in two compounds switch places AB + CD  AD + CB

NaBr + Pb2S3  Na2S + PbBr3 Double Replacement KOH + BaSO4 K2SO4 + Ba(OH)2 KOH + BaSO4

+ + + 5. Combustion Reactions CH4 H2O O2 CO2 C2H4 H2O O2 CO2 C6H12O6 A hydrocarbon reacts with oxygen gas to produce carbon dioxide and water vapor Combustion means to “burn in oxygen” + CH4  H2O O2 CO2 + C2H4  H2O O2 CO2 + C6H12O6  H2O O2 CO2