homer helps with bart’s chemistry homework play this as a slide show to see the balancing in...
TRANSCRIPT
Balancing Chemical Equations, Reaction Kinetics, & Heats of
ReactionsHomer Helps with Bart’s Chemistry
Homework
Play This as a Slide Show to see the Balancing in Action!
To Obey the LAW of Conservation of Matter!!!◦ We must have the same #atoms of each type at
the start & end of a chemical reaction◦ # Reactant atoms = # Product atoms◦ Otherwise we have created or destroyed Matter!◦ Ex: Na + CaF2 NaF + Ca
Na=1 Na=1Ca=1 Ca=1F=2 F=1
We broke the LAW Matter was DESTROYED!!
Why Do we Need to Balance Equations?
Subscripts◦ These are the numbers below the symbol◦ They tell how many atoms are bonded together in one
molecule◦ For example C2H6 has 2C atoms bonded to 6H atoms◦ The subscripts are determined by the valence electrons
◦WE CAN’T CHANGE THE SUBSCRIPT!!◦ We find the subscripts by using:
Bohr Model Lewis Dots Criss-cross /oxidation #
Balancing TipsHH
C C H
HH
H
Coefficients◦ These are the numbers in front of the symbol◦ They tell how many atoms or molecules we have◦ It multiplies the number of atoms or molecules
(including the subscript)◦ Ex: 3Na = 3Na atoms
2 C2H6 = 2x2 = 4C atoms
=2x6 = 12H atoms◦IT IS THE ONLY NUMBER THAT WE CAN CHANGE!!
Balancing tips
Polyatomic Ions◦ Are many atoms bonded together to form an ion◦ Examples
NO3 = nitrate; ion charge = -1 SO4 = sulphate; ion charge = -2 NH4 = ammonium ion; ion charge = +1 CO3 = carbonate; ion charge = -2 PO4 = sulphate; ion charge = -3
◦Count how many polyatomic ions you have when balancing; not the individual atoms Ex: 2HNO3
H=2 and NO3 =2 Not H=2 & N=2 and O=6
Balancing tips
1. Na + MgF2 NaF + Mg
2. Mg + HCl MgCl2 + H2
3. Cl2 + KI KCl + I24. NaCl Na + Cl25. Na + O2 Na2O
6. Na + HCl H2 + NaCl
7. K + Cl2 KCl
8. N2 + H2 NH3
9. CH4 + O2 CO2 +H2O
10. Al + Fe2O3 Al2O3 +Fe
Practice Problems
◦ Called Reaction Kinetics◦ Reactions happen when the reactant atoms collide with enough
energy to form new product molecules Factors that influence the rates of chemical reactions:
Concentration More particles present in a given volume increases the probability of
collisions Temperature
Increases the vibrational movement of the atoms which increases the probability of collisions
Also increases the energy of the collisions Surface Area
Increases the number of atoms exposed to collisions Ex: grinding up a reactant into a powder
Catalysts Increase reaction rates, but are not consumed in the reaction Collect the reactant atoms and bring them close together so they can react
Rates of Chemical Reactions
Reactions either absorb (endothermic) or release heat (exothermic)
This has to do with the bond energy◦ It takes energy to break bonds◦ Energy is released when bonds form because an
atom has lower energy when it gains an electron
Exothermic & Endothermic Reactions
Exothermic reactions release energy Exo means “out” & thermic means heat
(“Heat Out”) The products have more energy than the
reactants When the products form, they release more
energy than it took to break the reactant bonds
HEAT IS RELEASED