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C.1 Notes: Atom Inventory & Balancing Equations. Reactants --> Products. #\'s & types of atoms in Reactants. #\'s & types of atoms in Products. =. Conservation. Atoms are FOREVER!!.

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c 1 notes atom inventory balancing equations

C.1 Notes: Atom Inventory& Balancing Equations

Reactants --> Products

Rev 6/3/04

conservation

#\'s & types of atoms

in Reactants

#\'s & types of atoms

in Products

=

Conservation

Atoms are FOREVER!!

  • Law of Conservation of Matter—in a chemical reaction, matter can neither be created nor destroyed – just rearranged.
  • The numbers & kinds of atoms present in the products are the same as those in the reactants.
  • Balanced equations illustrate this law.
atom inventory

O

O

O

H

H

H

H

H

H

Atom Inventory
  • List atoms in reactants and products under the arrow
  • Determine the number of each atom.
  • Subscripts—show a ratio of atoms to each other in a particular compound.

H2O =‘s 2 hydrogens bonded to 1 oxygen

  • Subscripts are NEVER changed when balancing!
  • Coefficients—(#’s in front of compound) show how many of each compound is present. 2H2O =‘s 2 waters
slide4

Example of Atom Inventory:

CH4 + 2 O2 CO2 + 2 H2O

ReactantsProducts

____ C ____

____ H ____

____ O ____

1

1

4

4

4

4

What does it mean if there is no coefficient in front of the compound?

Is this equation balanced?

Yes!!!

It is an implied “1”!

steps to balance
Steps to Balance
  • Do an atom inventory.
  • Balance by using coefficients to show multiple number of elements or compounds.

(NEVER change subscripts to balance…is H2Othe same as H2O2?If so, would you like a big cold glass of hydrogen peroxide?!)

(Coefficients only inserted in front of compound, never split compound or the ratio would D)

  • Recount both sides.
example h 2 g o 2 g h 2 o l
Example:H2 (g) + O2 (g)  H2O (l)

2

2

  • Atom Inventory:

Reactants Products

2 H 2

2 O 1

  • Insert coefficients to balance

3. Double check to make sure it is all BALANCED!

4

4

2

slide7

Balance

Al + O2 Al2O3

4

3

2

ReactantsProducts

____ Al ____

____ O ____

1

-- 4

-- 4

2

2

-- 6

-- 6

3

Do an atom inventory

No

Is this equation balanced?

Use coefficient to multiplyCOMPOUND with element in it by # that balances it.

additional rules
Additional Rules
  • Polyatomic ions, (like NO3- and CO32-) that appear on both sides of equation should be balanced as units rather than balancing their atoms individually
  • AgNO3+ Cu ---> Cu(NO3)2 + Ag
  • Balance atoms in pure elements w/ no subscripts last
  • Recount all atoms one last time to be sure you are correct!

2

2

balancing equations
Balancing Equations
  • For labs, demos, and whenever possible, indicate the states of each element or compound.
    • (s) solid (g) gas
    • (l) liquid (aq) aqueous
  • Diatomic Elements?
  • H O F Br I N Cl
  • Remember these elements need a subscript of 2 if in elemental state. If in compound then criss- cross charges to get subscripts
practice
Practice

2 NaCl + H2SO4  Na2SO4 + 2 HCl

  • NaCl + H2SO4  Na2SO4 + HCl
  • BaF2 + Al(OH)3  Ba(OH)2 + AlF3
  • 3 BaF2 + 2 Al(OH)3  3 Ba(OH)2 + 2 AlF3
  • C2H6 + O2  CO2 + H2O
  • 2C2H6 + 7O2  4CO2 + 6H2O

(had to double everything to balance oxygen)

balanced equations show proportions
Balanced Equations show Proportions
  • Coefficients show how many of each compound reacts with, or creates another substance.
  • Does that mean ONLY 2 hydrogen molecules will react with only 1 oxygen molecule?
  • NO!! Could be 250 H2 react with 125 O2
example 2 h 2 g o 2 g 2 h 2 o l
Example:2 H2 (g) + O2 (g)  2 H2O (l)
  • 2 H2 molecules produce 2 H2O molecules
  • 1 O2 molecule produces 2 H2O molecules
  • 2 H2 molecules react with 1 O2 molecules
example 2 h 2 g o 2 g 2 h 2 o l1
Example:2 H2 (g) + O2 (g)  2 H2O (l)
  • Does that mean ONLY 2 hydrogen molecules will react with only 1 oxygen molecule?
  • NO!! Could be 250 H2 react with 125 O2
types of chemical reactions
Types of Chemical Reactions

Examples

A + B  AB

N2 + 3H2 2NH3

  • Synthesis
  • Decomposition
  • Single replacement (displacement)
  • Double replacement (displacement)
  • Combustion

H2O2  H2 + O2

AB  A + B

A + BC  AC + B

Zn + 2HCl  ZnCl2 + H2

A + BD BA + D

AB + CD  AD + CB

NaCl + AgNO3 NaNO3 + AgCl

CxHy + O2 CO2 + H2O

CH4 + 2O2 CO2 + 2H2O

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