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BALANCING CHEMICAL EQUATIONS. Chemical reaction is a process in which one or more substances are converted into new substances with different physical and chemical properties. Signs of a Chemical Reaction. Evolution of heat and light Formation of a gas Formation of a precipitate

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Presentation Transcript
slide2

Chemical reaction is a process in which one or more substances are converted into new substances with different physical and chemical properties.

signs of a chemical reaction
Signs of a Chemical Reaction
  • Evolution of heat and light
  • Formation of a gas
  • Formation of a precipitate
  • Color change
law of conservation of mass
Law of Conservation of Mass
  • mass is neither created nor destroyed in a chemical reaction
  • total mass stays the same
  • atoms can only rearrange

4 H

2 O

4 H

2 O

36 g

4 g

32 g

rules for balancing equations

RULES FOR BALANCING EQUATIONS.

1.Write reactants on left.

2. Write products on right.

3. Arrow between reactants and products.

4. Separate formulas with +.

chemical equations
Chemical Equations

A+B  C+D

REACTANTS

PRODUCTS

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5. Determine CORRECT formulas for products and reactants.

6. Count atoms on both sides.

7. Balance using coefficients.

8. Check to see if balanced. Total atoms = subscript x coefficient.

9. Make sure coefficients are the lowest whole number ratio.

hints
Hints:
  • Treat polyatomic ions as a unit. (OH-,NO3-,CO3-2, SO4-2)
  • Balance H & O last if H2O is present.
  • Don’t forget the diatomic elements.
types of reactions1
Types of Reactions
  • Combination or synthesis: reaction of two or more reactants to a single substance.
  • A + B ---> AB
synthesis
Synthesis

H2(g) + Cl2(g)  2 HCl(g)

decomposition
Decomposition

2 H2O(l)  2 H2(g) + O2(g)

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Single Replacement: Atoms of an element replace atoms of a second element in a compound.
  • Free element becomes an ion and the ion becomes a neutral atom.
  • Metal replaces metal. Halogen replaces halogen.
  • A + BC ---> B + AC
  • Will replace anything below it on an activity series.
single replacement
Single Replacement

Cu(s) + 2AgNO3(aq)  Cu(NO3)2(aq) + 2Ag(s)

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Double Replacement: Exchange of positive ions between two compounds.
  • AB + CD ---> AD + CB
  • Will only happen if one of the products is removed from the solution.
  • Precipitate forms.
  • Gas is formed.
  • Water is formed.
double replacement
Double Replacement

Pb(NO3)2(aq) + K2CrO4(aq)  PbCrO4(s) + 2KNO3(aq)

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Combustion: oxygen reacts with another substance.
  • X + O2 ---> XO
  • Hydrocarbons + oxygen ---> carbon dioxide + water.
  • CxHy + O2 ---> CO2 + H2O
dissolving equations
Dissolving Equations
  • From the name of the substance, write its formula.
  • After the formula of the substance, place an (s), meaning solid, and an arrow.
  • After the arrow write the formulas of the two ions contained in the substance. Copy these formulas directly from the ion chart and remember to write the ion charge.
  • Separate the individual ion formulas with a + sign and add (aq) for aqueous after each ion.
  • Balance the equation by deciding how many of each ion are released from one molecule of the solid.
net ionic equation
Net Ionic Equation
  • Net ionic equation includes only those compounds and ions that undergo a chemical change in a reaction in an aqueous solution.
steps to obtain net ionic equation
STEPS TO OBTAIN NET IONIC EQUATION
  • Write names of reactants and products in WORD EQUATION form. (Double replacement)
  • Change all four names to formulas.
  • Balance. This gives you a balanced non-ionic equation.
  • Use solubility table to decide whether each substance is soluble or insoluble.
slide33
Change equation to Total Ionic form. Insoluble substances are written as molecules followed by (s). Soluble substances are written by separating ions with + signs, including ion charge, and (aq). Be sure to carry coefficients to keep the equation balanced.

Determine which ions in the total ionic equation are spectator ions.

Spectator ions are those ions which appear in the same form in reactants and products.

Write Net Ionic equation by eliminating spectator ions from the total ionic equation.

slide34
Copper (II) nitrate + Sodium hydroxide yields Copper(II) hydroxide + Sodium nitrate
  • Cu(NO3)2 + NaOH  Cu(OH)2 + NaNO3
  • Cu(NO3))2(aq)+ 2NaOH(aq) Cu(OH)2(s) + 2NaNO3(aq)
  • Total Ionic Equation
  • Cu+2(aq) +2NO3-(aq)+ 2Na+(aq)+ 2OH-(aq) Cu(OH)2(s) + 2Na+(aq) + 2NO3-(aq)
  • Net Ionic Equation
  • Cu 2+(aq)+ 2OH-(aq) Cu(OH)2(s)