Chemical Equations
Chemical Equations
• Reactants – the substances that exist before a chemical
change (or reaction) takes place.
• Products ...
Showing Phases in
Chemical Equations
Solid Phase – the substance is relatively rigid and has a definite
volume and shape. ...
Additional Symbols Used in Chemical Equations
“Yields”; indicates result of reaction
Used to indicate a reversible reactio...
Additional Symbols Used in Chemical Equations
Alternative to (g), but used only to indicate a gaseous product
Reactants ar...
Describing a Chemical Reaction
Indications of a Chemical Reaction
– Evolution of heat, light, and/or sound
– Production of...
Chemical Equations
Depict the kind of reactants and products
and their relative amounts in a reaction.
4 Al(s) + 3 O2(g) 2...
Chemical Equations
Because the same atoms are present
in a reaction at the beginning (reactants)
and at the end (products)...
Chemical Equations
Because of the principle of the conservation
of mass, all equations must be balanced.
There must be the...
?
Visualizing a Chemical Reaction
Na + Cl2 NaCl
___ mole Cl2 ___ mole NaCl___ mole Na
2
10 5 10
2
10 5 10
Balancing Chemical Equations
Balanced Equation – one in which the number of atoms of
each element as a reactant is equal t...
Balancing Chemical Equations
• Write a word equation for the reaction.
• Write the correct formulas for all reactants
and ...
Balancing Chemical Equations
Other examples
NO(g) + O2(g)  NO2(g) is it balanced?
Is this balanced? NO(g) + O(g)  NO2(g)...
Balancing Chemical Equations
An important point to remember
2 NO(g) + O2(g)  2NO2(g)
The 2 to the left of NO(g) and NO2(g...
(NH4)3PO4 + Mg(OH)2  Mg3(PO4)2 NH4OH?
ammonium phosphate magnesium hydroxide magnesium phosphate ammonium hydroxide
NH4
1...
1) Write a word equation for the reaction.
Write a balanced equation for the reaction between chlorine
and sodium bromide ...
1) Write a word equation for the reaction.
2) Write the correct formulas for all reactants and products.
3) Determine the ...
CH4 + 2 O2  CO2 + 2 H2O
Reactants Products
1 C atom 1 C atom
4 H atoms 4 H atoms
4 O atoms 4 O atoms
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Types of equations

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Types of equations

  1. 1. Chemical Equations
  2. 2. Chemical Equations • Reactants – the substances that exist before a chemical change (or reaction) takes place. • Products – the new substance(s) that are formed during the chemical changes. • CHEMICAL EQUATION indicates the reactants and products of a reaction. REACTANTS  PRODUCTS
  3. 3. Showing Phases in Chemical Equations Solid Phase – the substance is relatively rigid and has a definite volume and shape. NaCl(s) Liquid Phase – the substance has a definite volume, but is able to change shape by flowing. H2O(l) Gaseous Phase – the substance has no definite volume or shape, and it shows little response to gravity. Cl2(g) H2O(s) H2O(l) H2O(g)
  4. 4. Additional Symbols Used in Chemical Equations “Yields”; indicates result of reaction Used to indicate a reversible reaction A reactant or product in the solid state; also used to indicate a precipitate Alternative to (s), but used only to indicate a precipitate A reactant or product in the liquid state A reactant or product in an aqueous solution (dissolved in water) A reactant or product in the gaseous state (s) (l) (aq) (g)
  5. 5. Additional Symbols Used in Chemical Equations Alternative to (g), but used only to indicate a gaseous product Reactants are heated Pressure at which reaction is carried out, in this case 2 atm Pressure at which reaction is carried out exceeds normal atmospheric pressure Temperature at which reaction is carried out, in this case 0 oC Formula of catalyst, in this case manganese (IV) oxide, used to alter the rate of the reaction 2 atm pressure 0 oC MnO2
  6. 6. Describing a Chemical Reaction Indications of a Chemical Reaction – Evolution of heat, light, and/or sound – Production of a gas – Formation of a precipitate – Color change
  7. 7. Chemical Equations Depict the kind of reactants and products and their relative amounts in a reaction. 4 Al(s) + 3 O2(g) 2 Al2O3(s) The numbers in the front are called stoichiometric coefficients. The letters (s), (g), and (l) are the physical states of compounds. reactants product aluminum oxide
  8. 8. Chemical Equations Because the same atoms are present in a reaction at the beginning (reactants) and at the end (products), the amount of matter in a system does not change. The Law of Conservation of Mass Kotz web Chemical Factory 100% 100% 80% 20%
  9. 9. Chemical Equations Because of the principle of the conservation of mass, all equations must be balanced. There must be the same number of atoms of the same kind on both sides. Lavoisier, 1788
  10. 10. ? Visualizing a Chemical Reaction Na + Cl2 NaCl ___ mole Cl2 ___ mole NaCl___ mole Na 2 10 5 10 2 10 5 10
  11. 11. Balancing Chemical Equations Balanced Equation – one in which the number of atoms of each element as a reactant is equal to the number of atoms of that element as a product What is the relationship between conservation of mass and the fact that a balanced equation will always have the same number of atoms of each element on both sides of an equation? Determine whether the following equation is balanced. 2 Na + H2O  2 NaOH + H2 2 Na + 2 H2O  2 NaOH + H2
  12. 12. Balancing Chemical Equations • Write a word equation for the reaction. • Write the correct formulas for all reactants and products. • Determine the coefficients that make the equation balance.
  13. 13. Balancing Chemical Equations Other examples NO(g) + O2(g)  NO2(g) is it balanced? Is this balanced? NO(g) + O(g)  NO2(g) Is this OK? NO(g) + ½ O2(g)  NO2(g)Is this balanced? Is this OK?
  14. 14. Balancing Chemical Equations An important point to remember 2 NO(g) + O2(g)  2NO2(g) The 2 to the left of NO(g) and NO2(g) refers to the number of molecules present in the balanced equation. It is a “multiplier” for every atom in the molecule. The subscript 2 in O2 (g) and NO2(g) refers to the number of atoms of this type that are present in each molecules (or ionic compound).
  15. 15. (NH4)3PO4 + Mg(OH)2  Mg3(PO4)2 NH4OH? ammonium phosphate magnesium hydroxide magnesium phosphate ammonium hydroxide NH4 1+ OH1- + 62 3 Now you try… AlCl3 + Li2CO3  Al2(CO3)3 + LiCl32 6
  16. 16. 1) Write a word equation for the reaction. Write a balanced equation for the reaction between chlorine and sodium bromide to produce bromine and sodium chloride. 2) Write the correct formulas for all reactants and products. 3) Determine the coefficients that make the equation balance. chlorine + sodium bromide  bromine + sodium chloride Cl2 + NaBr  Br2 + NaCl Cl2 + 2 NaBr  Br2 + 2 NaCl
  17. 17. 1) Write a word equation for the reaction. 2) Write the correct formulas for all reactants and products. 3) Determine the coefficients that make the equation balance. aluminum sulfate + calcium chloride  calcium sulfate Al2(SO4)3 + CaCl2  CaSO4 + AlCl3 Write the balanced equation for the reaction between aluminum sulfate and calcium chloride to form a white precipitate of calcium sulfate. Al2(SO4)3 + 3 CaCl2  3 CaSO4 + 2 AlCl3 + aluminum chloride ? ?
  18. 18. CH4 + 2 O2  CO2 + 2 H2O Reactants Products 1 C atom 1 C atom 4 H atoms 4 H atoms 4 O atoms 4 O atoms

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