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Chemical Equations

Chemical Equations. And how to balance them. What is a Chemical Equation?. A chemical equation is a symbolic representation of a chemical reaction. Indications of a Chemical Reaction. Evolution of heat and light Production of a gas Formation of a precipitate Color change.

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Chemical Equations

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  1. Chemical Equations And how to balance them

  2. What is a Chemical Equation? A chemical equation is a symbolic representation of a chemical reaction

  3. Indications of a Chemical Reaction Evolution of heat and light Production of a gas Formation of a precipitate Color change

  4. All chemical reactions are written in the following format: Reactants Products

  5. Law of Conservation of Mass Atoms are neither created nor destroyed in ordinary chemical reactions. equations must be balanced use coefficients Coefficient – small whole number that appears in front of a formula in a chemical equation (1 is assumed)

  6. More on equations…. Each formula in an equation shows the physical state of the compound it represents 2HCl(aq)+Ca(OH)2(aq) CaCl2(s)+2H2O(l) (s) – solid (l) – liquid (g) – gas (aq) – aqueous (dissolved in water)

  7. More on equations… • A catalyst speeds up a reaction without being changed • written over the arrow in chem. eq. reactants catalyst products Look on wiki for other equation symbols you should know . . . ... Or look at chart on pg. 246 of your book for other equation symbols

  8. Diatomic Molecules • Some elements that are gases in their elemental form exist as diatomic molecules, or two atoms bonded together • Halogens • Hydrogen • Oxygen • Nitrogen • Br2, H2, O2, N2, Cl2, I2, F2 (brother honclif, lucky 7)

  9. Writing equations • reactants on left of arrow • products on right of arrow • plus sign between each compound • write correct states of matter (s,l,g,aq)

  10. Balancing • Each side of the arrow must have the same # of each element • Check to make sure compounds are written correctly • You CANNOT balance an equation until all compounds are written correctly • Balance equation using coefficients

  11. Balancing • Get yourself an unbalanced equation. Given or figured out (must have correct formulas!) • Draw boxes around all the chemical formulas. Never, ever, change anything inside the boxes. Ever. • Make an element inventory. Keep it current throughout the whole problem. • Write numbers in front of each of the boxes until the inventory for each element is the same both before and after the reaction. Whenever you change a number, update the inventory

  12. Balancing NH3(g) N2(g) + H2(g) 1 N 2 N 3 H 2 H 2NH3(g) N2(g) + H2(g) 2 N 2 N 6 H 2 H 2NH3(g) N2(g) + 3H2(g) 2 N 2 N 6 H 6 H This equation is now balanced and the coefficients are in the simplest form.

  13. Balance the following equations as a class Al + O2 Al2O3 CO2 + H2 CH4 + H2O C2H6 + O2 CO2 + H2O Fe2O3 + H2SO4 Fe2(SO4)3 + H2O

  14. Balance the following equations as a class 2Al + 3O2 2Al2O3 CO2 + 4H2 CH4 + 2H2O 2C2H6 + 7O2 4CO2 + 6H2O Fe2O3 + 3H2SO4 Fe2(SO4)3 + 3H2O

  15. Please balance at your desk Mg (s) + O2 (g)MgO(s) K2O + H2O KOH C3H8 + O2 CO2 + H2O Al + CuO Al2O3 + Cu Fe2(SO4)3 + KSCN  K3Fe(SCN)6 + K2SO4

  16. Please balance at your desk 2Mg (s) + O2 (g)2MgO (s) K2O + H2O 2KOH C3H8 + 5O2 3CO2 + 4H2O 2Al + 3CuO  Al2O3 + 3Cu Fe2(SO4)3 + 12KSCN  2K3Fe(SCN)6 + 3K2SO4

  17. Balancing Tips! You may only put numbers in front of molecules, never changethe subscripts!! Al + O2 Al2O3 Al2 + O3 Al2O3 2Al + 3O2 2Al2O3

  18. Balancing Tips! You can reduce OR multiply C2H6 + O2 CO2 + H2O C2H6 + 7/2O2 2CO2 + 3H2O 2C2H6 + 7O2 4CO2 + 6H2O

  19. Balancing Tips! Start with large formulas or elements that appear only once on each side Fe2(SO4)3 + KSCN  K3Fe(SCN)6 + K2SO4 Make sure this one balances first

  20. When balancing equations, keep in mind: Balance polyatomic ions as one item Fe2(SO4)3+ KSCN  K3Fe(SCN)6 + K2SO4 Fe2X3+ 12KY  2K3FeY6 + 3K2X

  21. When balancing equations, keep in mind: Balance elements and diatomic elements last Oxygen and hydrogen last (usually) Al + 3CuO  Al2O3 + Cu 2Al + 3CuO  Al2O3 + 3Cu Balance these first Balance these second

  22. Writing Equations from Words Hydrogen gas and oxygen gas combine to form liquid water. H2 , O2 , H2O H2(g) + O2(g)  H2O(l) 2 H 2 H 2 O 1 O H2(g) + O2(g)  2H2O(l) 2 H 4 H 2 O 2 O 2H2(g) + O2(g)  2H2O(l) 4 H 4 H 2 O 2 O The equation is balanced and in it’s simplest form

  23. Try these… When calcium carbonate is heated, calcium oxide and carbon dioxide are produced. Solid sodium hydrogen carbonate reacts with hydrochloric acid to produce aqueous sodium chloride, water, and carbon dioxide gas. Aluminum metal reacts with oxygen in the air to form aluminum oxide.

  24. Try these… When calcium carbonate is heated, calcium oxide and carbon dioxide are produced. CaCO3  CaO + CO2 Solid sodium hydrogen carbonate reacts with hydrochloric acid to produce aqueous sodium chloride, water, and carbon dioxide gas. NaHCO3 + HCl NaCl + H2O + CO2 Aluminum metal reacts with oxygen in the air to form aluminum oxide. Al + O2  Al2O3

  25. Writing Words from Equations K2O + H2O 2KOH Potassium oxide combined with water makes potassium hydroxide. 2C2H6 + 7O2 4CO2 + 6H2O Ethane combusts in the presence of oxygen to form carbon dioxide and water 2Al + 3CuO  Al2O3 + 3Cu Aluminum and copper (II) oxide make aluminum oxide and copper 2NH3(g) N2(g) + 3H2(g) Nitrogen gas and hydrogen gas are formed when ammonia decomposes.

  26. Try These . . . Fe2(SO4)3 + 12KSCN  2K3Fe(SCN)6 + 3K2SO4 CO2 + 4H2 CH4 + 2H2O HCl + Ca(OH)2 CaCl2 + H2O 2KClO3(s) --> 2KCl(s) + 3O2(g)

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