This document discusses chemical reactions. It defines different types of chemical reactions including synthesis, combustion, decomposition, single replacement, and double replacement reactions. It provides examples of each type of reaction and gives steps for writing and balancing chemical equations. Key points covered include identifying evidence of a chemical reaction, writing word and skeleton equations, and using coefficients to balance equations so matter is conserved.

1. CH 10 CHEMICAL REACTIONS

2. What’s the center or target? Building Blocks Putting them together Rearranging them Disassembling them

3. Chemical Reactions

4. Evidence of Chemical Reaction 1. Color change 2. Energy change: absorbed or released

5. 3. Odor changes or production 4. Gas production 5. Precipitate formation

6. Chemical equations are used to write/ represent chemical reactions Show Reactants : the starting substances Show Products : resulting or ending substances Use yield ( ->) sign instead of equal sign (=) Reactants Products

7. Word equation : uses words Setup: Reactant 1 + Reactant 2  Product 1 Ex: Iron(s) + Chlorine(g)  Iron(III) Chloride(s) Skeleton equation: uses formulas Ex: Fe(s) + Cl 2 (g)  Fe Cl 3 (s) Chemical equation : balanced equation Shows matter is conserved during a reaction (Law of Conservation of Mass) Ex: 2 Fe(s) + 3 Cl 2 (g)  2 Fe Cl 3 (s) Bolded NUMBER in FRONT are called Coefficients

8. Write the skeleton equation Count the atoms of each element in the reactants Count the atoms of each element in the products Change the coefficients to make both sides of the equation the equal (=) (DO NOT CHANGE SUBSCRIPTS) Write the coefficient(s) in the lowest ratio possible Check your work Ex: H 2 (g) + O 2 (g)  H 2 O(g) Balanced: 2 H 2 + O 2 (g)  2 H 2 O(g) Practice website www.chem.vt.edu/RVGS/ACT/notes/scripts/bal_eq1.html Steps to Balance a Chemical Equation

9. Examples Hydrogen gas and bromine gas form gaseous hydrogen bromide H 2 + Br 2  HBr Balanced: H 2 + Br 2  2 HBr Balancing hints: When odd numbers of oxygen needed use a fraction, then multiply by two Al + O 2  Al 2 O 3 2 Al + O 2  Al 2 O 3 need three oxygens (odd number) 2 Al + 1.5 O 2  Al 2 O 3 fractions/ decimals cannot be left as coefficients 4 Al + 3 O 2  2 Al 2 O 3 Whole equation multiplied by two to get rid of decimals or fractions Try the following: C 2 H 6 + O 2  CO 2 + H 2 O

10. Examples/ hints cont. When balancing with polyatomic ions found both in the reactants and products, replace the ions by a variable. Fe 2 O 3 + H 2 SO 4  Fe 2 (SO 4 ) 3 + H 2 O Fe 2 O 3 + H 2 X  Fe 2 ( X ) 3 + H 2 O Fe 2 O 3 + 3 H 2 X  Fe 2 ( X ) 3 + 3 H 2 O Fe 2 O 3 + 3 H 2 SO 4  Fe 2 (SO 4 ) 3 + 3 H 2 O Balancing with elements that appear more than twice in different formulas ( leave for last! ) CO 2 + H 2  C H 4 + H 2 O hydrogen appears more than twice CO 2 + H 2  CH 4 + 2 H 2 O balance C and O CO 2 + 4 H 2  CH 4 + 2 H 2 O

11. Synthesis – formation, combining Combustion - burns in air, reaction with O 2 Decomposition – breaking down into components Single-Replacement – exchange of 1 element in a compound Double-Replacement – exchange of ions b/w 2 compounds AB -> A + B AB + CD -> AD + BC

12. Synthesis Reaction Chemical reaction in which two or more substances combine to form one single product. A + B  AB Ex: 2Na(s) + Cl 2 (g)  2NaCl(s) 4Fe(s) + 3O 2 (g)  2Fe 2 O 3 (s) Combustion Reaction Oxygen combined with a substance releasing energy in the form of light and heat Many combustion reactions are also synthesis reactions A + O 2  AO Ex: 2H 2 (g) + O 2  2H 2 O(g)

13. Decomposition reactions Only one compound Breaks down into 2 or more compounds or elements Setup: AB  A + B Often requires an energy source (i.e. heat, light, electricity) Ex: NH 4 NO 3 (s)  N 2 O(g) + 2H 2 O(g) The above reaction occurs when the reactant is heated Replacement Reactions involve the replacement of an element in compound 2 kinds of replacement reactions: Single Double

14. Single Replacement reactions When atoms of one element replace the atoms of another element in a compound Setup: Whether or not a metal will replace another metal or any other substance depends on the reactivity it has A+ BX  AX + B

15. Double Replacement reactions Invovles the exchange of ions between 2 compounds Setup: AX + BY  AY + BX If a solid is produced during the reaction it is called a precipitate

16. Practice – Classify the following reactions

17. Practice – Classify the following equations & Balance them Cl 2 + KBr  KCl + Br 2 Ag 2 O  Ag + O 2 Na + Cl 2  NaCl PbCl 2 + Li 2 SO4  PbSO 4 + LiCl C 6 H 12 O 6 + O 2 -> C O 2 + H 2 O