Balancing Chemical Equations and Types of Chemical Reactions

1. Balancing Chemical Equations and Types of Chemical Reactions 09.24 & 09.25 2012 Boon Chemistry

2. Catalyst • Take out your Homework. • Identify the reactants and products in the following chemical reaction equations: • 2 Mg (s) + O2 (g) 2 MgO (s) • CH4 (g) + 2 O2 (g)  CO2 (g) + 2 H2O (l) • Write the chemical reaction equation for the following description: • Hydrogen gas and oxygen gas combine to form liquid water.

3. Catalyst Answers: • Take out your Homework. • Identify the reactants and products in the following chemical reaction equations: • 2 Mg (s) + O2 (g) 2 MgO (s) • CH4 (g) + 2 O2 (g)  CO2 (g) + 2 H2O (l) • Reactants are on the left and products on the right of the arrow. • Write the chemical reaction equation for the following description: • Hydrogen gas and oxygen gas combine to form liquid water. • 2 H2(g) + O2 (g) 2 H2O (l)

4. Objectives • I can compare and contrast different types of chemical reactions. • I can define and identify a balanced chemical equation. • I can balance simple chemical equations.

5. Agenda • Catalyst (10) • Balancing Notes & HW Review (20) • Group Work: Balancing Chemical Equations. (40) • Types of Chemical Equations Reading Activity (40) • Group Work (20) • Presentations & Debrief (20) • Exit Slip (10)

6. Why do we balance Chemical Reactions?

7. + H2 O2  H2O (g) (g) (l) O O O H H H H H H O H H Law of Conservation of Mass • Matter cannot be created or destroyed in a chemical reaction • The number of atoms on the reactant side must equal the atoms of the products Unbalanced! Balanced!

8. Balanced Chemical Equations • A chemical equation is “balanced” when there are the same number of atoms of each element on both sides of the arrow. NaHCO3 (s) + HC2H3O2 (aq) èNaC2H3O2 (aq) + CO2 (g) + H2O (l) Is it balanced?

9. Is it balanced? Practice • Determine the number of atoms of each element in the reactants and products. Then, state whether the equation is balanced. • P4 + O2 → P2O5 • C3H8 + O2 → CO2 + H2O • Ca2Si + Cl2 → CaCl2 + SiCl4 • Si + CO2 → SiC + SiO2 Not balanced. Not balanced. Not balanced. Not balanced.

10. coefficient + H2 O2  H2O (g) (g) (l) Balancing Equations 2 2 • Only the coefficients can be changed! H = O = 2 4 H = O = 2 4 2 1 2

11. Balancing Tips • Always balance non-Oxygen’s & Hydrogen’s first (ex. Chlorine) • Then balance Hydrogens • Balance Oxygens Last

12. Balancing Practice! • P4 + O2 → P2O5 P4 + 5 O2 → 2 P2O5 • C3H8 + O2 → CO2 + H2O C3H8 + 5 O2 → 3 CO2 + 4 H2O • Ca2Si + Cl2 → CaCl2 + SiCl4 Ca2Si + 4 Cl2 → 2 CaCl2 + SiCl4 • Si + CO2 → SiC + SiO2 2 Si + CO2 → SiC + SiO2

13. Group Work: Balancing Equations • Instructions: • Work with the person next to you. • You have two worksheets to work on. • 1. “Is it balanced?” Determine whether the chemical equation is balanced by counting atoms in the reactants and products. • 2. “Balancing Act” Practice balancing equations. • What you do not finish is homework. • Ms. Boon will stamp your work when you are done. • Once you have a stamp, you may check your answers on the posted answer sheet.

14. Balancing Act Notes • Atoms are not created or destroyed during a chemical reaction. • Scientists know that there must be the same number of atoms on each side of the equation. • To balance the chemical equation, you must add coefficients to the different parts of the equation.

15. Chemical Reactions Reading • You will work in groups of four or five at your table. • Fold a sheet of paper into four squares. • Label each square: • Synthesis reaction • Decomposition reaction • Single Replacement Reaction • Double Replacement Reaction • You will be assigned one reaction. • Read the section on that reaction, define it, give an example, and draw a picture in your chart. (7 min) • Take turns sharing with your group. (8 min) • Take notes on the other 3 reactions. • If you finish early, read the entire article.

16. + H2 O2  H2O (g) (g) (l) H H O O H H H H H H 1. Synthesis Reactions • Two substances combine to make one • Synthesismeans “to make” O O

17. A + B  AB SYNTHESIS Na + Cl2 NaCl

18. NH3 (l) N2 + H2  (g) (g) 2. Decomposition Reactions • One substance breaks down into 2 • Decompositionmeans “to break down” or “decay” H H H H N N H H

19. AB  A + B Decomposition NaCl  Na + Cl2

20. one element replaces another in a compound 3. SINGLE REPLACEMENT AB + C  AC + B

21. Single Replacement Reaction

22. Single Replacement AB + C  AC + B or CB + A NaBr + Cl2 NaCl + Br2

23. 4. DOUBLE REPLACEMENT Both elements in two compounds switch places AB + CD  AD + CB

24. Double Replacement NaBr + Pb2S3 Na2S + PbBr3 K2SO4 + Ba(OH)2 KOH + BaSO4

25. CH4 C2H4 + + O2 O2 CO2 CO2 + + H2O H2O   C6H12O6 + O2 CO2 + H2O  5. Combustion Reactions • A hydrocarbon reacts with oxygen gas to produce carbon dioxide and water vapor • Combustionmeans to “burn in oxygen”

26. Exit Slip! Balance and Identify the Type of Reaction. • Mg + O2 MgO • C3H8 + O2  CO2 + H2O • Na + Cl2  NaCl • C6H6  C + H2 • FeO + CO2  FeCO3

27. Homework • Read pp. 271-274 • Do problems pp. 271 #1-3, pp. 298 #1, 2, 3, 5, 6, 7