1. Reactions and Stoichiometry
Chapters 11-12

2. General Reaction Format
Reactants
Products
Starting Material
Ending Material
Science equivalent of Math’s =

3. Balancing Reactions
Reactions must maintain conservation of mass, charge, and energy
Reactants and Products must have the same number of atoms of each element
2H2 + O2  2H2O
Total mass of Reactants must equal the total mass of Products

4. Balancing Reactions
Reactions must maintain conservation of mass, charge, and energy
Reactants must have the same total charge as Products
Cu Fe+3  Cu Fe+2

5. Balancing Reactions To balance a reaction:
Do Chemistry (determine products)
Do NOT change chemistry (compounds, subscripts)
Only change coefficients (whole numbers in front of chemicals)
Must be reduced
2H2 + O2  2H2O

6. Balancing Reactions 4Na + O2  2Na2O 2Al + 3Br2  2AlBr3
4Ni + 3O2  2Ni2O3
2HNO3 + Ca(OH)2  Ca(NO3) H2O

8. Reaction Types Synthesis Decomposition Single Replacement
Double Replacement
Combustion

9. Synthesis
Chemical change in which two or more substances react to form a single new substance (1 product)
Also called Combination (old)
A + B  AB
2Mg + O2  2MgO

10. Decomposition
Chemical change in which a single compound breaks down into two or more simpler products
1 reactant
AB  A + B
2NaCl  2Na + Cl2

11. Single Replacement
Chemical change in which one element replaces a second element in a compound
Metal replaces metal (hydrogen included)
Nonmetal replaces nonmetal
A + BC  AC + B
A + BC  BA + C
Zn + 2HCl  ZnCl2 + H2

12. Double Replacement
Chemical change involving an exchange of positive ions between compounds
AB + CD  AD + CB
AgNO3 + NaCl  NaNO3 + AgCl

13. Combustion
Chemical change in which an element or a compound reacts with oxygen, often producing energy in the form of heat and light
2Mg + O2  2MgO

14. Combustion
Complete combustion of a hydrocarbon produces carbon dioxide and water
2C2H O2  4CO H2O

15. Chemical Changes Indications of a chemical change Transfer of Energy
Change in temperature
Production of Light
Formation of a gas
Formation of a precipitate
Change in color

17. Spontaneous Reactions
A single replacement reaction will only occur if:
The single element in the reactants is more active than the element it replaces in the compound

18. Table J The more active element: Does not want to be alone
Wants to be combined with someone else

19. Spontaneous or not? ZnCO3 + Mg  MgCO3 + Zn PbSO4 + Mn  MnSO4 + Pb
3KNO3 + Al  Al(NO3)3 + 3K
2HCl + Zn  ZnCl2 + H2
2NaBr + I2  2NaI + Br2
YES
YES NO
YES NO

20. Spontaneous Reactions
A double replacement reaction will only occur if:
A precipitate (solid) is produced
A liquid is produced
H2O(l)
A gas is produced

21. Table F

22. Spontaneous or not? NaCl + AgNO3  NaNO3 + AgCl
K2CO3 + MgSO4  K2SO4 + MgCO3
NH4OH + NaNO3  NaOH + NH4NO3
Yes
Yes No

24. Stoichiometry
Calculations of quantities in chemical reactions

25. Food Example 8 X
How many pancakes can be made with 8 cups flour, excess eggs and milk?
X = 20 pancakes

26. Process for Solving Determine Reaction Products Balance reaction
Place numbers from question above coefficients in reaction (Setting up proportion)
Solve for X using a proportion

27. Food Example How many eggs are needed to make 25 pancakes? X 25
X = 5 eggs

28. Chemical Example 6 X
How many moles of NH3 can be made with 6 moles H2 and excess N2?
X = 4 mol NH3

29. Chemical Example X 7
How many moles of N2 are needed to produce 7 moles of NH3?
X = 3.5 mol N2

30. Chemical Example X 9
How many moles of O2 are needed to produce 9 moles of H2O?
X = mol O2

32. Conservation of Energy
Reactions must maintain conservation of energy
Energy term written in reaction

33. Endo/Exothermic Endothermic – Energy is absorbed
Energy term is on the left side
Exothermic – Energy is released
Energy term is on the right side
Treat just like a coefficient

34. Example 6 X
How much energy is produced when 6 moles H2 reacts with excess N2?
X =183.6 kJ