1. Reactions and Stoichiometry
Chapters 11-12

2. Reactions
Reactants
Products

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

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 NOT change chemistry (compounds, subscripts)
Only change coefficients (big numbers in front of chemicals)
Coefficients can only be whole numbers
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
2Mg + O2  2MgO

10. Decomposition
Chemical change in which a single compound breaks down into two or more simpler products
1 reactant
NaHCO3  NaOH + CO2

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

12. Double Replacement
Chemical change involving an exchange of positive ions between compounds
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

16. 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

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

18. 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

19. 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

20. Table F

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

23. Stoichiometry
Goal
The role of coefficients in balanced formula equations
Mole ratios in a balanced formula
Mole-mole stoichiometry problems

24. Stoichiometry
Calculations of quantities in chemical reactions

25. Food Example 8
amount X 4 2 1 10
ratio
X = 20 pancakes
How many pancakes can be made with 8 cups flour, excess eggs and milk?

26. Process for Solving Balance reaction
Copy coefficients from reaction into ratio row
Place numbers from question in row above ratio row (Setting up proportion)
Solve for X using a proportion

27. Food Example How many eggs are needed to make 25 pancakes? 25 X 4 2 1
amount X 4 2 1 10
ratio
X = 5 eggs
How many eggs are needed to make 25 pancakes?

28. Chemical Example 6 X
amount = 1 3 2
ratio
X = 4 mol NH3
How many moles of NH3 can be made with 6 moles H2 and excess N2?

29. Chemical Example X 7
amount 1 3 2
ratio
X = 3.5 mol N2
How many moles of N2 are needed to produce 7 moles of NH3?

30. Chemical Example X 9
amount 1 5 3 4
ratio
X = mol O2
How many moles of O2 are needed to produce 9 moles of H2O?

32. 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

33. Example 6 X
amount
ratio 1 3 2
91.8
X =183.6 kJ
How much energy is produced when 6 moles H2 reacts with excess N2?