1. Chemical Equations and Chemical Reactions

2. Writing A Chemical Equation
The general format for chemical equations is:
a + b  c + d
The substances on the left side of the equation (a and b in this case) are called the reactant(s).

3. The + sign means “reacts with”.
The  means “produces or yields”.
The substance(s) on the right side of the equation (c and d in this case) are called the product(s).

4. Lets work with the statement Hydrogen gas reacts with oxygen gas to form liquid water.

5. Word Equation:
hydrogen + oxygen  water
Skeleton Equation:
H2(g)+ O2(g)  H2O(l)
Balanced Equation:
___H2(g)+ ___O2(g)  ___H2O(l)
2H2(g)+ O2(g)  2H2O(l)

6. Why must we balance equations?
The Law of Conservation of Mass states that the total mass of reactants is always equal to the total mass of the products. (Lavoisier’s law)
Antoine-Laurent Lavoisier experimenting to determine the composition of water, French engraving, 19th century.

7. Why must we balance equations?
Dalton’s atomic theory states that atoms can not be created or destroyed. Compounds are formed when atoms of different elements combine in fixed proportions.
John Dalton, F.R.S., engraved by Worthington after an 1814 painting by William Allen, published 25 June 1823 in Manchester and London. Note the charts with Dalton's atomic symbols lying on the table. Fisher Collection, Chemical Heritage Foundation.

8. To balance equations numbers called coefficients are put before the formulas. This changes the number of molecules. You cannot add or change subscripts (small numbers). You do not write coefficients of 1 (one).
Sometimes you need to know the state of the chemicals that are involved in a chemical reaction.

9. State
Abbreviation
solid
liquid
gas
aqueous solution

10. State
Abbreviation
solid
(s)
liquid
gas
aqueous solution

11. State
Abbreviation
solid
(s)
liquid
(l)
gas
aqueous solution

12. State
Abbreviation
solid
(s)
liquid
(l)
gas
(g)
aqueous solution

13. State
Abbreviation
solid
(s)
liquid
(l)
gas
(g)
aqueous solution
(aq)

14. Rules For Writing Balanced Chemical Equations
Final Balanced Chemical Equation
2H2(g) + O2(g)  2H2O(l)
Rules For Writing Balanced Chemical Equations
This requires a lot of practice and patience. These rules will not apply in all equations.
1. Write the skeleton equation.

15. Look for a polyatomic ion that appears once on each side of the equation. Balance these first.
Pick single elements that appears on each side. Choose coefficients to balance this element. The terms you balanced in the previous step have to remain balanced. Repeat for any other elements.

16. 4. Check for any term you have not yet looked at
4. Check for any term you have not yet looked at. Adjust the coefficient of the term so that the numbers of the elements appearing in that term are balanced across the whole equation. If you have any fraction coefficients clear them by multiplying. Also, make sure you have the smallest possible coefficients by reducing.
5. Check the equation!

17. Example 1 Word Equation: Skeletal Equation: Na + H2O  NaOH + H2(g)
sodium + water  sodium hydroxide + hydrogen gas
Skeletal Equation:
Na + H2O  NaOH + H2(g)
Balanced Equation:
___Na + ___H2O  ___NaOH +___H2(g)
2Na + 2H2O  2NaOH + H2(g)

18. Example 2 Balanced Chemical Equation 2H2O__ 2Na__ +  2NaOH__ + H2___
2H2O(l) + 2 Na(s)  2NaOH(aq) + H2(g)
Verification
Reactants
Products
2 Na atoms
4 H atoms
2 O atoms

19. Example 2 Word Equation: Skeletal Equation:
copper + silver nitrate  copper(II) nitrate + silver
Skeletal Equation:
___ + ______  ______ + ___
Cu + AgNO3  Cu(NO3)2 + Ag

20. Example 2… Balanced Equation: __Cu +__ AgNO3  __Cu(NO3)2 + __Ag
Balanced Chemical Equation:
Cu__ + 2AgNO3__  Cu(NO3)2__ + 2Ag__
Cu(s) + 2AgNO3(aq)  Cu(NO3)2(aq) + 2Ag(s)

21. Reactants Products Cu(s) + 2AgNO3(aq)  Cu(NO3)2(aq) + 2Ag(s)
Verification
Reactants
Products

22. Reactants Products 1 Cu atom
Cu(s) + 2AgNO3(aq)  Cu(NO3)2(aq) + 2Ag(s)
Verification
Reactants
Products
1 Cu atom

23. Reactants Products 1 Cu atom
Cu(s) + 2AgNO3(aq)  Cu(NO3)2(aq) + 2Ag(s)
Verification
Reactants
Products
1 Cu atom

24. Reactants Products 1 Cu atom 2 Ag atoms
Cu(s) + 2AgNO3(aq)  Cu(NO3)2(aq) + 2Ag(s)
Verification
Reactants
Products
1 Cu atom
2 Ag atoms

25. Reactants Products 1 Cu atom 2 Ag atoms
Cu(s) + 2AgNO3(aq)  Cu(NO3)2(aq) + 2Ag(s)
Verification
Reactants
Products
1 Cu atom
2 Ag atoms

26. Reactants Products 1 Cu atom 2 Ag atoms 2 NO3- ions
Cu(s) + 2AgNO3(aq)  Cu(NO3)2(aq) + 2Ag(s)
Verification
Reactants
Products
1 Cu atom
2 Ag atoms
2 NO3- ions

27. Reactants Products 1 Cu atom 2 Ag atoms 2 NO3- ions
Cu(s) + 2AgNO3(aq)  Cu(NO3)2(aq) + 2Ag(s)
Verification
Reactants
Products
1 Cu atom
2 Ag atoms
2 NO3- ions

28. Example 3 Word Equation:
calcium nitrate + sodium hydroxide  calcium hydroxide + sodium nitrate
Skeletal Equation:
Ca(NO3)2 + NaOH  Ca(OH)2 + NaNO3
Balanced Equation:
__Ca(NO3)2 + __NaOH  __Ca(OH)2 + _NaNO3
Ca(NO3)2 + 2NaOH  Ca(OH)2 + 2NaNO3

29. Balanced Chemical Equation
Ca(NO3)2__ + 2NaOH__  Ca(OH)2__ + NaNO3__
Ca(NO3)2(aq) + 2NaOH(aq)  Ca(OH)2(s) + NaNO3(aq)

30. Ca(NO3)2(aq) + 2NaOH(aq)  Ca(OH)2(s) + 2NaNO3(aq)
Reactants
Products

31. Reactants Products 1 Ca atom
Ca(NO3)2(aq) + 2NaOH(aq)  Ca(OH)2(s) + 2NaNO3(aq)
Reactants
Products
1 Ca atom

32. Reactants Products 1 Ca atom
Ca(NO3)2(aq) + 2NaOH(aq)  Ca(OH)2(s) + 2NaNO3(aq)
Reactants
Products
1 Ca atom

33. Reactants Products 1 Ca atom 2 NO3- ions
Ca(NO3)2(aq) + 2NaOH(aq)  Ca(OH)2(s) + 2NaNO3(aq)
Reactants
Products
1 Ca atom
2 NO3- ions

34. Reactants Products 1 Ca atom 2 NO3- ions
Ca(NO3)2(aq) + 2NaOH(aq)  Ca(OH)2(s) + 2NaNO3(aq)
Reactants
Products
1 Ca atom
2 NO3- ions

35. Reactants Products 1 Ca atom 2 NO3- ions 2 Na atoms
Ca(NO3)2(aq) + 2NaOH(aq)  Ca(OH)2(s) + 2NaNO3(aq)
Reactants
Products
1 Ca atom
2 NO3- ions
2 Na atoms

36. Reactants Products 1 Ca atom 2 NO3- ions 2 Na atoms
Ca(NO3)2(aq) + 2NaOH(aq)  Ca(OH)2(s) + 2NaNO3(aq)
Reactants
Products
1 Ca atom
2 NO3- ions
2 Na atoms

37. Reactants Products 1 Ca atom 2 NO3- ions 2 Na atoms 2 OH- ions
Ca(NO3)2(aq) + 2NaOH(aq)  Ca(OH)2(s) + 2NaNO3(aq)
Reactants
Products
1 Ca atom
2 NO3- ions
2 Na atoms
2 OH- ions

38. Reactants Products 1 Ca atom 2 NO3- ions 2 Na atoms 2 OH- ions
Ca(NO3)2(aq) + 2NaOH(aq)  Ca(OH)2(s) + 2NaNO3(aq)
Reactants
Products
1 Ca atom
2 NO3- ions
2 Na atoms
2 OH- ions

39.
Homework p. 174 # 1 to 6