1. Aim # 8: How do we write and balance a chemical equation?
H.W. # 8
Study pp , pp
Ans. ques. p. 209 # 15,16
p. 210 # 19,27,31,32,
33a,d; 35d; 36a,b

2. Consider the following reaction:
lead(II)nitrate + potassium iodide → lead(II)iodide + potassium nitrate
Does this expression, in words, convey the
fact that mass has been conserved in this
chemical reaction?
Pb(NO3)2(aq) + 2KI(aq) → PbI2(s) + 2KNO3(aq)
The last equation indicates to us not only that
matter (mass) has been conserved, but the
physical phases of that matter as well.

3. I A chemical equation represents the qualitative and quantitative changes in bonding and energy that take place in a chemical reaction e.g. 2H2 + O2 → 2H2O + heat
The above reaction is exothermic.
Where would the energy term appear in an
endothermic reaction?
e.g. 2CO + energy → 2C + O2

4. II A balanced chemical equation is one in which the number of atoms of each element as products is equal to the number of its atoms as reactants.
2Na + H2O → 2NaOH + H2
atoms Na: 2 → 2
atoms H: 2 → 2 + 2
atoms O: 1 → 2
THIS EQUATION IS NOT BALANCED!

5. III Writing and balancing equations
1. Determine the reactants and products,
and write a word equation for the reaction.
e.g. Magnesium burns in oxygen to form magnesium oxide.
For the above reaction, what are the reactants and what
are the products?
magnesium + oxygen → magnesium oxide

6. 2. Write the correct formulas for all reactants and products.
Mg + O2 → MgO
Note: Oxygen is a diatomic molecule.
3. Balance the equation by supplying coefficients that will make the number of atoms of each element the same on both sides of the arrow.
2Mg + O2 → 2MgO (balanced)
Begin by examining the first element on the left side and comparing it to itself on the right side. Do the same for each element.

7. __C3H8 + __O2 → __CO2 + __H2O
4. TIP: When one of the reactants or products is an element, balance its coefficient last.
__NH3 + __O2 → __NO + __H2O
5. After balancing an equation, make sure that the coefficients are the smallest whole numbers possible.

8. Balance the following equations:
HgO → Hg O2
KClO3 → KCl O2
S O2 → SO3
Na H2O → NaOH H2

9. Write and balance equations for the following chemical reactions:
5. Zinc added to lead(II)nitrate produces zinc
nitrate and lead.
6. Sodium phosphate plus calcium chloride
yields calcium phosphate and sodium
chloride.

10. 7. Hydrogen reacts with nitrogen monoxide to produce water and nitrogen gas.