1. CHAPTER 7 Chemical Reactions: An Introduction
as expected, you will use this stuff ‘til the day you leave the class!

2. 7.1 Evidence for a Chemical Reaction
matter can combine or break apart to produce new kinds of matter w/ different properties
= chemical reaction
how can you recognize one??? look for clues!

3. Bubbles form (gas formation) – Alka-Seltzer in water, baking powder/soda in dough; some metals in acid
all give off gas = evidence of chm rxn!
dogs barking!!
more gas!!

4. Color changes leaves, peeled apple, burned toast; all evidence of chemical rxn cool video demo!!

5. Appearance of a new substance (e.g. soap scum)

6. Changes in heat and light – lit candle, burning charcoal, fuel oil on fire;
all give off heat/light = chm rxn
may take in heat or light (e.g. photosynthesis, baking soda in water)
cool demo!!
Another cool demo!!

7. 7.2 Chemical Equations
hydrocarbons are a group of cmpds which release E in chm rxns; e.g.…
propane + oxygen  carbon dioxide + water + energy reactants products
above is too long, so...
C3H8 + O2  CO2 + H2O + energy
this is a chemical equation

9. Reversible rxns!
rarely is a rxn one way; often both ways; e.g.
H2 + O2  H2O + energy but also…
H2O + energy  H2 + O2 so…
H2 + O2  H2O + energy

10. What is it now!?
What is it now?
law of conservation of mass = in a chemical rxn atoms are neither created nor destroyed
discovered by Antoine Laurent Lavoisier w/ experiments in a closed system

11. all atoms are all accounted for in typical chm rxn
better way of stating it:
all atoms are all accounted for in typical chm rxn
correct chm eq will obey LawConsMass! e.g. C + O2  CO2

12. gotta make reactant and product masses equal lookie here…
H2 + O2  H2O
what is wrong?
all O’s not accounted for! how to fix? play w/ coefficients!
2H2 + O2  2H2O

13. coefficients (the numbers in front) will show the proportion of the diff cmpds, e.g.:
2H2 + O2  2H2O
2 hydrogens : 1 oxygen (or)
2 zillion hydrogens : 1 zillion oxygens (or)
2 mol hydrogen : 1 mol oxygen

15. 7.3 Balancing Chemical Reactions
when balancing, you may not mess w/ cmpd identities (formulae)!!! play only w/ coefficients!
make sure you have right chm formula first,
THEN balance using coefficients!
when counting, multiply atoms in cmpd by coeff
coefficients are whole numbers – make sure you use whole numbers!! make sure it is the simplest ratio!! so there!
Check this out!

17. examples C2H4 burns in oxygen to form carbon dioxide and water
C2H4 + O2  CO2 + H2O
C2H4 + 3O2  2CO2 + 2H2O
sodium and water react to form sodium hydroxide and hydrogen gas
Na + H2O  NaOH + H2
2Na + 2H2O  2NaOH + H2

18. examples magnesium nitride is formed from its elements
first, what is magnesium nitride?
Mg3N2
Mg + N2  Mg3N2
3Mg + N2  Mg3N2

19. examples
nitrogen monoxide gas reacts with hydrogen gas to form nitrogen gas and water
NO + H2  N2 + H2O
2NO + 2H2  N2 + 2H2O

20. examples
lithium metal reacts with chlorine gas to form solid lithium chloride
Li + Cl2  LiCl
2Li + Cl2  2LiCl

21. examples diboron trioxide reacts with water to form boric acid, B(OH)3
B2O3 + H2O  B(OH)3
B2O3 + 3H2O  2B(OH)3

22. examples
solid iron(III) oxide reacts with aqueous nitric acid to form aqueous iron(III) nitrate and water
Fe2O3 + HNO3  Fe(NO3)3 + H2O
Fe2O3 + 6HNO3  2Fe(NO3)3 + 3H2O

23. examples
solid ammonium nitrite is heated to produce nitrogen gas and water vapor
NH4NO2  N2 + H2O
NH4NO2  N2 + 2H2O