1. Chemical Reactions

2. Chemical Reactions
A chemical reaction is a process by which one or more substances are changed into one or more different substances.
Evidence of a chemical reaction might include:
A color change
Formation of a gas
Formation of a precipitate
Absorption or release of energy.This may include heat, sound, light and electrical energy.

3. Chemical Equations (stoichiometric) coefficients
Depict the kind of reactants and products and their relative amounts in a reaction.
4 Al(s) O2(g) ---> 2 Al2O3(s)
The numbers in the front are called
(stoichiometric) coefficients
The letters (s), (g), (aq) and (l) indicate the physical states of compounds.

4. Chemical Equations 4 Al(s) + 3 O2(g) ---> 2 Al2O3(s)
This equation means
4 Al atoms + 3 O2 molecules ---give--->
2 molecules of Al2O3 OR…
4 moles of Al + 3 moles of O give--->
2 moles of Al2O3

5. Chemical Equations
Because the same atoms are present in a reaction at the beginning and at the end, the amount of matter in a system does not change.
The Law of the Conservation of Matter

6. Chemical Reactions
In a chemical equation, reactants (the items on the left side) change into products (the items on the right side).
Rusting:
Iron + oxygen --> iron (III) oxide
This equation is a chemical sentence.

7. Chemical Reactions Symbols Used in Chemical Equations
+ Used to separate reactants or products
Yield sign: Separates reactants and products.

8. Chemical Reactions Pt
A formula above a yield sign tells you a catalyst was used - Pt in this case. A catalyst is a substance that speeds up a reaction without being used up in the reaction.
Ex. MnO2 with decomposition of H2O2.
heat
Indicates heat is supplied to reaction. Often a triangle may be used rather than the word.

9. Chemical Equations
Because of the principle of the conservation of matter,
an equation must be balanced.
It must have the same number of atoms of the same kind on both sides.
Lavoisier, 1788

10. Chemical Reactions Rules for balancing equations:
The law of conservation of mass must be followed.
In order to do this, then each side of the equation must have the same number of atoms.
We do this by adding coefficients to the reactants and products. (Always in WHOLE NUMBERS!)
___BaCl2(aq) + ___ H3PO4(aq) --> ___Ba3(PO4)2(s) + ___HCl(aq)

11. Rules for Balancing Equations
___BaCl2(aq) + ___H3PO4(aq) --> ___Ba3(PO4)2(s) + ___ HCl(aq)
Rules for Balancing Equations:
1. Be sure you have correct formulas for reactants and products.
2. If the same complex ion appears on both sides, then treat it as one group.

12. Rules for Balancing Equations
3. Check for 2 to 3 ratios – do them first!
Balance highest (noncomplex ion) #’s next
4. Save single elements for last.
5. Check all numbers once you’re done…
3BaCl2(aq) +2 H3PO4(aq) > Ba3(PO4)2(s) + 6 HCl(aq)

13. Balancing Equations
___ Al(s) + ___ Br2(liq) ---> ___ AlBr3(s)

14. Balancing Equations
3 Al(s) Br2(l) ---> 2 AlBr3(s)

15. Balancing Equations ____Ca3P2 + _____ Na ----> _____Ca + _____ Na3P
____LiOH(aq) _____ H2(g) > ___ Li (s) _____ HOH(l)

16. 1 Ca3P Na ---> 3 Ca Na3P
2 LiOH(aq) + 1 H2(g) > Li (s) + 2 HOH(l)