Types of Chemical Reactions. .ppt

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1. Introduction to Chemical
Reactions

2. What is a Chemical Reaction?
It is a chemical change in which one or more
substances are destroyed and one or more
new substances are created.
BEFORE
H
2 gas
and
O
2
gas
AFTER
H
2O
liquid

3. Parts of a Chemical Reaction
Reactants  Products
Reactants: Substances that are destroyed by the
chemical change (bonds breakbreak).
Products: Substances created by the chemical change
(new bonds formform).
The arrow () is read as “yields”.

4. Symbols in chemical reactions
•(s) = solid
•(l) = liquid
•(g) = gas
•(aq) = aqueous solution (the substance is
dissolved in H
2O)
•“+” separates two or more reactants or
products
•“” yield sign separates reactants from
products

5. Symbols in chemical reactions
• - it means heat is supplied to the reaction
•
⇌
- reversible reaction, this means that the
products can be changed back into the
original reactants.
•H₂0 – this is an example of a chemical formula
representing the chemical composition of the
substance.
•H₂0 – subscript, it tells how many atoms the
element has in the compound.

6. Evidence for a Chemical Reaction
1) Evolution of light or heat.

7. Evidence for a Chemical Reaction
2) Temperature change (increase or decrease)
to the surroundings.

8. Evidence for a Chemical Reaction
3) Formation of a gas (bubbling or an odor)
other than boiling.

9. Evidence for a Chemical Reaction
4) Color change (due to the formation of a new
substance).

10. Evidence for a Chemical Reaction
5) Formation of a precipitate (a new solid forms)
from the reaction of two aqueous solutions.

11. Word Equations
•Statements that indicate the reactants and
products in a chemical reaction.
•Ex. Iron (s) + chlorine (g)  iron (III) chloride (s)
•This is read as:
“Solid iron and chlorine gas react (combine) to produce solid
iron (III) chloride”

12. Translating Word Equations to
Skeleton Equations
•A skeleton equation uses chemical formulas rather
than words to identify the reactants and products of
a chemical reaction.
•The word equation
Iron (s) + chlorine (g)  iron (III) chloride (s)
•The skeleton equation
Fe(s) + Cl
2
(g)  FeCl
3
(s)
A skeleton equation is not yet “balanced” by coefficients!

13. Conservation of Mass
During a chemical reaction, atoms are neither
created nor destroyed (Conservation of Mass).
Hydrogen and oxygen gas react to form water:
H
2
(g) + O
2 (g)  H
2O
(l)

14. Conservation of Mass
H
2
(g) + O
2 (g)  H
2O
(l)
What is wrong with this equation above? Doesn’t it
appear that one oxygen atom “went missing”?
According to conservation of mass, the proper way to
write this reaction is:
2H
2
(g) + 1O
2 (g)  2H
2O
(l)
The red coefficients represent the # of molecules (or
the # of moles) of each reactant or product.

15. Not All Properties are Conserved
During Chemical Reactions!
CONSERVED NOT CONSERVED
Mass
Types of atoms
Number of each atom
Color
Physical state (solid,
liquid, gas)
Volume
Number of moles of
reactants/products

16. TYPES OF CHEMICAL REACTIONS

17. Types of Chemical Reactions
*Synthesis – The get together
*Decomposition- The break up
*Single Replacement- The Cheater
*Double Replacement- The Swap
*Combustion
**The Red names are “helpful hints”

20. Reactants – beginning substance Products- Ending Substance

21. Coefficient- number placed in front of a chemical formula in an equation.

22. SYNTHESIS REACTION
Types of synthesis:
a)Element A + Element B Compound
Na(s) + Cl
2 (g)  2NaCl(s)
a)Element + Compound A  Compound B
O
2(g) + 2SO
2(g)  2SO
3(g)
a)Compound A + Compound B  Compound C
CaO(s) + H
2
O(l)  Ca(OH)
2
(s)

27. DECOMPOSITION REACTIONS (Cont’d)
Decomposition of a compound produces two or
more elements and/or compounds
The products are always simpler than the
reactant.
Gases are often produced (H
2
, N
2
, O
2
, CO
2
, etc.)
in the decomposition of covalent compounds.
Ionic compounds may be decomposed into pure
elements by using electricity (electrolysis). This is
how pure metals are obtained from salts.

32. Single Replacement Reactions
Single replacement reactions have the general
form, A + BC  AC + B.
Question: Do all single replacement reactions
actually occur?
Answer: Not necessarily…

33. Single Replacement Reactions
How do we know which reactions will occur and
which ones will not?
We look at the “activity series”.
Elements with higher activities replace elements
with lower activities during a single-
replacement reaction, but not vice-versa.

34. HIGHEST ACTIVITY
Li
Rb
K
Ba
Ca
Na
Mg
Al
Mn
Zn
Cr
Fe
Ni
Sn
Pb
H
Cu
Hg
Ag
Pt
Au
LOWEST ACTIVITY
Activity Series for Metals

35. Activity Series for Nonmetals
Highest Activity
F
Cl
Br
I
Lowest Activity

40. Double Replacement Reactions
The general form of a double replacement reaction is:
AB + CD  AD + CB
Just like single replacement reactions, not all double
replacement reactions actually occur.
We can experimentally attempt a D.R. reaction. The reaction
occurs if:
1)A solid precipitate is produced, or
2)A gas is produced, or
3)Water is produced.
If none of the above are produced and both products are (aq),
then there is no reaction (NR)!

41. Examples of Double Replacement
Reactions:
Pb(NO
3)
2 (aq) + 2NaI (aq)  PbI
2 (s) + 2NaNO
3 (aq)
(precipitate forming)
HCl (aq) + NaOH (aq)  NaCl (aq) + H
2
O (l)
(water-forming, acid-base, neutralization)
CaCO
3
(s) + 2HCl (aq)  CaCl
2
(aq) + H
2
CO
3
(gas-forming)

H(OH)
H
2
O (l) + CO
2
(g)

43. This compound must be a hydrocarbon- made of Hydrogen and
Carbon.

44. H
2
0 and CO
2
will always be a product

45. CH
4
+ 2 O
2
→ CO
2
+ 2 H
2
O
***All Combustion must have a
hydrocarbon and 0
2
as
reactants

46. COMBUSTION REACTIONS
a)All involve oxygen (O
2
) as a reactant,
combining with another substance
b)All combustion reactions are are
exothermic
c)Complete combustion of a hydrocarbon
always produces CO
2 and H
2O
d)Incomplete combustion of a
hydrocarbon will produce CO and
possibly C

(black carbon soot) as well
Ex: CH
4
+ 2O
2
=> CO
2
+ 2H
2
O (complete combustion – blue flame)
Ex: CH
4
+ 1.5O
2
=> CO + 2H
2
O (incomplete combustion – yellow flame)
Ex: CH
4
+ O
2
=> C + 2H
2
O (incomplete combustion – yellow flame, soot)

47. Let’s React!
•Synthesis- what will be on the produce side?
•2Na + Cl
2
→ 2 NaCl (formation of table salt)
•Decomposition- what 2 elements/compounds
are products?
•2 H
2O
2 → 2 H
2O + O
2

48. •Single Replacement/displacement
•Zn + 2 HCl → ZnCl
2 + H
2
•Double Replacement/Displacement
•HCl + NaOH → NaCl + H
2O

49. •Combustion
•2 CH
2 + O
2 → 2 C0
2 2H
2O

50. How to make a reaction occur…
•Activation Energy: minimum amount of energy needed to start a chemical reaction
Rates of Chemical Reactions
•Surface Area – The more surface area that is exposed, the faster the reaction will
occur- Example- chewing your food breaks it into smaller pieces with more surface
area. It takes less time to digest your food.
•Temperature- The higher the temperature
the faster the particles move. This means
they interact more often and have more
Energy. Example: Storing Milk in the fridge slows down reactions to stay fresher
longer.

51. More ways to control a reaction
•Concentration- the amount of substance in a given volume.
Increasing the concentration allows for more particles to
react.
•Catalyst- material that increases the rate of
reaction by lowering the activation energy
•Enzymes- Cells in your body that acts as catalysts.
•Inhibitor- material used to decrease the rate of a reaction

52. Every Chemical Reaction
displays a change in Energy!!!!!
http://www.youtube.com/watch?v=tE4668aarck