1. Theme: Changes and Reactions
Chemical Reactions
Theme: Changes and Reactions

2. Physical Properties (Review)
color
melting point
boiling point
electrical conductivity
specific heat
density
state (solid, liquid, or gas)
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3. Physical Change (Review)
Changes in physical properties
melting
boiling
condensation
No change occurs in the identity of the substance
Example:
Ice , rain, and steam are all water
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4. LecturePLUS Timberlake
Chemical Change
Atoms in the reactants are rearranged to form one or more different substances
Old bonds are broken; new bonds form
Examples:
Fe and O2 form rust (Fe2O3)
Ag and S form tarnish (Ag2S)
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5. LecturePLUS Timberlake
Learning Check 1
Classify each of the following as a
1) physical change or 2) chemical change
A. ____ a burning candle
B. ____ melting ice
C. ____ toasting a marshmallow
D. ____ cutting a pizza
E. ____ polishing silver
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6. LecturePLUS Timberlake
Solution 1
Classify each of the following as a
1) physical change or 2) chemical change
A. __2__ a burning candle
B. __1_ melting ice
C. __2__ toasting a marshmallow
D. __1__ cutting a pizza
E. __2__ polishing silver
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7. Main Ideas
Chemical Reactions are represented by Chemical Equations.

8. Main Ideas
Chemical Equations are balanced to show the same number of atoms of each element on each side.
The Law of Conservation of Matter (Mass) says that atoms won’t be created or destroyed in a chemical reaction. That is why chemical equations must be balanced!

9. Chemical Reactions are Everywhere
Respiration
Cooking

10. Chemical Reactions are Everywhere
Hair Dye
Auto Fuel

11. Vocab Reactants Products Chemical Formula Chemical Equation
Coefficients

12. LecturePLUS Timberlake
Chemical Reaction
A process in which at least one new substance is produced as a result of chemical change.
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13. Chemical Equations
Reactants produce Products
Reactants Products

14. LecturePLUS Timberlake
A Chemical Reaction
Reactants Products
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15. LecturePLUS Timberlake
Learning Check 2
A. How does an equation indicate a change in
the identity of the reacting substances?
B. How did the yellow and green reactants
combine?
C. Did all the reactants form product? Why or
why not?
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16. LecturePLUS Timberlake
Solution 2
A. How does an equation indicate a change in
the identity of the reacting substances?
The formulas of the reactants are different
than the formulas of the products.
B. How did the yellow and green reactants
combine? 1 yellow combined with 1 green.
C. Did all the reactants form product? Why or
why not? No. There were more yellow
reactants than green.
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17. How do you know when a chemical reaction takes place?
Color Change
Precipitate Formation

18. Gas Formation
Odor

19. Temperature Change
Change in Acidity

20. Representing Chemical Reactions
Chemists observe chemical reactions and have come up with a way to represent or model what is happening.
Making NaCl
Solid Sodium combines with Chlorine gas to make solid Sodium Chloride:
2Na (s) + Cl2 (g)  2NaCl

21. Chemical Equations are different from Numerical Equations
Numerical Equation: 3x + 2y = 47
Chemical Equation 2Na + Cl2  2NaCl
Reactant A + Reactant B  Product
The reactants are used up in forming the product
The arrow  shows the direction of the reaction

22. Components of a Chemical Equation
Formulas
Chemical
Formula 
2H2 + O2
2H2O
Subscript
Coefficient
Coefficient
Subscripts
(Yield)
(Reactants)
(Products)

23. Writing a Chemical Equation
Chemical symbols give a “before-and-after” picture of a chemical reaction
Reactants Products
MgO C CO Mg
magnesium oxide to produce carbon monoxide
reacts with carbon and magnesium
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24. Law of Conservation of Matter (Mass)
Matter cannot be created or destroyed. However, it can change form.
The mass of the reactants must equal the mass of the products in a chemical reaction.

25. Balancing Chemical Equations
In other words,
The total number of each type of atom must be the same on both sides of the equation.

26. Understanding Chemical Formulas
Subscripts
BaF2 the 2 in this formula is called the subscript. It refers only to the element preceding it. In this case the F (fluorine).

27. Understanding Chemical Formulas
Parentheses
Al(NO3)3 in some chemical formulas it is necessary to use parentheses. The subscript outside the parentheses refers to all the elements inside the parentheses. In this example there are: one Al (aluminum), three N (nitrogen), and nine O (oxygen).

28. Understanding Chemical Formulas
Coefficients
3 BaF2 the 3 in this formula is called the coefficient. It refers to each element that follows. In this case there would be 3 Ba (barium) and 3 F2 (a total of 6 fluorine).

29. Reaction Rates Increasing Temperature increases reaction rate
Surface Area – increasing the surface area increases the rate of reaction.
Concentration – amount of reactants in a given volume.
Stirring increases reaction rate

30. Reaction Rates - Catalysts
Catalyst – speeds up a reaction but does not change during the reaction
Catalysts do not get used up in a reaction
HCl
CH3COCH3 + I CH3COCH2I + HI
HCl is a catalyst, necessary for the reaction but not used up in the reaction, that is why it is written above the reaction arrow.

31. Reaction Rates
Increasing reactants increases the rate of reaction and increases the products made
Reactions will occur until at least one of the reactants is all used up
Mass of all the reactants is equal to the mass of all the products

32. Reaction Rates - Spectrophotometer
Spectrophotometer measures absorbance or transmission of light
Can be used to measure the disappearance or appearance of products or reactants in a chemical reaction