1. Chemical Reactions and Equations
Chapter 12
Material on Midterm

2. Chemical Reactions and Equations
Essential Questions
What are some signs that a chemical reaction might have occurred?
What happens to atoms during a chemical reaction?
What happens to the total mass in a chemical reaction?
How can you recognize the type of chemical reaction by the number or type of reactants and products?
What are the different types of chemical reactions?
Why do chemical changes always involve a change in energy?
What is the difference between an endothermic and an exothermic reaction?
What factors can affect the rate of a chemical reaction?

3. Section 1: Understanding Chemical Reactions
Physical change and chemical change review (also good for midterm review)
What is the difference between the two bolded terms above?
4 signs of a chemical change (reaction) are…

4. Section 1: Understanding Chemical Reactions
Signs of Chemical Reactions
______ formation
_______ formation
The ___________________ is the solid that is produced as a result of a chemical reaction in solution
Gas
Solid
precipitate

5. Section 1: Understanding Chemical Reactions
Signs of Chemical Reactions
___________ change
Energy
Color

6. Section 1: Understanding Chemical Reactions
What really happens in a chemical reaction?
4 signs are not enough
Boiling water produces bubbles, but it’s physical
Iron turns red when it gets hot, but that’s also physical
KEY POINT: look for the ___________________ of new ______________ that have different properties
formation
products

7. Section 1: Understanding Chemical Reactions
Review: Chemical Reactions
A _______________________________ is a process in which atoms of one or more substances rearrange to form one or more new substances
Properties of starting materials (reactants) __________ from ending materials (products)
chemical reaction
differ
4 Fe O2  2 Fe2O3

8. Section 1: Understanding Chemical Reactions
How do chemical reactions form new substances?
Atoms rearrange and form new bonds
A chemical bond is the attraction between atoms when electrons are transferred, shared, or pooled
The old bonds need to ____________
The new bonds need to _________
break
form

9. Section 1: Understanding Chemical Reactions
New Bonds, New Substances
What happens with Na + Cl2?
Sodium—silver metal that reacts violently with water
Chlorine—green yellow gas that is poisonous
Na bonds and Cl-Cl bonds break
Na+ -- Cl- bonds form
Sodium chloride—harmless ionic compound that is white and dissolves in water
__________________________
NEW SUBSTANCE

10. Section 1: Understanding Chemical Reactions
Chemical Equations
“Two sodium atoms react with one chlorine molecule to produce two units of sodium chloride”
Chemical equations are summaries of reactions
Ex: ____________________________
From Reactants to Products
Reactants—_______ side of the arrow
Reactants are the ____________ substances
Products—_______ side
Products are the __________ substances
2 Na + Cl2  2 NaCl
left
starting
right
Ending

11. Self quiz
Which is/are the reactant(s)?
Which is/are the product(s)?

12. Section 1: Understanding Chemical Reactions
Tools for writing chemical equations:
You will use element symbols and subscripts to write chemical formulas
Symbol: _________ element
Coefficient: _______________ of each compound
Must _______________ to all elements (__________)
Subscript : ___________ of each atom in molecule/compound
Must __________ to element BEFORE it (multiply)
which
number
distribute
multiply
number
distribute

13. Section 1: Understanding Chemical Reactions
The Importance of Accuracy

14. Self quiz
What is each number called? Color code them

15. Self quiz
How many of each atom are there? S O S O

16. Your turn!
Go to the lab and carry out the directions there. Record your results on p 76.

17. Section 1: Understanding Chemical Reactions
Law of Conservation of mass
The law of conservation of ________ states that the total mass of the reactants before a chemical reaction is the same as the total mass of the products after the chemical reaction.
Mass is ________ lost or gained in a chemical reaction.
mass
NEVER

18. Section 1: Understanding Chemical Reactions
Relating atoms to mass in a chemical equation
When writing a chemical equation, the number of each type of element on before a reaction has to equal the number of each type of element after it.

19. Section 1: Understanding Chemical Reactions
A balanced chemical equation:
Uses_____________ to even out the numbers of elements on each side of the arrow (to conserve mass)
Has the _______ number of each atom of each element on both sides.
Ex:
2H2 + O2  2 H2O
H H
O O
coefficients
same

21. Section 1: Understanding Chemical Reactions
Try these!
___ HCl + ___ Na  ___ NaCl + ___ H2
H • H
Cl • Cl
Na • Na
___ CH4 + ___ O2  ___ CO2 + ___ H2O
C • C
O • O

22. Section 2: Types of Chemical Reactions
Synthesis Reactions
A synthesis reaction is a type of chemical reaction in which two or more substances combine and _____ one compound
General formula: ___ +_______
form
A B AB
Synthesis means TO ______
MAKE

23. Section 2: Types of Chemical Reactions
Decomposition Reactions
A decomposition reaction is a reaction where one compound _________________ and forms two or more substances
General formula: _______+___
breaks down
AB A B
Decomposing is ____________ ___________
breaking
down

24. Section 2: Types of Chemical Reactions
Single-Replacement Reactions
A single-replacement reaction is a reaction where one element ________________ another element in a compound
General formula: ____+________+____
replaces
AB C AC B
Single means ______ and replacement means to _______
ONE
SWAP

25. Section 2: Types of Chemical Reactions
Double-Replacement Reactions
A double-replacement reaction is a reaction where the negative ions in two compounds switch places, forming two new compounds
General formula: ____+________+____
AB CD AD CB
Double means TWO and replacement means SWAP

26. Section 2: Types of Chemical Reactions
Reactivity and the single-and double- displacement reaction
Elements/compounds have to be more __________ to “bump out” another element or compound
Elements in Group 1—most reactive _________
Elements in Group 17—most reactive _____________
reactive
metals
nonmetals

27. Section 2: Types of Chemical Reactions
Combustion Reactions
A combustion reaction is a chemical reaction in which a substance combines with _________ and releases energy
General formula: substance +O2  substance(s)
Products are usually carbon dioxide and water
oxygen

28. Section 2: Types of Chemical Reactions

29. Section 3: Energy Changes and Chemical Reactions
The Law of Conservation of Energy
Similar to the law of conservation of mass
The law of conservation of energy states that _________ cannot be created or destroyed
Instead, energy ____________________ Stored in chemical ________
energy
changes forms
bonds

30. Section 3: Energy Changes and Chemical Reactions
Reactions and Energy
Two main types of reactions
______________ reactions
Endothermic
Exothermic

31. Section 3: Energy Changes and Chemical Reactions
What is an endothermic reaction?
An endothermic reaction is a chemical reaction that ____________ thermal energy
Energy is usually listed as a ________________
absorbs
reactant
2 H2O +__________ 2 H2 + O2
energy
6CO2+ 6 H2O +__________ C 6H12O6 + 6 O2
energy

32. Section 3: Energy Changes and Chemical Reactions
What is an exothermic reaction?
An exothermic reaction is a chemical reaction that ______________ thermal energy
Energy is usually listed as a ___________
releases
product
2 Na Cl2  2 NaCl +____________
energy

33. Section 3: Energy Changes and Chemical Reactions
Activation Energy
________________________ is the minimum amount of energy required to start a chemical reaction
Sources of Activation Energy
Friction
Electric spark
Light
Heat
Activation energy

34. Section 3: Energy Changes and Chemical Reactions
How do I read an energy diagram?
X axis—time
Y axis—energy
Curved line—amount of energy throughout reaction
Straight line at beginning—reactants
Straight line at end—products
Curve from reactants from peak—activation energy
Difference between reactants and products— energy differ
ENDOTHERMIC: R < P (less energy in reactants)
EXOTHERMIC: R > P (more energy in reactants)

36. Section 3: Energy Changes and Chemical Reactions
Factors Affecting Rates of Reactions
________________
________________ and ______________
_______________
__________________
Surface Area
Temperature
Concentration Pressure
Catalysts
Inhibitors

37. Section 3: Energy Changes and Chemical Reactions
Surface Area
Surface area is the amount of exposed, outer surface area of a substance
_______________ the surface area of solid reactants ______________ the rate of a reaction
More reactants exposed
More collisions
Increasing
increases

38. Section 3: Energy Changes and Chemical Reactions
Temperature
A __________ temperature causes a __________ rate of reaction
Particles move faster
More collisions
More energy
More have activation energy to react
higher
faster

39. Section 3: Energy Changes and Chemical Reactions
Concentration and pressure
A ________ concentration of reactants causes a _________ rate of reaction
More particles present
Smaller distance to travel
More collisions
A __________ pressure pushes particles closer together and causes a _________ rate of reaction
higher
faster
higher
faster

40. Section 3: Energy Changes and Chemical Reactions
Catalysts
A catalyst is a substance that ___________ reaction rate by _________ the activation energy of a reaction
Is _______ changed or used up in the reaction
Allows a reaction to happen more quickly
You have thousands of them in your body
____________ are catalysts that speed up chemical reactions in living cells
increases
lowering
NOT
Enzymes

41. Section 3: Energy Changes and Chemical Reactions
Inhibitors
An inhibitor is a substance that ________________, or even stops, a chemical reaction
A greater amount of inhibitor will ________________ a chemical reaction
slows down
slows down

42. Section 3: Energy Changes and Chemical Reactions
Factor
Speeds up Reaction
Slows down Reaction
Surface Area
 Surface area
Temperature
 Temperature
Concentration
 Reactant concentration
Pressure
 Pressure
Catalysts
Catalyst present
Inhibitors
No inhibitors present