1. Balancing Equations

2. Chemical Equations & 5 Types of Reactions

3. Chemical Equations
Representation of a chemical reaction using symbols and formulas
Example: H + OH  H2O
reactants “yields” products
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4. Chemical Equation Signs
The (+) sign is read as “and” and shows that the substances on either side of it combine
Yields () is the chemical equivalent of the equals sign, and it signifies which direction the reaction is taking place.
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5. Chemical Equations Mg + O2  MgO
Magnesium and oxygen yields magnesium oxide
Think about this: Are the numbers of atoms for each element the same on both sides of the equation?
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7. 1: Synthesis Reaction
Two or more simple substances combine to form a new more complex substance.
A + B  C
Example:
2Na + Cl2  2NaCl
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8. 2: Decomposition Reaction
A complex substance breaks down into two or more simpler substances. It’s the reverse of synthesis.
C  A + B
Example:
2H2O  2H2 + O2
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9. 3: Single-Replacement Reaction
An uncombined element replaces an element that is part of a compound.
A + BX  AX + B
Example:
2Na + 2H2O  2NaOH + H2
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10. 4: Double-Replacement Reaction
Different atoms in two different compounds replace each other.
AX + BY  AY + BX
Example:
BaBr2 + 2KCl  BaCl2 + 2KBr
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11. Hydrocarbon + Heat  CO2 + H2O
5: Combustion Reaction
This reaction always involves heat, a hydrocarbon, water, and carbon dioxide.
Hydrocarbon + Heat  CO2 + H2O
Hydrocarbon=A type of covalent compound containing carbon and hydrogen and sometimes oxygen
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13. Law of Conservation of Mass
Chemical reactions involve the rearrangement of atoms, not the creation or destruction of them
The number of atoms that go into the reaction (REACTANTS) must equal the number of atoms that come out of the reaction (PRODUCTS)
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14. Balancing Chemical Equations
Mg + O2  MgO
This equation is not balanced
In order for an equation to be balanced, the number of atoms of each element must be the same on both sides of the equation.
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15. Balancing Chemical Equations
Mg + O2  MgO
First count the number of atoms of each element on each side of the equation.
Reactants Products
Mg=1 Mg=1
O=2 O=1
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16. Balancing Chemical Equations
Next, balance the number of atoms using coefficients
Coefficients are numbers placed in front of symbols and formulas
Use coefficients because changing subscripts would mean altering the substance we already have
Coefficients just change the amount of the substances we already have
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17. Balancing Chemical Equations
Mg + O2  MgO
So if we have
Reactants Products
Mg=1 Mg=1
O=2 O=1
This means we need to change the numbers of some things so everything is equal
In other words, the number of magnesium atoms are equal, and the number of oxygen atoms are equal
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18. Balancing Chemical Equations
So use coefficients
Mg + O2  MgO
2Mg + O2  2MgO
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19. Balancing Chemical Equations
The last thing to do, check your work by counting atoms of each element.
2Mg + O2  2MgO
Reactants Products
Mg=2 Mg=2
O=2 O=2
If the numbers are equal then you’re in business
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23. Energy, Rates, and Indicators
Chemical Reactions
Energy, Rates, and Indicators

24. Energy Conservation
Energy is always involved in a chemical reaction. Reactions either give off or absorb energy in the form of heat or light.
Law of Conservation of Energy: Either way, energy is neither created nor destroyed, it just changes form.
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25. Exothermic Reactions Chemical reaction in which energy is released
Heat is released from the reactants during an exothermic reaction.
Examples: chem-lights, heat packs
The energy of the products is less than the energy of the reactants
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26. Endothermic Reaction Chemical reaction in which energy is absorbed
Energy is absorbed by the reactants during an endothermic reaction
Example: decomposition of sodium chloride (table salt) requires the absorption of electric energy
The energy of the products is more than the energy of the reactants
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27. Activation Energy
Both exothermic and endothermic reactions require something called activation energy - The amount of energy required for the chemical reaction to proceed.
The “spark” needed for the reaction called the activated complex.
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28. Catalysts Some reactions are very slow.
Substances called catalysts speed up the rate of a reaction but are not changed by the reaction.
Catalysts are thus present before and after a reaction in the same form
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29. Catalysts
Activation energy – the “energy hill” the reactants need to get over in order for the reaction to proceed.
Catalysts provide a “shorter hill”
Thus less energy is required for the reaction to occur
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30. Collision Theory
Chemical reactions occur when bonds between atoms are broken, the atoms are rearranged, and new bonds are formed
In order for this to occur, atoms must collide at precisely the correct angle with the proper amount of energy
The more collisions that occur the faster the rate of the chemical reaction
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31. Concentration and Reaction Rate
Measure of the amount of substance in a given volume
The more of a substance there is the more particles of reactants there can be for collisions
Higher concentrations of reactants mean higher reaction rates
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32. Surface Area and Reaction Rate
Which dissolves faster?
sugar cube grounded sugar
Increases in surface area means a faster reaction rate
Medicines work this way
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33. Temperature and Reaction Rate
Collision theory states that particles are constantly in motion
Well, as temperature increases, the particles speed up, thus more collisions can occur
An increase in temperature means an there is an increase in the rate of a reaction
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34. Indicators of Chemical Change
Gas evolution
Color Change
Precipitate forms
Release/Absorption of Energy
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