1. Unit Four
Chemical Reactions

2. Chemical Reactions
Process by which the atoms of one or more substances are rearranged to form different substances

3. 5 Types of Chemical Reactions
Synthesis
Combustion
Decomposition
Double-Replacement
Single-Replacement

4. Synthesis Reactions What does synthesis mean? A + B AB
2 or more compounds or elements go together to build a more complex compound
Which example is a synthesis equation?

5. Combustion Reactions What is necessary for something to burn?
Oxygen combines with a substance and releases energy in the form of heat and light
OXYGEN IS ALWAYS A REACTANT!
Which example is a combustion equation?

6. Decomposition Reactions
What does decompose mean?
A single compound breaks down into 2 or more elements or new compounds
AB A + B
Which example is a decomposition equation?

7. Double Replacement Reactions
Exchange of ions between 2 ionic compounds
AX + BY AY + BX
Which example is a double replacement equation?

8. Single Replacement Reactions
One element replaces another element in a compound
A + BX AX + B
A metal will not always replace another metal…it depends on how active they are…most active replaces least active
Which example is a single replacement equation?

9. Summary of Reaction Types
Funny Analogies

10. What do all the small letters mean?
(s) solid
(l) liquid
(g) gas
(aq) dissolved in water

11. Terminology Word Equations: statements that describe a reaction
Skeleton Equations: uses formulas not words to describe a reaction-NOT BALANCED
True Chemical Equation: a balanced skeleton reaction that follows the law of conservation of matter

12. Writing Chemical Equations
Read a description of the reaction
Note what is reacted with what
Note what is yielded or produced
Write formulas for each compound
REMEMBER TO CRISS-CROSS IF IONIC!

13. Balancing Chemical Equations
Reflects the law of conservation of mass which says…

14. Steps to Balancing an Equation
Write the skeleton equation. BE SURE THE FORMULAS ARE WRITTEN CORRECTLY.
Inventory reactants
Inventory products
Add coefficients to make atoms of each element equal on both sides of the equation
Reduce the coefficients if possible

15. Examples

16. Write and Balance the Following
Magnesium sulfate + calcium hydroxide yields magnesium hydroxide + calcium sulfate
Iron + silver chloride yields silver + iron (III) chloride

17. So…..
In a lab with beakers and chemicals, how do I know that a reaction is happening?

18. Evidence of Chemical Reactions
Temperature change
exothermic, endothermic
Release energy in the form of light
Color change
Odor
Gas bubbles
Formation of a solid…called a precipitate.

20. Reactions in Aqueous Solution
More than 70% of earth is covered by water
66% of the human body is water
MANY chemical reactions occur in water
Often form solids called precipitates
Remember: Ionic compounds dissociate in water.

21. Net Ionic Equations
Represent reactions of ionic compounds in aqueous solution by writing complete ionic equations
Remove spectator ions (those appear on both sides of the equation but aren’t in the precipitate)
Leaves a net ionic equation that can be balanced

23. Percent Composition
The relative amounts of each element in a compound are expressed in percent composition. AKA: percent by mass of each element
% of element = grams of element X 100
grams of compound
EXAMPLES: pg. 191

24. Calculating Empirical Formula
Empirical formula: lowest whole number ratio of the atoms of the elements in a compound
Empirical formula doesn’t have to be the same as the actual molecular formula of the compound. Ex. Hydrogen peroxide

25. Calculating Empirical Formula
Given % composition.
Assume 100 grams. Allows you to change the % to g.
Convert to moles.
Find lowest number of moles.
Divide all moles by the lowest number.
Multiply by a number if necessary to get whole numbers.
Example: pg. 193

26. Calculating Molecular Formulas
Molecular Formula= n(empirical formula)
n= molecular formula mass/molar mass of empirical
Examples: pg. 194

27. (particles= atoms, formula units, or molecules)
Introducing the Mole
Avogadro’s Number:
1 mole = 6.02 x 1023 particles
(particles= atoms, formula units, or molecules)
Molar Mass: mole = ________ grams of an element or compound
(can be found on the periodic table)

28. Chemical Quantities Groups
Gather 2 sheets of paper, periodic table, calculator, notes, and long WS
Instructions:
Jar Lab: Number paper 1 to 5. Calculate the # of grams in each jar. Be sure to write the given, unknown, and conversion factor
% Composition and Empirical Formula Cards: Do 3 cards. Be sure to write down the #’s.
IF DONE: Begin writing the equations for the LONG WS

29. We cannot get rid of the mole!
Stoichiometry
We cannot get rid of the mole!

30. What is Stoichiometry?
Quantitative relationships between reactants used and products formed
RELATES ONE COMPOUND TO A DIFFERENT COMPOUND
Based on law of conservation of matter

31. What is Stoichiometry?
CANNOT DO STOICHIOMETRY WITHOUT A BALANCED EQUATION!
Why? The coefficients in a balanced equation tell us how many moles of each compound are used or produced in the reaction.

32. What is Stoichiometry?
Mole Ratio: ratio between the number of moles of any two compounds in a balanced chemical equation
COEFFICIENTS

33. Stoichiometric Calculations
2 relationships in stoichiometry:
Molar mass
Mole ratios

34. Stoichiometric Calculations
Mole to mole conversions
Mole ratio
Mole to mass conversions
Mole ratio and molar mass
Mass to mass conversions
Molar mass, mole ratio, molar mass

35. Limiting Reactants
Limiting reactant: ends the reaction because it runs out
Excess reactant: left over at the end of the reaction
AMOUNT OF PRODUCT THAT YOU GET IN A REACTION DEPENDS ON THE LIMITING REACTANT…BECAUSE IT STOPS THE REACTION!

36. Limiting Reactants Finding which is limiting: Will be given two things
Solve for unknown twice (one time using each given)
Which is the smallest answer? That is the answer to the problem.
The limiting reactant is the given found at the front of that solution!

37. Limiting Reactants
Since the limiting reactant stops the reaction, USE THE LIMITING REACTANT TO SOLVE FOR THE AMOUNTS OF PRODUCTS PRODUCED.