1. Chemical Equations and Reactions
10/20/2017 7:48 AM
Chemical Equations and Reactions
Chapter 8
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2. Unit Essential Question:
What can chemical equations tell us?

3. Lesson Essential Question:
How can we describe chemical reactions?

4. Before we start…
In this chapter you MUST be able to name BOTH types of compounds- ionic and covalent.
Be sure to brush up on naming as needed!
You also MUST know which elements exist as diatomic molecules! (BrINClHOF)

5. Section 1: Describing Chemical Reactions
New substances are formed.
Reactants = starting materials.
Products = ending materials.
Recall evidence of a chemical change/reaction:
Formation of a gas (bubbles/change in odor).
Formation of a precipitate (solid).
Change in energy: heat/light/sound given off (change in temperature).
Change in color.
Chemical reactions are not always visible.
Properties of substances change during chemical reactions.
This is review from earlier this year. Chemical reaction is just another name for chemical change. Remember the “evidence” is only a clue, it does not prove a reaction took place. Only checking the properties to see if they changed can prove a reaction.

6. Equations Word Equations: use names. Chemical Equations: use formulas.
Replace “and” with +
Replace “yields”, “produces”, “forms” etc. with 
Ex: methane and oxygen form carbon dioxide and water.
methane + oxygen  carbon dioxide + water
Chemical Equations: use formulas.
Replace words with chemical formulas.
Ex: methane + oxygen  carbon dioxide + water
CH4 + O2  CO2 + H2O
We will write word equations first. The plus sign and arrow will begin our process of switching it to formulas.

7. Information in an Equation
Equations are like recipes – they give necessary information:
Ingredients (substances involved)
amounts
Can also show physical states and conditions needed:
Symbol
Meaning
(s), (l), (g)
Substance in solid, liquid, or gas form
(aq)
Substance in aqueous form (dissolved in water)
“Produces”, “yields”, etc. indicating results of reaction 
Reversible reaction in which products can reform into reactants; final result is a mixture of products and reactants
Reactants are heated; temperature is not specified
Name or chemical formula of a catalyst, added to speed up a reaction
Specific temperature or pressure needed for this reaction
We will learn reactions in Chapter 8 and then apply the amounts more in Chapter 9 with application of math. For now, we need to know the ‘extra’ info that can be helpful in a reaction. The states of matter or other reaction conditions can show us how to repeat a reaction for lab experiments. Δ
heat Pd
500 oC
2 atm

8. Practice Problems
Aqueous iron (II) chloride and lithium bromide react to form aqueous lithium chloride and iron (II) bromide. Write the word equation.
Solid calcium carbonate is heated and decomposes to form solid calcium oxide and carbon dioxide gas. Write the chemical equation. Include phases!

9. Section 1 Homework
Honors: pg. 266 #2,3,9,11,13,17(a,b)

10. Lesson Essential Question:
Why must chemical equations be balanced?
How are chemical equations balanced?

11. Section 2: Balancing Chemical Reactions
Law of Conservation of Mass!
There must be the same number of each atom on both sides.
Change coefficients NOT subscripts!
Ex:
In order to balance a reaction, you cannot change the formulas. If you do not write the correct formula, you will not have the right reaction and may have trouble getting it to balance. You must know your ions and prefixes from Chapters 5 & 6 – study!!! You can only change the coefficients – the big numbers in front to balance an equation.

12. Steps for Balancing Equations
Write formulas for all chemicals.
Count atoms.
Listing #s of each atom on both sides is helpful.
Keep polyatomic ions as a group if they appear on both sides.
Insert coefficients.
It often helps to balance H and O last.
Try odd-even technique: place an even coefficient in front of a chemical that has an odd # of atoms- makes all atom #’s even.
Verify Results.
Check #’s of atoms to make sure they’re equal!
Following these steps can make sure you end up with the correct answer. Checking your final answer is a great way to catch your mistakes.

13. Practice Problem #1
Balance the equation for the reaction of iron(III) oxide with hydrogen to form iron and water.
Write equation: Fe2O3 + H2  Fe + H2O
Count # atoms
on each side:
(3) Balance # atoms on each side.
(4) Double check your answer:
Fe2O3 + H2  Fe + H2O
Fe: Fe:
O: O:
H: H:
If an atom exists by itself
Fe: Fe:
O: O:
H: H:

14. Practice Problem #2
The reaction of ammonia with oxygen produces nitrogen monoxide and water vapor. Write a balanced equation for this reaction.
Must have even numbers in front of products because the O2 in the reactants means there can only ever be an even number of O atoms on this side. So, there must also only ever be an even number of O atoms on the products side too. Since there are odd numbers of O atoms in both products, an even number MUST go in front so as to obtain a number that is even for the total number of O atoms.

15. Practice Problem #3- Using Fractions
Sometimes it is helpful to use fractions as coefficients when balancing equations.
This can help you to arrive at the correct coefficients more quickly.
Ex: C6H14 + O2  CO2 + H2O
It is easy to first balance the C and H atoms:
C6H14 + O2  6CO2 + 7H2O
Try using a fraction to balance the O atoms:
C6H /2 O2  6CO2 + 7H2O
Now multiply all coefficients by 2 to get whole #s.
2C6H O2  6CO2 + 7H2O

16. Lesson Essential Question:
How can chemical equations be classified and how is this used to predict products?

17. Section 3: Classifying Chemical Reactions
Classifying reactions allows us to better predict products.
We will look at five types: combustion, synthesis, decomposition, single displacement, and double displacement.
More than these five types exist.
Some fall into more than 1 type.
Some don’t fall into any type.
We will start with just predicting the type of reaction given the entire equation to look at. Next we will look at predicting products if we are given reactants. If you know the type of reaction, you can predict how the reactants will change.

18. Combustion Generic formula: AB + O2  CO2 + H2O Examples:
AB is a hydrocarbon (H and C bonded together).
O may be present too.
Always form CO2 and H2O.
Examples:
CH4 + O2  CO2 + H2O
C6H6 + O2  CO2 + H2O
Normally burning something needs oxygen from the air. If the reactant contains both carbon and hydrogen, the products will always be carbon dioxide and water. If there is incomplete burning, other products are possible (CO, etc).

19. Synthesis (Addition) Generic Formula: A + B  AB
Can be element + element yielding one compound.
Al + O2  Al2O3
Can also be compound + compound yielding one compound. These products must be memorized depending on the compounds.
We will not cover these types.
Ex: water + metal oxide  metal hydroxide
H2O + CaO  Ca(OH)2
Simple synthesis (2 elements) are very easy to predict products. When 2 compounds come together, it gets more complicated. I tried to show some simple examples of these. We will learn 2 compounds can also react in other ways.

20. Decomposition Generic Formula: AB  A + B
Can be a binary compound yielding two elements.
NaCl  Na + Cl2
Can be a ternary compound (3 elements in the compound). These products must be memorized depending on the compound breaking down.
We will not cover these types.
Ex: metal chlorate  metal chloride and oxygen:
KClO3  KCl + O2
Like simple synthesis, simple decomposition (2 elements) is easy to determine. However, the ternary compounds that break down yield different products. Again I tried to give you some good examples to follow.

21. Practice
Name the type of reactions listed below and predict the product(s) for each:
Sr + O2 
C3H6 + O2 
Al(OH)3 
CO2 + H2O 
SrO
H2O + CO2
Al2O3 + H2O
H2CO3

22. Bi >Cu > Hg > Ag > Pt > Au
Single Displacement
nonmetal
metal
When A is a metal: A + BC  AC + B
If metal A is more reactive than metal B it displaces B’s spot in the compound:
Cu + AgNO3  Cu(NO3)2 + Ag
If metal B is more reactive than metal A, no reaction occurs:
Cu + HCl  no reaction (NR)
METAL REACTIVITIES
Li > Rb > K > Ba > Sr >Ca > Na > Mg > Al > Mn >
Zn > Cr > Fe > Cd > Co > Ni > Sn > Pb > H2 > Sb >
Bi >Cu > Hg > Ag > Pt > Au
First you must know if the single element is a metal or nonmetal. Then you must check to see if they can “switch” places based on reactivities. You do not have to memorize this list – it will be given on quizzes/tests.

23. Single Displacement continued
When A is a nonmetal: A + BC  BA + C
If nonmetal A is more reactive than nonmetal C it displaces C’s spot in the compound:
Cl2 + KBr  KCl + Br2
If nonmetal C is more reactive than nonmetal A, no reaction occurs:
Cl2 + KF  no reaction (NR)
NONMETAL REACTIVITIES
F2 > Cl2 > Br2 > I2
metal
nonmetal
You should know this short activity series for nonmetals- relates directly back to their valence electrons and shielding. Fluorine has the least shielding so is most able to obtain its 8th valence electron.

24. Double Displacement Generic Formula: AB + CD  AD + CB
When a compound plus a compound yields two new compounds. The metals ‘switch partners’ with the nonmetals.
H2SO4 + NaOH  H2O + Na2SO4
I think of double displacement as ‘square dancing’ since the compounds “switch partners”. Please notice the order of the ions in the products. The positive ion must remain first, so the products are always AD + CB or CB + AD. C must be before B in the formula.
We will look more at double displacement in Section 4 when we learn about net ionic equations. Generally double displacement reactions form a precipitate (solid).

25. More Practice Problems
Predict the product(s) and write a balanced equation for the reaction of potassium with chlorine.
Magnesium is added to a solution of lead (II) nitrate. Will a reaction happen? If so, write the equation and balance it.
Additional Practice: pg.279 #1-4 and pg.282 #1-3

26. Lesson Essential Question:
Why are some parts of a reaction left out?

27. Section 4: Writing Net Ionic Equations
Ionic compounds dissolve in water  ions separate and spread out.
We will be taking out ions that do not make a solid, pure liquid, or gas. These spectator ions are not important to the reaction taking place and can be ignored.

28. Section 4: Writing Net Ionic Equations
As long as a compound does not form a solid (precipitate), pure liquid, or gas, it will exist as ions in water, NOT as a compound.
Ions that do not form a solid, pure liquid, or gas are called spectator ions (remain as ions in solution).
Do not participate in the reaction.
Use solubility rules to determine if a compound will remain as a solid in water (pg. 288).
Write total ionic equation (all ions present).
Cross out all spectators that appear on BOTH sides of the equation.
Write final answer with remaining species- this is the net ionic equation.
We will be taking out ions that do not make a solid, pure liquid, or gas- basically any ion with (aq) is removed. These spectator ions are not important to the reaction taking place and can be ignored.

29. Example Potassium iodide solution + lead (II) nitrate solution ?
Double displacement:
KI (aq) + Pb(NO3)2 (aq)  ?
KI (aq) + Pb(NO3)2 (aq)  KNO3 (?) + PbI2 (?)
Use solubility rules or clues in question.
2 KI (aq) + Pb(NO3)2 (aq) 2 KNO3 (aq) + PbI2 (s)
Total Ionic:
2 K+ (aq) + 2 I - (aq) + Pb+2 (aq) + 2 NO3- (aq) 
2 K+ (aq) + 2 NO3- (aq) + PbI2 (s)
Net Ionic:
2 I - (aq) + Pb+2 (aq)  PbI2 (s)
You do not need to memorize the solubility rules on p.288 – they will be given or a clue to the precipitate will be given in the problem.
This is the reaction taking place.

30. Steps for Writing Net Ionic Equations
List what you know.
Identify the type of reaction.
Identify reactants (and products if provided).
Write a balanced chemical reaction.
Use type to predict products (if not told what they are).
Use solubility rules to predict states of matter.
Write total ionic equation.
Separate ions (anything still in solution = aq).
Do not separate any solids, liquids, or gases!
Find the net ionic equation.
Cancel out any spectator ions and write remaining species.
Double check that equation is balanced.
Over time, you may be able to skip step #3, but I recommend it as good step until you master these types of problems. Don’t forget when you separate compounds into ions that you can only separate aqueous compounds and to include the charge on the ions.

31. Practice Problem #1
Write the net ionic equation for the reaction that occurs when zinc is placed in a copper (II) sulfate solution.
1) Reaction type:
2) Balanced Equation:
3) Total Ionic Equation:
4) Net Ionic Equation: