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Review from yesterday’s lesson We are learning how to balance equations because the conservation...
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Transcript of Review from yesterday’s lesson We are learning how to balance equations because the conservation...
Review from yesterday’s lessonReview from yesterday’s lesson
We are learning how to balance equations We are learning how to balance equations because the conservation of mass says because the conservation of mass says that the mass before a reaction must be that the mass before a reaction must be the same as the mass after a reaction. the same as the mass after a reaction. Atoms cannot be created nor destroyedAtoms cannot be created nor destroyed
HH22 + O + O22 ---> H ---> H22OO
Review from yesterday’s lessonReview from yesterday’s lesson We must know how to count the number of We must know how to count the number of
atoms in a substance before we can balanceatoms in a substance before we can balance
6Na6Na22OO33 Coefficient = 6Coefficient = 6 Subscript Na= 2Subscript Na= 2 Subscript O= 3Subscript O= 3
Total number of Na= 6 X 2= 12Total number of Na= 6 X 2= 12
Total number of O= 6 X 3= 18Total number of O= 6 X 3= 18
Is the blue number a coefficient or Is the blue number a coefficient or a subscript?a subscript?
NaNa22COCO3344KK22POPO44 6H6H220033LiLi
2H2H33POPO44
2Mg(OH)2Mg(OH)22
66LiClLiCl44
Count the number of atomsCount the number of atoms
5H5H22COCO33
How many H atoms?How many H atoms?
5 X 2= 10 5 X 2= 10
How many C atoms?How many C atoms?
5 X 1= 55 X 1= 5
How many O atomsHow many O atoms
5 x 3= 155 x 3= 15
Click here to go to balancing equations steps
Why do you need to balance Why do you need to balance equations?equations?
Let’s read page 80-81Let’s read page 80-81 The Law of Conservation of Mass The Law of Conservation of Mass
says that the mass of the reactants says that the mass of the reactants must equal the mass of the products.must equal the mass of the products.
In this example: In this example: HH22 + O + O22 ---> H ---> H22OO
There are 2 hydrogen’s on the left There are 2 hydrogen’s on the left and 2 Oxygen’s, but there is only 1 and 2 Oxygen’s, but there is only 1 oxygen on the right.oxygen on the right.
HH22 + O + O22 ---> H ---> H22OO
The reactants do not equal the products!The reactants do not equal the products! Where did the extra oxygen go?Where did the extra oxygen go? Atoms can’t be created nor destroyed. Atoms can’t be created nor destroyed. They didn’t go anywhere, you just need to They didn’t go anywhere, you just need to
add numbers so the sides become equaladd numbers so the sides become equal An equation is balanced by changing An equation is balanced by changing
coefficients in a somewhat trial-and-error coefficients in a somewhat trial-and-error fashionfashion
Important Vocabulary- CoefficientImportant Vocabulary- Coefficient
Coefficient- Large number located in Coefficient- Large number located in front of an element or compound in a front of an element or compound in a chemical formula. 2H= 2 hydrogen'schemical formula. 2H= 2 hydrogen's
4H4H2200Coefficient is 4Coefficient is 4HH22O O HH22O O HH22O O HH22OO
Important Vocabulary- SubscriptImportant Vocabulary- Subscript
Subscript- The small number that is Subscript- The small number that is in the lower right corner of an in the lower right corner of an elementelement
HH2200 Subscript is 2Subscript is 2 2 hydroden’s 2 hydroden’s HH H H
If there is no coefficient or subscript- If there is no coefficient or subscript- assume it is 1assume it is 1
C SC S22
Coefficient=1Coefficient=1C’s subscript= 1C’s subscript= 1S’s subscript= 2S’s subscript= 2
11
Math ReviewMath Review
Distributive Property- The coefficient times Distributive Property- The coefficient times the subscript gives the total number of the subscript gives the total number of atoms.atoms.
4H4H2200
H= 4 X 2= 8 Hydrogen’sH= 4 X 2= 8 Hydrogen’s
O= 4 X 1= 4 Oxygen’sO= 4 X 1= 4 Oxygen’s
1
3KOH3KOH
How many K atoms do I have?How many K atoms do I have?Coefficient 3Coefficient 3Subscript 1Subscript 13 X1= 33 X1= 3
How many O atoms do I have?How many O atoms do I have?Coefficient 3Coefficient 3Subscript 1Subscript 13 X 1= 33 X 1= 3
How many H atoms do I have?How many H atoms do I have?Coefficient 3Coefficient 3Subscript 1Subscript 13 X 1= 33 X 1= 3
3K3K22OO
How many K atoms do I have?How many K atoms do I have?Coefficient 3Coefficient 3Subscript 2Subscript 23 X 2= 63 X 2= 6
How many O atoms do I have?How many O atoms do I have?Coefficient 3Coefficient 3Subscript 1Subscript 13 X 1= 33 X 1= 3
2H2H22OO
How many H atoms do I have?How many H atoms do I have?Coefficient= 2Coefficient= 2Subscript= 2Subscript= 22 X 2= 42 X 2= 4
How many O atoms do I have?How many O atoms do I have?Coefficient= 2Coefficient= 2Subscript= 1Subscript= 12 X 1= 22 X 1= 2
KK33POPO44
How many K atoms do I have?How many K atoms do I have? Coefficient= 1Coefficient= 1 Subscript= 3Subscript= 3 1 X 3= 31 X 3= 3
How many P atoms do I have?How many P atoms do I have? Coefficient= 1Coefficient= 1 Subscript= 1Subscript= 1 1 X 1= 11 X 1= 1
How many O atoms do I have?How many O atoms do I have? Coefficient= 1Coefficient= 1 Subscript= 4Subscript= 4 1 X 4= 41 X 4= 4
MgMg33(PO(PO44))22
How many Mg atoms do I have?How many Mg atoms do I have? Coefficient= 1Coefficient= 1 Subscript= 3Subscript= 3 1 X 3= 31 X 3= 3
How many P atoms do I have?How many P atoms do I have? Coefficient= 1Coefficient= 1 Subscript=1 X 2= 2Subscript=1 X 2= 2 1 X 2= 21 X 2= 2
How many O atoms do I have?How many O atoms do I have? Coefficient= 1Coefficient= 1 Subscript= 4 X 2=8Subscript= 4 X 2=8 1 X 8= 81 X 8= 8
Steps for balancing equationsSteps for balancing equations
1. Draw boxes around all the 1. Draw boxes around all the chemical formulas.chemical formulas.
Never, ever, change anything inside the Never, ever, change anything inside the boxes. Ever. Really. If you do, you're boxes. Ever. Really. If you do, you're guaranteedguaranteed to get the answer wrong. to get the answer wrong.
H2 + O2 ---> H2O
Steps for balancing equationsSteps for balancing equations
2. Make an element inventory.2. Make an element inventory. How are you going to know if the equation is How are you going to know if the equation is
balanced if you don't actually make a list of balanced if you don't actually make a list of how many of each atom you have? You how many of each atom you have? You won't. You have to make an inventory of won't. You have to make an inventory of how many atoms of each element you have, how many atoms of each element you have, and then you have to keep it current and then you have to keep it current throughout the whole problem.throughout the whole problem.
See example on next slideSee example on next slide
HH22 + O + O22 ---> H ---> H22OO
ReactantsReactants ProductsProducts
Hydrogen Hydrogen (H)(H)
22 22
Oxygen (O)Oxygen (O) 22 11
But what if you have more than one formula But what if you have more than one formula on each side of the equation? Let’s practice on each side of the equation? Let’s practice
with the REACTANTS!with the REACTANTS! NaOH + HNaOH + H22COCO33 NaNa22COCO33 + H + H22OO
How many Na atoms do I have?
1 X 1 =1
How many O atoms do I have?
1 X 1= 1 1 X 3=3 1 + 3 = 4
How many H atoms do I have?
1 X 1= 1 1 X 2= 2 1 + 2= 3
How many C atoms do I have?
1 X 1= 1
Steps for balancing equationsSteps for balancing equations
3. Write numbers in front of 3. Write numbers in front of each of the boxes until the each of the boxes until the inventory for each element is the inventory for each element is the same both before and after the same both before and after the reaction.reaction.
Whenever you change a number, make sure Whenever you change a number, make sure to update the inventory - otherwise, you run to update the inventory - otherwise, you run the risk of balancing it incorrectly. When all the risk of balancing it incorrectly. When all the numbers in the inventory balance, then the numbers in the inventory balance, then the equation can balance, the equation can balance,
HH22 + O + O22 ---> H---> H22OO
ReactantsReactants ProductsProducts
Hydrogen Hydrogen (H)(H)
22 22
Oxygen Oxygen (O)(O)
22 1 1
2
4
2
4
2
Notice- I put the coefficient in front of the box- NOT inside!
Steps for balancing equationsSteps for balancing equations
4. Find the elements which 4. Find the elements which appear in the fewest numbers of appear in the fewest numbers of molecules and balance these molecules and balance these first.first.
Continue in sequence until you balance the Continue in sequence until you balance the element which appears in the most element which appears in the most molecules last.molecules last.
Tip: Start by balancing an element Tip: Start by balancing an element that appears in only that appears in only oneone reactant reactant and product.and product.
HH
OO
HH22 + O + O22 H H22OO
2
2
2
1
2
2
4
2
4
Step 1: Write formula and draw boxes
Step 2: Make an element inventory
Step 3: Add coefficients to make the inventory balance. Don’t forget to change the inventory as you go!
R P
RulesRules You cannot change a subscript.You cannot change a subscript. You cannot place a coefficient in the middle of a You cannot place a coefficient in the middle of a
formula. Hformula. H22 + O + O22 ---> H ---> H222O2O Make sure that your final set of coefficients are Make sure that your final set of coefficients are
all whole numbers with no common factors other all whole numbers with no common factors other than one. than one.
For example, this equation is balanced:For example, this equation is balanced:
4 H4 H22 + 2 O + 2 O22 ---> 4 H ---> 4 H22OO However, all the coefficients have the common However, all the coefficients have the common
factor of two. Divide through to eliminate factor of two. Divide through to eliminate common factors like this.common factors like this.
If you run into problems trying to If you run into problems trying to figure out the answer…figure out the answer…
Sometimes, you will need to find the lowest Sometimes, you will need to find the lowest common multiple in order to make an common multiple in order to make an inventory balance!inventory balance!
HH 22 22
OO 22 77
R P The lowest common multiple between 2 and 7 is 14
14 14
If you run into problems trying to If you run into problems trying to figure out the answer…figure out the answer…
What happens when the only way you can What happens when the only way you can get a problem to work out is to make one get a problem to work out is to make one of the numbers a decimal or fraction? of the numbers a decimal or fraction?
When this happens, find the largest When this happens, find the largest molecule in the equation and stick a "molecule in the equation and stick a "22" in " in front of it. front of it.
Then start the problem over. Then start the problem over. Will this work all the time? Well, no. But it Will this work all the time? Well, no. But it
will work sometimes, and give you a new will work sometimes, and give you a new strategy for hard problems.strategy for hard problems.
CC
SS
C + SC + S88 CS CS22
1
8
1
2
4
8
4
4
4
Step 1: Write formula and draw boxes
Step 2: Make an element inventory
Step 3: Add coefficients to make the inventory balance. Don’t forget to change the inventory as you go!
R P
How do I get the S’s in the products to equal 8?
NaNa
OO
Na + ONa + O22 Na Na22OO
1
2
2
1
2
2
4
4
4
Step 1: Write formula and draw boxes
Step 2: Make an element inventory
Step 3: Add coefficients to make the inventory balance. Don’t forget to change the inventory as you go!
R P
NN
OO
NN22 + O + O22 N N22OO55
2
2
2
5
2
10
4
2
4
Step 1: Write formula and draw boxes
Step 2: Make an element inventory
Step 3: Add coefficients to make the inventory balance. Don’t forget to change the inventory as you go!
R P
5
10
HINT: Find the lowest common multiple of the Oxygen molecules
NaNa
OO
Na + ONa + O22 Na Na22OO22
1
2
2
2
2
2
Step 1: Write formula and draw boxes
Step 2: Make an element inventory
Step 3: Add coefficients to make the inventory balance. Don’t forget to change the inventory as you go!
R P
How do I get the Na’s in the reactants to equal 2?
K + BK + B22OO33 K K22OO + B+ B26
Step 1: Write formula and draw boxes
Step 2: Make an element inventory
Step 3: Add coefficients to make the inventory balance. Don’t forget to change the inventory as you go!
3
ReactantsReactants ProductsProducts
KK
BB
OO
1
2
3
2
1
1
26
3
6
HINT: Start on the products side- and start with the element with the lowest number of molecules
NN
HH
NN22 + H + H22 NH NH33
2
2
1
3
2
6
2
3
6
Step 1: Write formula and draw boxes
Step 2: Make an element inventory
Step 3: Add coefficients to make the inventory balance. Don’t forget to change the inventory as you go!
R P
CsCs
NN
Cs + NCs + N22 Cs Cs33NN
1
2
3
1
2
2
6
6
6
Step 1: Write formula and draw boxes
Step 2: Make an element inventory
Step 3: Add coefficients to make the inventory balance. Don’t forget to change the inventory as you go!
R P
`Li + AlClLi + AlCl33 LiCl + Al LiCl + Al33
Step 1: Write formula and draw boxes
Step 2: Make an element inventory
Step 3: Add coefficients to make the inventory balance. Don’t forget to change the inventory as you go!
3
3
3RR PP
LiLiAlAl
ClCl
1
1
3
1
1
1
NaOH + HNaOH + H22COCO33 Na Na22COCO33 + H + H22OO22
Step 1: Write formula and draw boxes
Step 2: Make an element inventory
Step 3: Add coefficients to make the inventory balance. Don’t forget to change the inventory as you go!
2
54 4
5
Hint: We are going to start with the Na on the reactant side because it is not balanced and has the lowest number of molecules
RR PP
NaNa
OO
HH
CC
1
4
3
1
2
4
2
1
CC22HH6 6 + O + O22 CO CO22 + H + H22OO62
Step 1: Write formula and draw boxes
Step 2: Make an element inventory
Step 3: Add coefficients to make the inventory balance. Don’t forget to change the inventory as you go!
12
8
412
4
4
14
7
14
RR PP
CCHH
OO
2
6
2
1
2
3
Hint: We are going to look for the common factor of H’s
HH33POPO4 4 + KOH K + KOH K33POPO44 + H + H22OO33
Step 1: Write formula and draw boxes
Step 2: Make an element inventory
Step 3: Add coefficients to make the inventory balance. Don’t forget to change the inventory as you go!
6
7
3
6
7
RR PP
HH
PP
OO
KK
4
1
5
1
2
1
5
3
Hint: We are going to look for the lowest number of molecules that are not balanced.
Na + NaNONa + NaNO3 3 Na Na22O + NO + N2262
Step 1: Write formula and draw boxes
Step 2: Make an element inventory
Step 3: Add coefficients to make the inventory balance. Don’t forget to change the inventory as you go!
10
12
6
3
2
6
12
RR PP
NaNaNN
OO
2
1
3
2
2
1
Hint: We are going to look for the next common factor of 1 and 3