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Balancing equations:. 1 st …review what we already know. A formula is a representation of a molecule of an element or a molecule of a compound. The subscript represents the number of atoms of a particular element in the molecule. 12 atoms of carbon 22 atoms of hydrogen 11 atoms of oxygen.

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Balancing equations
Balancing equations:

1st …review what we already know.


Balancing equations

A formula is a representation of a molecule of an element or a molecule of a compound.


Balancing equations

The subscriptrepresents the number of atoms of a particular element in the molecule.

12 atoms of carbon

22 atoms of hydrogen

11 atoms of oxygen


Balancing equations

If no subscript is shown. An understood one is indicated.

1 molecule of sulfuric acid

2 atoms of hydrogen

1 atom of sulfur

4 atoms of oxygen


Balancing equations

A coefficient is a number in front of a formula and represents the number of molecules.

If no coefficient is shown, one molecule is indicated.

2 molecules of sucrose

24 atoms of carbon

44 atoms of hydrogen

22 atoms of oxygen


Balancing equations

An equation is a sentence showing what is happening in a chemical reaction.


Balancing equations

The reactantsare the substances (elements or compounds) that will react. They are on the left or starting side.


Balancing equations

The products on the right side of the equation are what are formed or are produced during the reaction.


Balancing equations

  • Chemical reactions do not create or destroy atoms,

    but only rearrange them

  • Law of Conservation of Mass

    • During a chemical reaction matter is neither created nor destroyed

    • There must be as many atoms of each type on the left side of the equation as on the right side

  • Proper coefficients are placed in

    front of formulas to balance atoms

  • Subscripts cannot be changed

    • S8 + 8O2 8SO2

http://www.nisd.net/secww/science/science-taks/quiz23/mass%20quiz.htm

5 questions about conservation of mass. Allow pop-ups to view answers.


Balancing chemical reactions
Balancing Chemical Reactions

N2 + O2 ---> N2O

1

1

1

1

1x2

1x2

1x2

1x1

2 2

2 1

These don’t match. So….


Balancing chemical reactions1
Balancing Chemical Reactions

N2 + O2 ---> N2O

2

1

1

2

1

1

1x2

2x2

1x2

1x2

2x2

1x1

2x1

4

4

2 1

2

Number of reactants equals number of products.


Balancing equations

N2 + O2 ---> N2O 2, 1 ---> 2

N

N

O

N

N

N

N

O

O

N

O

N

2 diatomic nitrogens

and 1 diatomic oxygen become nitrous oxide or “laughing gas”.


Balancing chemical reactions2

To fix the Al

To fix the Cl

To fix the H

Balancing Chemical Reactions

6 2

2

3

1

1

1

1

Al 1 1

2 2

6 6

6 6

H 1 2

Cl 1 3


Which coefficients are needed to balance this equation

To finish fixing the K and try out the CrO4

1

1

1

2

1

1

1

1

1

1

1

To fix both the

NO3 and the K

Which coefficients are needed to balance this equation?



Balancing equations

3

1

3

1

1

1

1

1

1

1

1

To fix our Cl

To fix our Ag

Which coefficients are needed to balance this equation?


Balancing equations

To fix the Cl

3

1

1

1

1

Now we have 3 H’s and 2 H’s

Which coefficients are needed to balance this equation?


Balancing equations

To fix the H

To fix the Cl

6

2

3

2

1

1

1

1

To fix the Al

Which coefficients are needed to balance this equation?


Balancing equations

To fix the Ca

Finishes up the balanced equation.

3

1

1

1

1

1

3

2

1

1

1

1

1

To fix the SO4

To fix the Al and the OH

Products: 3Ca, 3S, 12O, 2Al, 6O, 6H

Check: Reactants

3Ca, 6O, 6H, 2Al, 3S and 12O

Which coefficients are needed to balance this equation?


Balancing equations

Which one is already balanced correctly?

The Al don’t match.

The H don’t match.

1

1

1x3 for S and

4x3 for O


Which one is already balanced correctly
Which one is already balanced correctly?

Cl don’t match.

Al don’t match.

Cl don’t match.


Balancing equations

http://www.creative-chemistry.org.uk/gcse/revision/equations/02.htmhttp://www.creative-chemistry.org.uk/gcse/revision/equations/02.htm

This hyperlink has you balance equations.

Instantly find out if you are correct or not.


Balancing equations

As + NaOH → http://www.creative-chemistry.org.uk/gcse/revision/equations/02.htm

Na3AsO3 + H2

6

2

3

2

2

2

3

6

2

2

1


Balancing equations

4http://www.creative-chemistry.org.uk/gcse/revision/equations/02.htm

1

2

1

3

2

3

4

4

1

1

4

3

6

2

?

3

2

2

1

2


Balancing equations

2http://www.creative-chemistry.org.uk/gcse/revision/equations/02.htm

When the above equation is balanced, the

coefficient for magnesium chloride is —

A 0

B 1

C 2

D 4

’04 Su #25


Balancing equations

2http://www.creative-chemistry.org.uk/gcse/revision/equations/02.htm

2

1

1 1 1

1 lead 1 lead

2 oxygens ≠ 3 oxygens

What are the coefficients that will balance this chemical equation?

A 2, 1, 1

B 3, 4, 2

C 2, 2, 1

D 4, 3, 2

Put a 2 here to make an even number of oxygens.

1 lead 2 lead

2 oxygens ≠ 4 oxygens

2 lead 2 lead

4 oxygens = 4 oxygens

’03 10 #45


Balancing equations

2http://www.creative-chemistry.org.uk/gcse/revision/equations/02.htm

2

2

1 1 1 1 1

Then we’ll need to put

coffecients on this side

of the arrow to finish

balancing it out.

To make the hydrogens ‘even’,

We put the coefficient 2 here.

And have a sum of 4 hydrogens,

2 potassiums and 2 oxygens

What is the coefficient for H2O when the equation is balanced?

A 1

B 2

C 3

D 4

’03 11 #19


Balancing equations

To produce http://www.creative-chemistry.org.uk/gcse/revision/equations/02.htm4 molecules of sugar, a plant needs —

F 6 molecules of hydrogen

G 12 molecules of ATP

H 18 molecules of water

J 24 molecules of carbon dioxide

Multiply the whole reaction by 4.

4( )

1

’03 10#10

4 x 6 carbon dioxide


Balancing equations

Which chemical equation supports the law of conservation of mass?

F 2H2O(l) H2(g) + O2(g)

G Zn(s) + HCl(aq) ZnCl2(aq) + H2(g)

H Al4C3(s) + H2O(l) CH4(g) + Al(OH)3(s)

J CH4(g) + 2O2(g) CO2(g) + 2H2O(g)

4 hydrogens ≠ 2 hydrogens

2 oxygens 2 oxygens

1 zinc 1 zinc

1 hydrogens ≠ 2 hydrogens

1 chlorine 2 chlorines

4 aluminums 1 aluminum

3 carbons 1 carbon

2 hydrogens ≠ 3 hydrogens

1 oxygen 3 oxygens

1 carbons 1 carbon

4 hydrogens = 4 hydrogens

4 oxygens 4 oxygens

’04 11 #32


Balancing equations

The energy not stored in the bonds of the carbon dioxide and water must have left in the form of heat.

+ = +

Reactants = Products

Why is the sum of the products’ energy in this reaction less than the sum of the reactants’ energy?

A Energy is given off as heat.

B The products absorb available energy.

C Energy is trapped in the reactants.

D The reactants’ energy is less than the melting point of glucose.

’04 11 #37


Balancing equations

According to the law of conservation of mass, how much zinc was present in the zinc carbonate?

A 40 g

B 88 g

C 104 g

D 256 g

64 + 192 = 152 + ?

64 + 192 – 152 = ?

’03 11 #39


Balancing equations

If all the reactants in a chemical reaction are was present in the zinc carbonate?

completely used, which of the following

statements accurately describes the

relationship between the reactants and the

products?

F The products must have a different

physical state than the reactants.

G The total mass of the reactants must

equal the total mass of the products.

H The reactants must contain more complex

molecules than the products do.

J The density of the reactants must equal

the density of the products.

Reactants become Products

2H2 + O2  2H2O

20 grams + 10grams = 30 grams

’04 Su #40


Balancing equations

100 g was present in the zinc carbonate?

Reactants → Products

The chemical equation shows CaCO3 being heated. Which of these statements best describes the mass of the products if 100 g of CaCO3 is heated?

A The difference in the products’ masses is equal to the mass of the CaCO3.

B The sum of the products’ masses is less than the mass of the CaCO3.

C The mass of each product is equal to the mass of the CaCO3.

D The sum of the products’ masses equals the mass of the CaCO3.

’04 11 #29


Balancing equations

When 127 g of copper reacts with 32 g of oxygen gas to form copper (II) oxide, no copper or oxygen is left over. How much copper (II) oxide is produced?

F 32 g

G 95 g

H 127 g

J 159 g

127 + 32 = ?

’04 11 #40


Balancing equations

After copper (II) oxide, no copper or oxygen is left over. How much copper (II) oxide is produced?

The illustrations show a conservation-of-mass

experiment. The solution in the beaker lost mass because —

F materials have less mass at high temperatures

G the mass of the reactants and products was less than 100 g

H sodium sulfate (Na2SO4) is lighter than air

J some of the water molecules turned into gas

Before

Some of the water

evaporated because of the heat.

After( less

than 100 g)

Before(100 g)

’0410#30

REACTANTS →Products The sum of the reactants = the sum of the products.


Balancing equations

According to this information, what is the chemical formula for aluminum sulfate?

A AlSO4

B Al2(SO4)3

C Al3(SO4)2

D Al6SO4

’04 11 #23


Balancing equations

+1 +2 +3 +4 -3 -2 -1 0


Balancing equations

+1 +2 +3 +4 -3 -2 -1 0

Na P

Li C


Balancing equations

+1 +2 +3 +4 -3 -2 -1 0

Na+1 P-3

Li C


Balancing equations

+1 +2 +3 +4 -3 -2 -1 0

Na+1 P-3

3 1

Li C


Balancing equations

+1 +2 +3 +4 -3 -2 -1 0

Na+1 P-3

3 1

Li C


Balancing equations

+1 +2 +3 +4 -3 -2 -1 0

Na+1 P-3

3 1

Li C


Balancing equations

+1 +2 +3 +4 -3 -2 -1 0

Balanced!

Na3P

Li C


Balancing equations

+1 +2 +3 +4 -3 -2 -1 0

Na3P

Li+1C±4


Balancing equations

+1 +2 +3 +4 -3 -2 -1 0

Na3P

Li+1C±4

4 1


Balancing equations

+1 +2 +3 +4 -3 -2 -1 0

Na3P

Li+1C±4

4 1


Balancing equations

+1 +2 +3 +4 -3 -2 -1 0

Na3P

Li4C

Balanced!


Balancing equations

According to this information, what is the chemical formula for aluminum sulfate?

A AlSO4

B Al2(SO4)3

C Al3(SO4)2

D Al6SO4

’04 11 #23


Balancing equations

The chemical formula for calcium chloride is — for aluminum sulfate?

F Ca2Cl

G CaCl

H CaCl2

J Ca2Cl3

’04 11 #38