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Section 2.6—Chemical Reactions. If we’re going to do chemical reactions with antacids, we’d better know how to write them!. Diatomic Molecules. This is not in the notes so you should pay attention, and add it in!!!!!!. - PowerPoint PPT Presentation
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Section 2.6—Chemical Reactions
If we’re going to do chemical reactions with antacids, we’d better know how to write them!
Diatomic Molecules
This is not in the notes so you should pay attention, and add it in!!!!!!
Some elements are so chemically reactive that, when they are not bonded to any other elements, they find another atom of their same kind to bond with.
Diatomic Molecules
To write a formula for a diatomic molecule you write the symbol of the element and use a two as a subscript.
Which elements form diatomic molecules?
Well, I am glad you asked!
Diatomic Molecules
There are seven diatomic molecules:
Element MoleculeHydrogen H2
Nitrogen N2
Oxygen O2
Fluorine F2Chlorine Cl2Bromine Br2Iodine I2
Diatomic Molecules
There are two good ways to remember the diatomic molecules
First – Remember a funny word!
HOFBrINCl
Diatomic Molecules
Second – Remember a funny phrase:
The six that make a seven plus hydrogen.
Now back to our regularly scheduled notes.
Watch as 2 H2 and 1 O2 undergo a chemical reaction
OO OO
Bonds and atoms are rearranged to form new compounds.
HH
HH HH HH
2 H2 + O2 2 H2O
Chemical Reactions
OO OO
Bonds and atoms are rearranged to form new compounds.
HH HH
OOHH
HHOOHH
HH HH HHThe compounds in the end are different from those in the beginning
Bonds are broken and formed between different atoms
2 H2 + O2 2 H2O
Chemical Reactions
Chemical Equations
The “sentence” of chemistry that shows how the starting materials and the final products of a chemical reaction
Examples of Chemical Equations
H Cl
HMg H
H Cl
Mg ClCl
H Cl
HMg H
H Cl
Mg ClCl
Word equation: magnesium metal is reacted with aqueous hydrochloric acid to produce aqueous
magnesium chloride and hydrogen gas
Visualization
Formula equation: Mg (s) + 2 HCl (aq) MgCl2 (aq) + H2 (g)
Parts of a Chemical Equation
NaCl (aq) + AgNO3 (aq) AgCl(s) + NaNO3 (aq)
Reactants
States of matter Arrow
Products
The starting materials for the reaction—each compound is separated by a “+”
s = solidl = liquidg = gasaq = aqueous (dissolved in water)
Read as:YieldsProducesFormsMakesetc.
Formed in the reaction
You must write each chemical formula correctly first! (Section 2.2)
“and”, “is mixed with” or “reacts with” = +“yield”, “produces” and “forms” =
Writing Chemical Equations
We will learn to balance equations in the next section, so don’t worry about it now!
Let’s Practice #1
Example:Write the word equation into symbol form
Aluminum metal is reacted with hydrochloric acid to form aluminum chloride and hydrogen gas
Aluminum metal is reacted with hydrochloric acid to form aluminum chloride and hydrogen gas
Let’s Practice #1
Al + HCl AlCl3 + H2
Example:Write the word equation into symbol form
Let’s Practice #2
Example:Write the word equation into symbol form
Copper (II) nitrate and sodium hydroxide form copper (II) hydroxide and sodium nitrate
Copper (II) nitrate and sodium hydroxide form copper (II) hydroxide and sodium nitrate
Let’s Practice #2
Cu(NO3)2 + NaOH Cu(OH)2 + NaNO3
Example:Write the word equation into symbol form
NaCl + AgNO3 AgCl + NaNO3
Double Replacement Reactions
The cations from two compounds replace each other.
ClCl
NaNa
AgAg
OO OO
NN
OO
ClCl
AgAg
NaNa
OO OO
NN
OO
Two ionic compounds switch ions
Double Replacement Reactions
A X B Z A XBZAA XX BB ZZ AA XXBBZZ
General format of a double replacement reaction:
Combine the cation of the first reactant with the anion of the second reactant
CaCl2 + AgNO3
1
Products of a Double Replacement
Combine the cation of the second reactant with the anion of the first reactant
CaCl2 + AgNO3
2
Products of a Double Replacement
& balance charges with subscripts when writing formulasRemember to write cations first …
AgCl
CaCl2 + AgNO3
3
Ca(NO3)2 +CaCl2 AgNO3+
Products of a Double Replacement
Only leave subscripts that are in the original compound there if they are a part of a polyatomic ion!
Neutralization Reactions
General format of a neutralization reaction:
X B XBH HO HO
HXX BB XXBBH HOO HO
HH
OOH
Neutralization reactions are double replacement reactions where one cation is “H” and one anion is “OH” and water is formed
Combine the cation of the first reactant with the anion of the second reactant
H2 SO4 + NaOH
1
Products of a Neutralization Reaction
Combine the cation of the second reactant with the anion of the first reactant
H2 SO4 + NaOH
2
Products of a Neutralization Reaction
& balance charges with subscripts when writing formulasRemember to write cations first …
HOH
H2 SO4 + NaOH
3
Na2SO4 +H2 SO4 NaOH+
Products of a Neutralization Reaction
Only leave subscripts that are in the original compound there if they are a part of a polyatomic ion!
You can write the water as “HOH” when you combine the cation & anion or you can change it to “H2O”
Let’s Practice #3
Example:Write the
products for this reaction
Sr(OH)2 + HBr
Let’s Practice #3
SrBr2 + HOH
Example:Write the
products for this reaction
Sr(OH)2 + HBr
Let’s Practice #4
Example:Write the
products for this reaction
HCl + Ca(OH)2
Let’s Practice #4
CaCl2 + HOH
Example:Write the
products for this reaction
HCl + Ca(OH)2
