Upload
gavin-west
View
216
Download
1
Tags:
Embed Size (px)
Citation preview
Reactions & Equations
When you take substances and rearrange their atoms to form new substances you have created a chemical reaction!
Chemical reactions are another name for chemical changes. These occur all around us
Chemical Equations
Chemical Equations are used by chemists to communicate to other chemists what is happening during a chemical reaction.
Chemical Equation Chemical equations are used to represent
chemical reactions. They show: Reactants
The starting substances Products
The new substances formed (s) (l) (g) (aq)
Tells you the state of matter or if a water solution Coefficients
Tell you the lowest whole-number ratio of amounts of substances in the equation.
Reactant 1 + Reactant 2 + etc. Product 1 + Product 2 + etc.
Plus sign separate each substance
The arrow is used to separate the reactants from the product.
Sometimes above the arrow there is information telling us what substances were used to help the chemical reaction run. These substances are called catalysts
BalancingChemical Equations
Balance the formula equation by the use of coefficients to balance the number of each type of atom on the reactant and product sides of the equation.
Balancing Tips:
1. Count the atoms of the elements in the reactants
2. Count the atoms of the elements in the products
3. Change the coefficients to make the number of atoms of each element equal on BOTH sides of the equation. (NEVER change the subscript in a chemical formula to balance an equation).
4. Make sure the coefficients are in their lowest possible ratio.
5. Check your work!
Example
Hydrogen gas reacts with oxygen gas to produce water.
H2 (g) + O2 (g) H2O (l)
2 H2 (g) + O2 (g) 2 H2O (l)
Example w/ Polyatomic Ions
Solutions of lithium phosphate and calcium chloride react to make a lithium chloride solution with solid calcium phosphate.
Li3PO4 (aq) + CaCl2 (aq) LiCl (aq) + Ca3(PO4)2 (s)
2 Li3PO4 (aq) + 3 CaCl2 (aq) 6 LiCl (aq) + Ca3(PO4)2 (s)
Example
Solid iron(III) oxide reacts with carbon monoxide gas to produce solid iron (I) oxide and carbon dioxide gas.
Fe2O3 (s) + CO (g) Fe2O (s) + CO2 (g)
Fe2O3 (s) + 2CO (g) Fe2O (s) + 2CO2 (g)
One Last Example
Iron metal reacts with chlorine gas to form a solid iron(III) chloride.
Fe(s) + Cl2(g) FeCl3(s)
2Fe (s) + 3Cl2(g) 2FeCl3 (s)
The amount of atoms of an element MUST be equal on both sides of the equation.
That is why we balance equations, to account for all the matter used in the reaction
Types of Reactions
Combination (Synthesis) reaction Decomposition reaction Single-replacement reaction Double-replacement reaction Combustion reaction Neutralization reaction
involve acids & bases
You will be able to identify the different types of reactions.
You will recognize them by their reactants & products
For some you will be able to predict whether a reaction will happen at all.
Combination Reaction
What does combination mean?
In this reaction two or more simpler compounds or elements form one product.
Also called a synthesis reaction
General Equation: A + B AB
Decomposition Reaction
What does Decomposition mean?
In this reaction: One reactant would break down into two or more simpler substances.
General Equation: AB A + B
Single-replacement Reaction
An element and a compound react together and a new element and new compound are formed
Sometimes called Displacement Reaction
General Equation: General Equation: A + BX A + BX AX + B AX + B Examples:
Na + KCl K + NaCl
F2 + 2 LiCl 2 LiF + Cl2 Watch the next two slides
More Single ReplacementReactions
Metals replace metals (and hydrogen) Examples:
2Al + 3CuSO4 Al2(SO4)3 + 3Cu
Zn + H2SO4 ZnSO4 + H2
2 Na + 2 H2O 2 NaOH + H2
We can tell whether a reaction will happen using the Activity Series of Metals
Some metals are more reactive than others
The MORE active metals replace less active metals
There is a list on page 217 – Table 8.2
You will be given this list on quizzes/tests
Single Replacement
A metal higher on the list replaces one lower on the list.
So if the element by itself is higher, the reaction happens, if element by itself is lower, it doesn’t
If there is no reaction we write NR after the arrow
Single Replacement
Note the * H can be replaced in acids
by metals higher than it on the list
Only the first 4 (Li - Na) react with water.
Activity Series Examples:
Will a reaction occur for the following?
Pb + KCl
Al + H2O
What does it mean that Ag is on the bottom of the list?
Single Replacement Continued
Nonmetals can replace other nonmetals Limited to F2 , Cl2 , Br2 , I2 (the Halogens)
The order of activity follows the periodic table. Higher replaces lower.
Will a reaction occur for the following?
F2 + KCl
I2 + LiBr
Br2 + KCl
Double-replacement Reactions
Two compounds react together to form two new compounds.
Use the charges on the ions to help in determining the new substances formed.
These are sometimes called double- displacement reactions
General Equation: General Equation: AX + BY AX + BY AY + BX AY + BX
Double Replacement
Reactants must be two ionic compounds or acids.
Usually in aqueous solution
NaOH (aq) + FeCl3 (aq) The positive ions change place.
Na+OH- + Fe3+Cl- Fe3+OH- + Na+Cl-
3 NaOH + FeCl3 Fe(OH)33 + 3 NaCl
Watch the next slide
Double ReplacementTips
The reaction one of the products will do the following:
A. doesn’t dissolve in water and forms a solid called a precipitate
B. is a gas that bubbles out.C. is a covalent compound (usually water).
Polyatomic ions don’t change from side to side
Combustion Reactions:
A hydrocarbon compound is reacted with oxygen gas
A hydrocarbon? What’s a hydrocarbon? If the combustion is complete, the products will
be CO2 and H2O.
If the combustion is incomplete, the products will be CO and H2O
or just C and H2O.
O2 will ALWAYS be the second reactant
Common Acids
Acids that you must know (memorize): HCl = hydrochloric acid HNO3 = nitric acid
H2CO3 = carbonic acid
H2SO4 = sulfuric acid
H3PO4 = phosphoric acid
Common Bases
How to know the bases: Look for hydroxide polyatomic ion (OH-) Name the base from the name of the metal
and then hydroxide. EX: NaOH potassium hydroxide Mg(OH)2
Neutralization Reactions
A reaction in which an acid and a base react in aqueous solution to produce a salt and water. A salt is an ionic compound made up of a cation
from a base and an anion from an acid. These reactions are double-replacement
reactions. General Equation:General Equation:
Acid (aq) + Base (aq) Salt (aq) + Water (l) EX: Mg(OH)2 (aq) + 2 HCl (aq) MgCl2 (aq) + 2 H2O (l)