Transcript Chemical Formulae, Types of Reactions, Chemical Equations

Chemical Formulae,
Types of Reactions,
Chemical Equations,
and Balancing
Chemical Formulae
• Indicates the # of atoms of each type in a
molecule or the ratio of the # of atoms of
each type in a compound
• Worksheet to practice writing chemical
formulae
Types of Chemical Reactions
• Chemical reactions are chemical changes
in which new substances are formed.
Synthesis Reaction
• 2 or more simple substances combine to
form a more complex substance
• These reactions come in the general form
of:
A + B ---> AB
Eg. Synthesis Reaction
• Hydrogen gas combined with oxygen gas
can produce a more complex substance
 water!
• The chemical equation for this synthesis
reaction looks like:
2H2 + O2  2H2O
Reactant + reactant  product
Decomposition Reaction
• A more complex substance breaks down
into its more simple parts. One reactant
yields 2 or more products.
• These reactions come in the general form:
AB ---> A + B
Eg. Decomposition Reaction
• Water can be broken down into hydrogen
gas and oxygen gas. The chemical
equation for this decomposition reaction
looks like:
2H2O  2H2 + O2
reactant
 product + product
Single Replacement Reaction
• A single uncombined element replaces
another in a compound. Two reactants
yield two products.
• These reactions come in the general form
of: A + BC ---> AC + B
Eg. Single Replacement Reaction
• Zinc combines with hydrochloric acid, the
zinc replaces hydrogen. The chemical
equation for this single replacement
reaction looks like:
Zn + 2HCl  ZnCl2 + H2
reactant + reactant  product + product
Double Replacement Reaction
• Parts of two compounds switch places to
form two new compounds. Two reactants
yield two products.
• These reactions are in the general form:
AB + CD ---> AD + CB
Eg. Double Replacement Reaction
• Silver nitrate combines with sodium
chloride, two new compounds - silver
chloride and sodium nitrate are formed
because the sodium and silver switched
places. The chemical equation for this
double replacement reaction looks like:
AgNO3 + NaCl  AgCl + NaNO3
reactant
+ reactant  product + product
Combustion
• Oxygen combines with another compound
to form water and carbon dioxide.
• Eg. CH4(g) + 2O2(g)  2H2O(g) + CO2(g)
Acid - Base
• Acid and base react with each other. The
H+ ion in the acid reacts with the OH- ion
in the base, causing the formation of
water.
• The product of this reaction is salt and
water: HA + BOH ---> H2O + BA
Eg. Acid - Base
• Reaction of hydrochloric acid and sodium
hydroxide to form sodium chloride and
water
HCl + NaOH ---> NaCl + H2O
• Questions to review 6 types of reactions
• Possibly get students to work in groups to
learn types of reactions
– Matching questions = definition of each
reaction, match up to an example
Chemical Equations
• A way of writing the changes in a chemical
reaction
• Reactants combine and produce new
chemical substances – products
–
Reactants  Products
• The # and type of atoms in the reactants
should always be equal to the # and type
of atoms in the products
Chemical Equations Cont’d
H2(g) + O2(g)  H2O(l)
2
2
2 1
• Symbols in brackets = state
– s = solid
– l = liquid
– g = gas
– aq = aqueous
2H2(g) + O2(g)  2H2O(l)
4
2
4 2
Balancing Chemical Equations!
• Balanced chemical equations tells you the
ratio in which the elements are combined
and produced
• A chemical equation is balanced when the
number of atoms of each type on each
side of the equation is the same.
How to Balance an Equation
1.
Start with word equation and name reactants and
products
Eg. methane gas + oxygen gas  carbon dioxide + water
2.
Replace the words with formulae and rewrite equation
Eg. CH4 + O2  CO2 + H2O
3.
Count # atoms of each element
Element
C
H
O
4.
Reactants
1
4
2
If # atoms on both sides are not equal, need to
balance the equation
Eg. CH4 + 2O2  CO2 + 2H2O
5.
Products
1
2
3
Add physical state symbols
Eg. CH4(g) + 2O2(g)  CO2(g) + 2H2O(l)
• Worksheet with balancing equation
questions