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

2 2 2 1 4 2 4 2

• Symbols in brackets = state– s = solid– l = liquid– g = gas– aq = aqueous

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 Equation1. Start with word equation and name reactants and

productsEg. methane gas + oxygen gas carbon dioxide + water

2. Replace the words with formulae and rewrite equationEg. CH4 + O2 CO2 + H2O

3. Count # atoms of each elementElement Reactants Products C 1 1 H 4 2 O 2 3

4. If # atoms on both sides are not equal, need to balance the equation

Eg. CH4 + 2O2 CO2 + 2H2O

5. Add physical state symbolsEg. CH4(g) + 2O2(g) CO2(g) + 2H2O(l)

• Worksheet with balancing equation questions