Chemical Reactions

Reactions & Equations

Chemical reactions are represented by balanced chemical equations

Essential Questions

• What is the evidence of chemical change?
• How are chemical reactions represented?
• Why do chemical equations need to be balanced?
• How do you balance chemical equations?

Chemical Reaction:
The process by which the atoms of one or more substances are rearranged to form different substances

Evidence of Chemical Reactions

• Temperature change
• Color change
• Precipitate - solid formed from two liquids
• Gas formation - may or may not have an odor
• Reversal - very difficult for chemical reactions

Reactants:
the starting substances in a chemical reaction

Products:
the substances formed during a chemical reaction

Reaction

Types of Equations

• Word Equations
• Skeleton Equations
• Chemical Equations

Balancing Chemical Equations

• Write skeleton equation
• List atoms of reactants
• List atoms of products
• Change coefficients to balance reactants and products
• Write coefficients in lowest possible ratio

Law of conservation of mass:
matter is neither created nor destroyed

Classifying Chemical Reactions

Essential Questions

• How are chemical reactions classified?
• What are the characteristics of different reactions?

Types of Reactions

• Synthesis
• Combustion
• Decomposition
• Single Replacement
• Double Replacemnt

Synthesis:
a chemical reaction in which two or more substances react to produce a single product

Combustion Reaction:
oxygen combines with a substance and releases energy as heat and light

Decomposition Reactions:
a single compound breaks down into two or more elements

Single-replacement Reaction:
atoms of one element replace the atoms of another element
in a compound

Single-Replacement

• metal replaces hydrogen
• metal replaces another metal

A metal can replace another metal listed below it on the activity series.

Double-replacement Reaction:
exchange of ions between two compounds

Anions switch places in a double-replacement reaction.

Double-Replacement products

• water
• precipitate
• gas

Writing Double-Replacement reactions

• write skeleton equation
• identify cations and anions
• switch the anions in the compounds
• write the formulas for the products
• balance the equation

Reactions in Aqueous Solutions

Essential Questions

• What are aqueous solutions?
• How are complete ionic equations written?
• How are net ionic equations written?
• How can you predict whether a reation will 
• produce a precipitate, water, or gas?

Double-replacement reactions occur between substances in aqueous solutions and produce precipitates, water, or gases.

Aqueous solution contains one or more solutes dissolved in water.

Solvent is the most plentiful substance in the solution.

Water is always the solvent in aqueous solutions.
There are many possible solvents.

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