Chemical ReactionsChemical Reactions

Reactions change one or more substances into new substances.

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Octane + Oxygen Gas Carbon Dioxide + Water

C8H18 + O2 CO2 + H2O

Written only using chemical formulas…

Chemical EquationsChemical Equations

Reactants are the substances at the beginning of the reaction.

Products are the substances at the end of the reaction.

Reactants Products

Chemical EquationsChemical Equations

The arrow () means “produces” or “yields”.

Reactions must follow the law of conservation of mass.

Chemical EquationsChemical Equations

The LCM says that matter is not created or destroyed in a reaction, but always stays the same.

Example: Formation of WaterH2 + O2 H2O

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H2 + O2 H2O

Chemical EquationsChemical Equations

H2 + O2 H2O

Coefficients can be placed before chemicals to multiply

the number of atoms!

2

H2 + O2 2 H2O

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Chemical EquationsChemical Equations

H2 + O2 2 H2O2

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2 H2 + O2 2 H2O

OK!

Chemical EquationsChemical Equations

H2 + O2 H2OStarted With:

“Balanced”: 2H2 + O2 2H2O

What About… H2 + O2 H2O2

This is a completely

different reaction so it is incorrect!

Chemical Equations

Example: H2 + N2 NH3

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H2 + N2 NH3

H2 + N2 2 NH3

3 H2 + N2 2 NH3

OK!

Chemical Equation Symbols

Cu(s) + 2 HCl(l) 2 CuCl(aq) + H2(g)

Phases of matter can be listed after the chemicals…(aq) means aqueous!

Other symbols on pg. 740