Balancing, Conservation and Reaction Types Review

Chemistry Review 1

Definition:

A chemical reaction is when a reactant changes into a product.​

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​Parts of a Chemical Equation

In the Equation, H₂ + O₂ -> H₂O...

• H₂ and O₂ are reactants

• H₂O is the product

​The chemical symbols show us the composition of a molecule.

The subscripts tell us the number of atoms in each molecule.​

Coefficients tell us the number of molecules present.

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Balancing Chemical Equations

When you balance chemical equations, you add to the coefficient to balance the number of atoms on each side of the chemical equation.

​ In 2H₂ + O₂ -> 2H₂O

• 2 is the coefficient for H₂O

  • ​this means that we have two molecules of H₂O instead of one molecule.

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Why do we balance?

Law of Conservation of Mass

This law states that atoms are never created nor destroyed in a chemical reaction. They are only rearranged.

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Multiple Choice

Based on the law of conservation of mass, balancing chemical reactions helps show how matter is _______ during a chemical reaction.

• created or destroyed

• rearranged

• changed at the atomic level

• neither created nor destroyed

Reaction Types

There are 5 different types of reactions:

• Synthesis: two or more reactants combine to form a larger molecule.

• Decomposition: a larger molecule breaks up into smaller molecules.

• Single Replacement: when one atom replaces another atom.

• Double Replacement: when two atoms in different molecules are replaced.

• Combustion​: reactants are C_xH_y and O₂ hydrocarbons. Products are CO₂ and H₂O.