Chemical Reactions

Chemical Reactions Describe how elements/molecules bond with one another when they are combined.

Chemical Reactions Involve the physical breaking of chemical bonds, the rearrangement of atoms, and the formation of new bonds.

Rules For A Chemical Reaction In order to say that a chemical reaction has taken place; one of the following criteria must be met: A new solid (precipitate) is formed A new gas is formed Water was created In other words, something new must be made!

Rules For A Chemical Reaction A new solid (precipitate) is formed A new gas is formed Water was created This means that any process that changes the physical composition of a substance is NOT a chemical reaction! These processes are called physical changes No change occurred in how the atoms of the substance were bonded or arranged.

Physical Changes Can you think of some examples of physical changes?

Chemical Equations Chemical reactions are described using chemical equations. Equations show what elements/molecules are involved in the reaction (reactants) and what the result of the reaction is (products).

Chemical Equations The arrow shows the direction in which the reaction is occurring, therefore telling you which side is your reactants and which side is your products. Reactants or Reagents are typically shown on the left of the equations. Products are typically shown on the right.

Writing Chemical Equations We can use our current knowledge of valence electrons, oxidation states, and chemical formulas to write proper chemical equations! What rules must be followed when writing the formulas for your reactants & products? Metal & Non-Metal : Criss-cross your charges Non-Metal & Non-Metal: Use the prefixes in the name

Keys to Writing Chemical Equations You must be able to identify how a reaction is occuring based upon a written description. Reactants are ID’d by finding the chemicals that were: used, combined, reacted, mixed Products are ID’d as the chemicals that were: created, produced, resulted in, made, yields

Try It! Write the equation for a reaction between Iron (III) Nitrate and Sodium Hydroxide, which creates Iron (III) Hydroxide and Sodium Nitrate.

Writing Chemical Equations A solution of Iron (III) Nitrate is added to a solution of Sodium Hydroxide to produce a Iron (III) Hydroxide precipitate and aqueous Sodium Nitrate.

Complete Chemical Equations Writing proper formulas for reactants and products is only the first step in writing a complete chemical equation. Looking back at the description for the reaction of Iron (III) Nitrate and Sodium Hydroxide, what other info was given that could be included in your equation?

Phases After you have figured out the correct chemical formulas for the reactants and products, you must provide information on what phase the chemical is in during the reaction. Remember your phases? Solid (s) Liquid (l) Gas (g) Aqueous (aq)

Phases Solid (s): Firm and stable in shape; not fluid. Generally referred to as a precipitate when formed in a solution. Examples: Gas (g): An air-like, fluid substance which expands freely to fill any space available.

Phases Liquid (l): Fluid and unstable in shape. Must be a pure substance (made of only one type of molecule or element). Very Rare. Examples: Aqueous (aq): Same characteristics as a liquid (Fluid and unstable in shape), but must be dissolved in water. Very common, often described as a solution.

Phases In Chemical Equations Phases are included in parentheses after each reactant and product formula. How to figure out your phases Element: Use the periodic table (black, blue, red) Compound: Use the description (precipitate, solution, gaseous, vapor, etc.) - Later you will predict phases of ionic compounds

Complete Chemical Equations A complete chemical equation includes: Proper formulas for all reactants and products Phases for all reactants and products ??? There is a third component which you will figure out for yourself in lab!