Unit 3: Chemical Reactions Add the new notes to your table of contents, and then turn to the next clean page and set up your title and date

Tape the two slides into your INB flat down, directly under your title - they do not need to flip up

Identifying A Substance (Recap) As you learned in Unit 2: Substances react chemically in characteristic ways, which can be used to identify a substance For example – Baking Soda always reacts with vinegar by fizzing/bubbling Properties that can be used to identify a substance are unique or characteristic Examples: density, chemical reactions, chemical formula During a chemical change, the atoms that make up the original substance are regrouped into different molecules This is what forms the new substances The change in formation of atoms means the new substances have new physical and chemical properties

Notice in these two examples that many properties have changed, but as we noted in Unit 2, the only ones that prove a chemical change has occurred are the unique characteristic properties of: Chemical formula Melting point/Boiling point Density

Conservation of Mass Also notice that before and after the chemical change occurs, we have the same number of atoms for each element

Conservation of Mass Also notice that before and after the chemical change occurs, we have the same number of atoms for each element Before the change we have 2 Copper atoms and 2 Oxygen atoms, after we still have 2 Copper atoms and 2 Oxygen atoms, although they have been regrouped/rearranged Before the change we have 2 Hydrogen atoms and 1 Oxygen atom, after we still have 2 Hydrogen atoms and 1 Oxygen atom, although they have been regrouped/rearranged

Add Conservation of Mass to your Index The Law of Conservation of Mass states that matter cannot be created or destroyed – the mass before and after a chemical reaction has occurred will always be the same The total number of each type of atom in a chemical process is conserved, and thus the mass does not change. Matter is conserved because atoms are conserved in physical and chemical processes. Add Conservation of Mass to your Index

Is Mass Conserved here?

Is Mass Conserved here?

Endothermic and Exothermic Reactions Some chemical reactions release energy, while others store energy. A chemical reaction involves the breaking of bonds in the reactants and the forming of bonds in the products. It takes energy to break bonds. Energy is released when bonds are formed.

Endothermic Reactions Exothermic Reactions two substances react and the temperature of the mixture decreases In an endothermic reaction, it takes more energy to break the bonds of the reactants than is released when the bonds of the products are formed two substances react and the temperature of the mixture increases In an exothermic reaction, more energy is released when the bonds of the products are formed than it takes to break the bonds of the reactants

Endothermic Reactions Exothermic Reactions Add Endothermic Reaction and Exothermic Reaction to your Index