Making new substances

Chemical Reactions are represented by Chemical Equations. Chemical Equations are balanced to show the same number of atoms of each element on each side. The Law of Conservation of Mass says that atoms won’t be created or destroyed in a chemical reaction. That is why you have to balance chemical equations!

Exothermic Endothermic

Cooking Respiration

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Chemists observe chemical reactions and have come up with a way to represent or model what is happening. Making NaCl Solid Sodium combines with Chlorine gas to make solid Sodium Chloride: 2Na (s) + Cl 2 (g)  2NaCl (s) : How many of the entire molecule there are. Coefficient: How many of the entire molecule there are. Example: 2H 2 O = H 2 O + H 2 O 3NaCl = NaCl + NaCl + NaCl Subscript: How many atoms of that specific element there are. Example: CaF 2 = Ca + F + F KNO 3 = K + N + O + O +O

C 12 H 22 O 11 There are 12 atoms of Carbon There are 22 atoms of Hydrogen There are 11 atoms of Oxygen If there is not a subscript listed, it is understood to be 1. Example: NaCl There is one atom of Sodium There is one atom of Chlorine

2H 2 SO 4 This means there are 2 compounds of Sulfuric Acid. Think: H 2 SO 4 + H 2 SO 4 Counting the atoms: Hydrogen – 4 Sulfur – 2 Oxygen - 8

Numerical Equation: 3x + 2y = 47 Numerical Equation: 3x + 2y = 47 Chemical Equation 2Na + Cl 2  2NaCl Chemical Equation 2Na + Cl 2  2NaCl 2H 2 + O 2  2H 2 O Reactants Products Reactant A + Reactant B  Product Reactant A + Reactant B  Product The reactants are used up in forming the product The reactants are used up in forming the product The arrow  shows the direction of the reaction The arrow  shows the direction of the reaction The  read as “yields” The  read as “yields”

SymbolPurpose +Separates more than one reactant or product  Separates reactants from products. Indicates direction of reaction (s)Identifies a solid state (aq)Identifies that something is dissolved in water (l)Identifies liquid state (g)Identifies gaseous state

In a chemical reaction, matter is neither created nor destroyed. Atoms won’t change their identity (e.g. a Carbon atom can’t become an Iron atom) This means that you have to have the same number of each type of atom on each side of the chemical equation. Conservation of Mass Video