Chapter 10 Chemical Equations
A chemical reaction is a reaction in which at least one new substance is formed. • Example – Hydrogen and oxygen react to form water.
A chemical equation is a shorthand method of writing a chemical reaction using chemical symbols and formulas. • Example – H2 + O2 H2O
Symbols Used in Equations • (g) – gas • (cr) – crystalline solid • (l) – liquid • (aq) – aqueous solution
Law of Conservation of Mass • In an ordinary chemical reaction, mass can neither be created nor destroyed. • Mass of products must equal the mass of the reactants.
Balancing Chemical Equations • 1. Count the number of atoms of each element on both sides of the equation. • 2.Use coefficients to balance the equation. • 3. Always use the lowest possible ratio of coefficients to balance.
Practice Website • www.chem.vt.edu/RVGS/ACT/notes/scripts/bal_eq1.html
Balancing NO-NO’s • Coefficients can only be added BEFORE a chemical symbol or formula. • NEVER change a subscript to balance an equation.
Signs a Chemical Reaction Has Occurred: • Color change • Liberation of a gas • Energy change • Formation of a precipitate • Change in odor
5 Major Types of Chemical Reactions 1. Synthesis Reaction – 2 or more reactants combine to form one product. Example-
2. Decomposition Reaction – the breakdown of one reactant into its components. Example -
3. Single Replacement Reaction – one element replaces another in a compound. Example -
4. Double Replacement Reaction – the positive and negative ions of two reactants exchange places. Example-
Many times a precipitate is the result of a double replacement reaction.
5. Combustion – the burning of an organic compound in oxygen to form CO2 and H2O and energy. Example -
Practice – Classifying Reactions • Cl2 + 2KBr KCl + Br2 • 2Ag2O 4Ag + O2 • 2Na + Cl2 2NaCl • PbCl2 + Li2SO4 PbSO4 + 2LiCl
Activote Quiz CaO + H2O Ca(OH)2 This equation is an example of which type of chemical reaction: • Decomposition • Synthesis • Combustion • Single Replacement
Writing Chemical Equations 7 Diatomic elements Chlorine Fluorine Iodine Bromine Oxygen Nitrogen Hydrogen
Common Acids • Sulfuric acid • Nitric acid • Carbonic acid • Hydrochloric acid • Acetic acid • Phosphoric acid