Chemical Reactions Mrs Wolfe I II IV V

Chemical Reactions Mrs. Wolfe I II IV V

Signs of a Chemical Reaction Change in heat and light · Exothermic – GIVES OFF heat · Endothermic – ABSORBS heat n Formation of a gas n Formation of a precipitate n Color change n

Chemical Equations – Used to SYMBOLIZE a reaction A+B C+D REACTANTS PRODUCTS

Chemical Equation Yield Sign Subscripts

Chemical Equations

Describing Equations n Describing Compounds: · individual atom = “atom” · covalent substance = “molecule” · ionic substance = “unit” CO 2 Mg Mg. O molecule of carbon dioxide atom of magnesium unit of magnesium oxide

Wording an Equation 2 H 2(g) + O 2(g) 2 H 2 O(g) n Coefficients apply to the COMPOUND. n Describe this reaction… n Two molecules of hydrogen gas react with one molecule of oxygen gas to form two molecules of gaseous water. n Diatomic = covalent compound

Practice Problem: Zn(s) + 2 HCl(aq) Zn. Cl 2(aq) + H 2(g) One atom of solid zinc reacts with two units of aqueous hydrochloric to produce one unit acid of aqueous zinc (II) chloride and one molecule of hydrogen gas.

Writing Equations Two atoms of aluminum react with three units of aqueous copper(II) chloride to produce three atoms of copper and two units of aqueous aluminum chloride. 2 Al(s) + 3 Cu. Cl 2(aq) 3 Cu(s) + 2 Al. Cl 3(aq)

Law of Conservation of Mass n mass is neither created nor destroyed in a chemical reaction total mass stays the same n atoms can only rearrange n 4 H 36 g 2 O 4 g 32 g 4 H 2 O

Coefficients keep the equation in balance.

A. Balancing Steps 1. Count ATOMS on each side. 3. Add coefficients to make #s equal. Coefficient subscript = # of atoms 4. Reduce coefficients to lowest possible ratio, if necessary. 5. Double check atom balance!!!

C. Balancing Example Aluminum and copper(II) chloride react to form copper and aluminum chloride. 2 Al + 3 Cu. Cl 2 3 Cu + 2 Al. Cl 3 2 1 Al 1 2 3 1 Cu 1 3 6 2 Cl 3 6

Practice Problem Iron (III) oxide decomposes to form Iron (II) oxide and molecular oxygen gas. 2 4 Fe. O + 4 2 Fe 1 2 4 6 3 O 3 4 6 2 Fe 2 O 3 O 2