Balancing Equations Chapter 6

How do we know a chemical reaction has occurred? The color changes. A solid forms. Bubbles form. Heat and/or a flame is produced, or heat is absorbed.

Vocab. A chemical change involves a rearrangement of the atoms; this is called a chemical reaction. A chemical reaction is represented by a chemical equation. Reactants-to the left of the arrow Products-to the right of the arrow

Label the reactants and products in the below equations. 2Na+Cl22NaCl 2NaCl2Na + Cl2

Chemical Equations Are sentences. Describe what happens in a chemical reaction. Reactants ® Products Equations should be balanced. Have the same number of each kind of atoms on both sides because ...

Law of Conservation of Mass In a chemical reaction, atoms are neither created or destroyed. The atoms on the left (reactants) must equal (balance) the atoms on the right (products).

Balancing equations CH4 + O2 ® CO2 + H2O 1 C 1 4 H 2 2 O 3 Reactants Products 1 C 1 4 H 2 2 O 3

Balancing equations CH4 + O2 ® CO2 + 2 H2O 1 C 1 4 H 2 4 2 O 3 Reactants Products 1 C 1 4 H 2 4 2 O 3

Balancing equations CH4 + O2 ® CO2 + 2 H2O 1 C 1 4 H 2 4 4 2 O 3 Reactants Products 1 C 1 4 H 2 4 4 2 O 3

Balancing equations CH4 + 2O2 ® CO2 + 2 H2O 1 C 1 4 H 2 4 4 4 2 O 3 Reactants Products 1 C 1 4 H 2 4 4 4 2 O 3

Physical States Physical states are represented by abbreviations beside the symbols of a chemical equation. s solid l liquid g gas aq dissolved in water (aqueous)

Abbreviations (s) ¯ (g) ­ (aq) heat D catalyst

Meaning A balanced equation can be used to describe a reaction in molecules and atoms. Not grams. Chemical reactions happen molecules at a time or dozens of molecules at a time or moles of molecules.

What is wrong with this equation? Al2S3 + Cl2 AlCl3 + S

Balancing Equations __Al2S3 + __Cl2 __AlCl3 + __S In order to balance the equation, we have to write numbers in front. Try to balance the previous example by writing numbers in front (coefficients) of each element or compound. __Al2S3 + __Cl2 __AlCl3 + __S

Answer 1_Al2S3 +_3_Cl2_2_AlCl3 + _3_S

Practice balancing these Ca(OH)2 + H3PO4 ® H2O + Ca3(PO4)2 Cr + S8 ® Cr2S3 KClO3(s) ® KCl(g) + O2(g) Solid iron(III) sulfide reacts with gaseous hydrogen chloride to form solid iron(III) chloride and hydrogen sulfide gas. Fe2O3(s) + Al(s) ® Fe(s) + Al2O3(s)

Practice balancing these 3Ca(OH)2+2H3PO4 ®6H2O + 1Ca3(PO4)2 16Cr + 3S8 ® 8Cr2S3 2KClO3(s) ® 2KCl(g) + 3O2(g) Solid iron(III) sulfide reacts with gaseous hydrogen chloride to form solid iron(III) chloride and hydrogen sulfide gas. 1Fe2S3 + 6HCl ® 2FeCl3 + 3H2S 1Fe2O3(s) + 2Al(s) ® 2Fe(s) + 1Al2O3(s)

See if you can translate this chemical equation into a word equation. K(s) + H2O(l)H2(g) + KOH (aq)

Answer Solid potassium reacts (+) with liquid water to produce () hydrogen gas and (+) aqueous potassium hydroxide