Conservation of Mass Balancing Chemical Equations 1/19/16

Daily Expectations 1.Wear your badge at all times. Not having your badge will result in an office referral. 2.Bring your tablet and journal to class everyday. 3.Cell phone use is prohibited in this classroom.

Stoichiometry (stoy-key-OM-uh-tree) stoichiometry - the area of study that examines the quantities of substances consumed and produced in chemical reactions Built on an understanding of atomic masses, chemical formulas, and the law of conservation of mass 3

Balancing Equations Law of Conservation of Matter: – In a chemical reaction, matter can be neither created nor destroyed. – In a chemical reaction, the amount of reactants equal the amount of products. –

Balancing Equations Paraphrase: Law of Conservation of Atoms: – The number of atoms of each type of element must be the same on each side of the equation.

Diatomic elements - Elements that are present in the gaseous state in nature as molecules composed of two atoms. These elements cannot exist in nature as a single atom. Hydrogen, Nitrogen, Oxygen, Fluorine, Chlorine, Bromine, Iodine Written like: – H 2, N 2, O 2, F 2, Cl 2, Br 2, I 2

Chemical Equations Chemical equations are concise representations of chemical reactions. “reacts with” “produces” or “yields” “and” 7

Anatomy of a Chemical Equation CH 4 (g) + 2 O 2 (g) CO 2 (g) + 2 H 2 O (g) 8 Reactants appear on the left side of the equation. Products appear on the right side of the equation.

Anatomy of a Chemical Equation The states of the reactants and products are written in parentheses to the right of each compound. (g) = gas(l) = liquid(s) = solid(aq) = aqueuos (water) solution Sometimes, reaction conditions such as heat, symbolized Δ, are written above or below the arrow. CH 4 (g) + 2 O 2 (g) CO 2 (g) + 2 H 2 O (g) 9

Anatomy of a Chemical Equation Coefficients are inserted to balance the equation. balanced equation – must have equal # atoms on each side of the arrow (The coefficient 1 is left off; no coefficient = understood 1) CH 4 (g) + 2 O 2 (g) CO 2 (g) + 2 H 2 O (g) 10

Subscripts and Coefficients Give Different Information Subscripts tell the number of atoms of each element in one molecule. 11

Subscripts and Coefficients Give Different Information Subscripts tell the number of atoms of each element in one molecule. Coefficients tell the number of molecules. To find the # of each type of atom, multiply the coefficient by each subscript. 12

Examples How many of each type of atom are there in the following formulas? a)3 Fe 2 O 3 b)4 Na 2 CO 3 c)Ba(ClO 3 ) 2 d)3 (NH 4 ) 3 PO 4 13

Balancing Chemical Equations Steps to follow 1.Determine the formulas of reactants and products 2.Write an unbalanced equation 3.Insert the coefficients that will provide equal numbers of atoms on each side of the arrow 14

Guidelines for balancing equations: a. NEVER change or add subscripts (changes identity of chemical) Adding a coefficient only changes the AMOUNT of a substance, rather than its identity 2 H 2 O = 2 molecules of water 3 H 2 O = 3 molecules of water b.Balance only one element at a time. c.Balance elements other than H and O first d.Use the smallest whole-number coefficients Ex: Zn + 2 HCl  ZnCl 2 + H 2 good 2 Zn + 4 HCl  2 ZnCl H 2 not good e.Balance as a group those polyatomic ions that appear unchanged on both sides of arrow CaO + HNO 3  Ca(NO 3 ) 2 + H 2 O (unbalanced) 15 Guidelines: Balancing Chemical Equations

Balancing Chemical Equations: Question… Which of the following would be the correct way to balance the oxygens in a chemical equation? a) adding a subscript 2 to the end of CO to give CO 2 or b)adding a coefficient in front of the formula to give 2 CO 16

Balancing Chemical Equations Fe 3 O 4 (s) + H 2 (g) Fe(s) + H 2 O(l) (unbalanced) Work on one element at a time. Don’t change the subscripts – only add coefficients. F: Fe 3 O 4 (s) + H 2 (g) 3Fe(s) + H 2 O(l) O: Fe 3 O 4 (s) + H 2 (g) 3Fe(s) + 4H 2 O(l) H: Fe 3 O 4 (s) + 4H 2 (g) 3Fe(s) + 4H 2 O(l) Check that all atoms are balanced, and they are! 17

Examples Balance the following equations: a)AgNO 3 + CaCl 2  Ca(NO 3 ) 2 + AgCl b)P + O 2  P 4 O 10 c)C 9 H 20 + O 2  CO 2 + H 2 O 18