Warmup (5 minutes) 1. A “dozen” is what we call a “counting unit.” What are some other counting units? 2. Write the formula for aluminum sulfate 3. Do atoms ever disappear from our universe?

Equations and the Mole You will have another Memorization Quiz next class: ions again, and solubility rules too!

In science, a mole is how we count the number of a substance (like a dozen).

How much is a mole? The number of things in 1 mole has been determined to be: 6.02 x This is Avogadro’s Number (after the scientist who figured it out) is the number of atoms in 12 grams of carbon.

Is one mole always the same quantity? 1 mole silicon atoms 1 mole iodine atoms Mass = gramsMass = grams 6.02x10 23 atoms in each box Yes: for # molecules or atoms No: for mass

2Na(s) + 2H 2 O(l) → 2NaOH(aq) + H 2 (g) solidliquidaqueous gas 2 moles1 mole (no #) ReactantsProducts arrow = “yield”, “make”, “produce”, “form” Translate the equation into a sentence! 2 moles of solid sodium react with 2 moles of liquid water to yield 2 moles of aqueous sodium hydroxide and 1 mole of hydrogen gas (Why H 2 ?)

Diatomic Elements are: gaseous elements which are unstable if found as a single atom; H 2 O 2 F 2 Br 2 I 2 N 2 Cl 2 Write an equation: 2 moles of solid sodium react with 1 mole of chlorine gas to yield 2 moles of aqueous sodium chloride 2Na(s) + Cl 2 (g)  2NaCl(aq)

Write the equation: solid calcium reacts with aqueous hydrogen chloride to yield aqueous calcium chloride and hydrogen gas Ca(s) + HCl(aq) → CaCl 2 (aq) + H 2 (g) Is this equation balanced? Law of conservation of matter: in a chemical reaction, matter is neither created nor destroyed

A balanced equation obeys this law; it has equal numbers of each type element on both sides of the equation. “what goes in, comes out!” _____H 2 + _____ O 2  _____ H 2 O 122

Balancing Tips 1) Use a pencil, you might have to erase! 2) It helps to balance metal atoms first, H’s and O’s last! 3) Place whole-number coefficients in front of the formulas; NEVER change subscripts in the chemical formula. “1” is not completely necessary. 4) Multiply new coefficient times the subscript to count the total # atoms for that element on each side. (Example: 2H 2 = 4 hydrogen atoms total) It takes practice…you will not learn by watching!

__Al (s) + __Fe 2 O 3 (aq) → __Al 2 O 3 (aq)+ __Fe(s) Balancing Example: # AlOFe OOAl OOOFe Al

__C 2 H 4 + __O 2 → __CO 2 + __H 2 O 2 minutes! ____ N 2 + ____ H 2  ____ NH

Be Careful With Parentheses:  How many atoms are in: Mg(OH) 2 3Mg(OH) 2 # of Mg atoms: # of O atoms: # of H atoms: Mg(OH 2 )

 A hamburger is made of certain materials: Bun Lettuce Meat Bun  What would an equation for the synthesis of one hamburger look like? ____Bun + ____Lettuce + ____Meat  ____hamburger 2111

Mole Ratio Problems  If I wanted to make 20.5 hamburgers, how many buns would I need? ____Bun + ____Lettuce + ____Meat  ____hamburger hamburger (1 hamburger) (2 buns) = 41.0 buns How many hamburgers can I make if I had 17 meats (assuming I have enough of everything else)? 17 meats (1 meat) (1 hamburger) = 17 hamburgers

1N 2 + 3H 2  2NH 3 Translate the equation above into a sentence: If 1 mole N 2 reacts with 3 moles H 2, 2 moles NH 3 are produced. Write all the molar ratios possible given this equation The molar ratio compares the number of moles of each compound in an equation. I will sometimes say ‘molecules’ to simplify, although this is technically inaccurate. 1 mole N 2 3 moles H 2 1 mole N 2 3 moles H 2 1 mole N 2 2 moles NH 3 2 moles NH 3 3 moles H 2 2 mole NH 3 1 mole N 2 2 moles NH 3 3 moles H 2

If 2 moles of N 2 are used, how many moles of NH 3 will be produced in the reaction? 1N 2 + 3H 2  2NH 3 2 moles N 2 (2 moles NH 3 ) = 4 moles NH 3 (1 mole N 2 ) If you want 7.70 moles of NH 3, how much H 2 is needed? 7.70 moles of NH 3 (3 moles H 2 ) = (2 moles NH 3 ) 11.6 moles H 2 Warning: Sometimes you will have to balance the equation first!