Law of Conservation of Mass and Balancing Chemical Equations

Let’s Review Counting Atoms Copy the following chemical formulas in your notes and count the TOTAL number of atoms. 1.4 K 2 SO 4 ________ 2.(NH 4 )PO 4 ________ 3.Ba(OH) 2 ________ 4.2 KNO 4 ________ 5.2 Ca 3 (PO 4 ) 2 ________

First Described the “Law of Conservation of Mass” Father of Modern Chemistry

Conservation of Mass Antoine Lavoisier found that the mass of the reactants and the products are equal, even when the states of matter change. Hg + O 2 HgO He started with: 10g of Mercury Oxide (HgO) He ended up with: and 9.3g Mercury… 0.7g Oxygen became a gas 10 g. = g...But what happened to the O 2 ?

This is the Law of the Conservation of Mass It states that: “Matter is neither created or destroyed, it only changes form.” These ‘changes’ include phase changes solid liquid gas The amount that you started with will be equal to the amount you end with MASS REACTANTS = MASS PRODUCTS

Lavoisier’s Chemical Equation: Hg (mercury) can exist by itself... but, oxygen will need to bond with another oxygen to make O 2 HgO  Hg +O2O2 2 2 To balance the atoms we need to: This balances the equation! Put the coefficient of 2 in front the product Hg. Put the coefficient of 2 in front of reactant HgO.

Not that easy? Let’s try... Easy, Right?

BALANCING CHEMICAL EQUATIONS

Four Steps to Balance Equations: 1. Set up your equation. Write the metals, nonmetals, oxygen, and hydrogen. 2. Count and then write the number of atoms you have on both sides. 3. Balance by changing the coefficients and recounting. 4. Start the process again if it still does not balance.

Before we begin balancing, we will look at a couple of rules. 1.You can only change the coefficients, and NOT the subscripts. 2.The coefficients must be whole numbers. (Ex. – 1, 2, 3, 4…)

CLASS PRACTICE H 2 + O 2  H 2 O ____ H 2 + ____ O 2  ____ H 2 O Mg + HCl  H 2 + MgCl 2 ____ Mg + ____ HCl  ____ H 2 + ____ MgCl 2 Na + HCl  NaCl + H 2 ____ Na + ____ HCl  ____ NaCl + ____ H 2 H 2 + O 2  H 2 O ____ H 2 + ____ O 2  ____ H 2 O Mg + HCl  H 2 + MgCl 2 ____ Mg + ____ HCl  ____ H 2 + ____ MgCl 2 Na + HCl  NaCl + H 2 ____ Na + ____ HCl  ____ NaCl + ____ H 2 Copy these in your notes.

Let’s kick it Up a Notch!! __ KClO 3  __KCl + __O 2 __ Na + __ H 2 0  __ NaOH + __ H 2 __ S 8 + __ O 2  __SO 3 Copy these in your notes

Independent Practice 1.__Fe + __ O 2  __Fe 2 + __O 3 2.__Cl 2 + __Li  __LiCl 3.__ ZnS + __ O 2  __ZnO + __SO 2 4.__ Cl 2 + __ NaI  __ NaCl + __ I 2