1.  Although chemical changes occur, mass is neither created nor destroyed in a chemical reaction  Mass of reactants equals mass of products mass reactants = mass products A + B  C

3.  In an experiment, 10.00 g of red mercury (II) oxide powder is placed in an open flask and heated until it is converted to liquid mercury and oxygen gas. The liquid mercury has a mass of 9.26 g. What is the mass of the oxygen formed in the reaction? Mercury (II) oxide  mercury + oxygen Mmercury(II) oxide = 10.00 g Mmercury = 9.26 Moxygen = ? GIVEN: Mercury (II) oxide  mercury + oxygen M mercury(II) oxide = 10.00 g M mercury = 9.26 g M oxygen = ? WORK : 10.00 g = 9.26 g + m oxygen M oxygen = (10.00 g – 9.26 g) M oxygen = 0.74 g mass reactants = mass products

4.  In any chemical reaction, the final mass of the products ALWAYS equals the original mass of the reactants.  In other words – in a chemical reaction, mass cannot be added or gained.  The atoms on one side of the equation MUST balance with the atoms on the other side of the equation!

5.  This law was developed by a French chemist named Antoine Lavoisier. Lavoisier carefully measured the mass of the reactants and products when carrying out chemistry experiments.  He noticed that in every case, the mass of the reactants was ALWAYS equal to the mass of the products.

6.  This means that the number of atoms of a certain element in a reactant must equal the number of atoms of that element in the product.  For example: Na(s) + Cl 2 (g)------->NaCl(s) Reactants Products

7. Mass is neither created nor destroyed during chemical or physical reactions. Total mass of reactants = Total mass of products Antoine Lavoisier

8.  Consider the following balanced chemical reaction  CaCO 3 ----------> CaO + CO 2  In this reaction the mass of CaCO 3 must equal the combined mass of the CaO and CO 2.  SO, if you know the mass of the reactants you automatically know the mass of the products and vice-versa.

9.  Step 1- fill in the masses under the balanced equation as follows and make them equal each other and solve for X CaCO 3 ----------->CaO + CO 2 200g = (X)g + 88g 200g – 88g = 112g mass of CaO produced

10.  If 72 grams of water (2 H 2 O )and 64 grams of oxygen(O 2 ) are produced, what mass of H 2 O 2 decomposed?  a. 72 grams  b. 136 grams  c. 64 grams  d. Not enough information given