(2.3)Conservation of Mass

(p148-149)

Law of Conservation of Mass During a chemical reaction, the total

mass and number of atoms of the reactants equals the total mass and number of atoms of the products.

Notice there are equal numbers of hydrogenhydrogen atoms and oxygen oxygen atoms on both sides.

Law of Conservation of Mass Recall for a chemical equation:

Reactant(s) Product(s)

Law of conservation of mass says that….

mass reactants = mass products

Law of Conservation of Mass-Example (Figure 2.20 p148)

Let’s count the atoms

Reactants Type of Atom Products

Na

H

O

Law of Conservation of Mass-Example (Figure 2.20 p148)

Let’s count the atoms

Reactants Type of Atom Products

2 Na

4 H

2 O

Law of Conservation of Mass-Example (Figure 2.20 p148)

Let’s count the atoms

Reactants Type of Atom Products

2 Na 2

4 H 4

2 O 2

Law of Conservation of Mass-Example (Figure 2.20 p148)

Let’s count the atoms

Reactants Type of Atom Products

2 Na 2

4 H 4

2 O 2

This is a balanced equation!

How To Count Atoms

The symbol of an element represents one atom of that element. Eg. Ca = one calcium atom

Counting Atoms

A subscript is a number written at the lower right corner behind the symbol of an element. If there are more than one atoms of the element in the molecule, then a subscript is used to indicate the number of atoms. N2 = 2 atoms of nitrogen CO2 = 1 atom of carbon & 2 atoms of

oxygen

Counting Atoms

A subscript outside a bracket multiplies all the elements inside the bracket Ba3(PO4)2

3 atoms of barium 1 x 2 atoms of phosphorous = 2 4 x 2 atoms of oxygen = 8 TOTAL atoms = 13

Counting Atoms

A coefficient is a number written in front of a chemical symbol and indicates the number of atoms of the element. 3 C = 3 carbon atoms 3 O2 = 3 molecules of O2 or 6 oxygen

atoms

COUNTING ATOMS

A coefficient is a number written in front of a chemical formula and indicates the number of molecules of that compound. 2 H2O = 2 molecules of water So H2O + H2O = 4 hydrogen atoms

& 2 oxygen atoms

Classwork

Worksheet 2.3 (C)Let’s practice examples 1-3 together

and then you can complete page 2