Conversions & Balancing Equations

Mr. Ramos

Conversion means to change something “appearance.”◦ Example: 1 foot = 12 inches ◦ Example: 1 meter = 100 centimeters

1ft = 12in is known as a conversion factor

Cancel the units of the “Given” with the units of the conversion factor’s denominator.

What are Conversions?

 

Conversion Examples

The gasoline in an automobile gas tank has a mass of 60.0 kg and a density of 0.752 g/cm3. What is its volume in cm3?

Chemistry Example

What is the mass of Hydrogen, Carbon, or Oxygen? ◦ Go to the periodic table and try to find the

corresponding unit associated with the mass of these elements.

Hydrogen’s mass is 1.01 what? Carbon’s mass is 12.01 what? Oxygen’s mass is 16.00 what?

Where are the UNITS?

Where are the Units?

The atomic mass unit (amu), or Dalton, is used to indicate the mass of atoms and molecules.◦ Hydrogen has a mass of 1.01 amu◦ Carbon has a mass of 12.01 amu◦ Oxygen has a mass of 16.00 amu

If, however, we have a fixed amount of any element that equals 6.022 x 1023, then the mass of that element is changed from amu to grams.

1 mole = 6.022 x 1023 (Avogadro’s Number)

Where are the Units?

The element hydrogen has a mass of 1.01 amu.◦ However, 1 mole of hydrogen has a mass of 1.01 grams.

The element carbon has a mass of 12.01 amu.◦ However, 1 mole of carbon has a mass of 12.01 grams.

The element oxygen has a mass of 16.00 amu.◦ However, 1 mole of oxygen has a mass of 16.00 grams.

Do you notice the pattern?

1 mole of anything contains 6.022 x 1023 particles

The Mole

1 mole of M&M’s = 6.022 x 1023 M&M’s◦ That’s a lot of M&M’s (Yummy)

1 mole of U.S. dollars = 6.022 x 1023 U.S. dollars ◦ I would be rich! YES!

1 mole of carbon = 6.022 x 1023 carbon atoms = 12.01 grams of carbon

The Mole: Avogadro’s #

6CO2 + 6H2O + Sunlight C6H12O6 + 6O2

The formula above represents the photosynthesis equation.

How many grams of glucose are produced when 12 moles of carbon dioxide are consumed?

Conversions Involving Moles

Sodium chloride, NaCl, forms by the following reaction between sodium and chlorine.◦ 2Na (s) + Cl2 (g) 2NaCl (s)

How many moles of NaCl result from the complete reaction of 3.4 mol of Cl2? Assume that there is more than enough Na.

Solve by Converting

Water is formed when hydrogen gas reacts explosively with oxygen as according to the following balanced equation.◦ O2 (g) + 2H2 (g) 2H2O (g)

How many moles of H2O result from the complete reaction of 24.6 mol of O2? Assume that there is more than enough H2.

Solve by Converting

How many moles of ammonia (NH3) are produced when 0.60 mol of nitrogen (N2) reacts with Hydrogen (H2)?◦ N2 (g) + 3H2 (g) 2NH3 (g)

Solve by Converting

For any closed system, mass cannot be created or destroyed.◦ Mass can only be transferred.

Law of Conservation of Mass

ReactantsProducts

Chemical equations must always be balanced.

6CO2 + 6H2O C6H12O6 + 6O2

Balanced Chemical Equations

Carbon = 6

Oxygen = 18

Hydrogen = 12

Carbon = 6

Oxygen = 18

Hydrogen = 12

Reactants Products

1. Write a skeletal equation by writing chemical formulas for each of the reactants and products.

SiO2 (s) + C (s) SiC (s) + CO (g)

Writing Balanced Chemical Equations

SiO2 (s) + C (s) SiC (s) + CO (g)

2. If an element occurs in only one compound on both sides of the equation, balance it first. If there is more than one such element, balance metals before nonmetals.

Begin with Si: 1 Si atom 1 Si atom◦ Si is already balanced

Balance O next: 2 O atoms 1 O atom◦ To balance O, put a 2 before CO (g)◦ SiO2 (s) + C (s) SiC (s) + 2CO (g)

Writing Balanced Chemical Equations

SiO2 (s) + C (s) SiC (s) + 2CO (g)

3. If an element occurs as a free element on either side of the chemical equation, balance it last. Always balance free elements by adjusting the coefficient on the free element.

Balance C: 1 C 3 C◦ To balance C, put a 3 before C (s)◦ SiO2 (s) + 3C (s) SiC (s) + 2CO (g)

Writing Balanced Chemical Equations

SiO2 (s) + 3C (s) SiC (s) + 2CO (g)

4. If the balanced equation contains coefficient fractions, clear these by multiplying the entire equation by the appropriate factor.

This step is not necessary in this example.

Writing Balanced Chemical Equations

5. Check to make certain the equation is balanced by summing the total number of each type of atom on both sides of the equation.

SiO2 (s) + 3C (s) SiC (s) + 2CO (g)

Writing Balanced Chemical Equations

Silicon = 1

Oxygen = 2

Carbon = 3

Silicon = 1

Oxygen = 2

Carbon = 3

C8H18 (l) + O2 (g) CO2 (g) + H2O (g)

Writing Balanced Chemical Equations: Solve

Fe (s) + 3HCl (aq) FeCl3 (aq) + H2 (g)

Writing Balanced Chemical Equations: Solve