MOLE RATIOS IN CHEMICAL EQUATIONS

STOICHIOMETRY the study of the quantitative relationships that exist in chemical formulas and reactions

Particle Relationships in a

•

Balanced Chemical Equation

The Haber Process o N 2(g) + 3H 2(g) → 2NH 3(g) o 1 molecule of nitrogen + 3 molecules of hydrogen → 2 molecules of ammonia o 10 molecules of nitrogen + 30 molecules of hydrogen → 20 molecules of ammonia

Mole Relationships in Chemical Reactions…

The coefficients in a balanced equation give the relative amounts (in moles) of reactants and products.

The coefficients represent moles…

2NaCl



2Na + Cl 2 There are ____ moles of salt.

There are ____ moles of sodium.

There is ____ mole of diatomic Cl.

WHAT IS A MOLE RATIO?

It is the ratio amounts of the entities in a chemical reaction.

ex. 2H 2(g) + O 2(g)

2 : 1 :

2H 2 O (g)

2 Let’s Make Some Smore’s!!!

DETERMINING AMOUNTS USING MOLE RATIOS...

• • •

Using Ratios to Solve Problems

• Use known ratio to find out unknown.

o E.g. How many moles of ammonia can be produced from 3.12 moles of hydrogen?

Known

:

Unknown

: N 2(g) + 3H 2(g) → 2NH 3(g) 3H 2 : 2NH 3 3.12 moles H 2 : x moles of NH 3

Setup Equation

: 2NH 3 /3H 2 x NH 3 = x NH = (2NH 3 3 /3.12H

2 )(3.12H

2 )/3H = 2.08 moles of NH 3 produced 2 • Mole ratio method can also be used.

EXAMPLE 1: If you start with 50.0g of NaCl, how many grams of chlorine are produced when the salt is decomposed?

Step 1: Write a balanced chemical equation.

EXAMPLE 1: If you start with 50.0g of NaCl, how many grams of chlorine are produced when the salt is decomposed?

Step 2:

Find the number of moles of the given substance n = m/ MM

MM(NaCl) = 22.99 g + 35.45g = 58.44g/mol n = 50.0 g / 58.44 g/mol = 0.8556 moles Don’t round until the end!!!!!!!!!!!!!!!!!!!

EXAMPLE 1: If you start with 50.0g of NaCl, how many grams of chlorine are produced when the salt is decomposed?

Use the balanced equation to find the mole ratio of given substance to moles of desired substance Mole : mole problem = moles calculated of given x moles of desired moles of given

0.8556 moles NaCl x 1mole Cl 2 2 moles NaCl = 0.4278 moles of Cl 2

EXAMPLE 1: If you start with 50.0g of NaCl, how many grams of chlorine are produced when the salt is decomposed?

Convert moles of desired substance to whatever quantity(mass, volume or particles) is desired

EXAMPLE 2: What amount of oxygen is required to react completely with 6.4 x 10 -2 mol of aluminum to produce aluminum oxide?

Learning check

1.

If you decompose 500.0 g of sodium chloride, how many grams of sodium are produced? 196.7 g 1.

If you react 450.0 g of copper (II) nitrate with excess calcium, how much copper (II) is produced. 2.

If you combust 250.0 g of nonane,C 9 H 20 152.5 g how many liters of oxygen are consumed to make the reaction go to completion? Assume STP. 611.1 L

• Chalk it up to Molar Relationships Activity o p301

HOMEWORK:

Mole Ratios and Stoichiometry Worksheet p305 #7 & 8