MOLE RATIOS IN CHEMICAL EQUATIONS

•

STOICHIOMETRY‘the study of the quantitative relationships

that exist in chemical formulas and reactions’

The study of the number of particles – moles – mass relationships in chemical reactions.

Why do chemists need Stoichiometry? Chemists often want to make a certain amount of a chemical. Stoichiometry

helps chemists figure out the “recipe” for making a certain amount of product.

+

N2(g) + 3H2(g) → 2NH3(g) Particle Relationships in a balanced chemicalequation

Mole Relationships in Chemical Reactions…k

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

The coefficients represent moles…

2NaCl 2Na + Cl2

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. 2H2(g) + O2(g) 2H2O(g)

2 : 1 : 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: N2(g) + 3H2(g) → 2NH3(g)

3H2 : 2NH3

• Unknown: 3.12 moles H2 : x moles of NH3

• Setup Equation: 2NH3/3H2 = x NH3/3.12H2

x NH3 = (2NH3)(3.12H2)/3H2

= 2.08 moles of NH3 produced

• 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 mol

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?

Step 3: Use the balanced equation to find the mole ratio of the given substance to moles of desired substance

Mole : mole nA = nB x CoefficientA

CoefficientB= moles calculated of given x moles of desired (coefficient of desired)

moles of given (coefficient of given)

0.8556 mol NaCl x 1mol Cl2 = 0.4278 mol of Cl2

2 mol NaCl

Use the Mole Path

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?

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

3. If you combust 250.0 g of nonane,C9H20 how many liters of oxygen are consumed to make the reaction go to completion? Assume STP.

196.7 g

152.5 g

611.1 L

Chalk it up to Molar Relationships Activity p301

HOMEWORK:

Mole Ratios and Stoichiometry Worksheet

p305 #7 & 8