Warm Up:

You are the owner of an ice cream parlor. A class of 20 small,ravenous children storm your shop, each demanding an ice cream sundae.  

One sundae requires 50 mL of chocolate syrup, 2 scoops (1 cup) of vanilla ice cream, and 1 cherry. If you have 600 mL syrup, 25 cups of ice cream, and 20 cherries, how many sundaes will you be able to make?

How is the recipe for making an ice cream sundae like a chemical equation? What type of reaction would this represent?

Ch. 9.1 Intro to Stoichiometry Stoichiometry - branch of chemistry that involves

calculating the amount of reactants consumed or products formed in a chemical reaction.

Before you can calculate quantities involved in a particular reaction, you must understand the significance of a chemical equation.

The coefficients can be interpreted 2 ways:

(a) particle interpretation

(b) mole interpretation

Particle Interpretation:

Coefficients represent the relative number of particles of each substance.

Example: 2 H2(g) + O2(g) --> 2 H2O(l)

2 molecules of H2 reacts with 1 molecule of O2 to produce 2 molecules of H2O

This is consistent with the law of conservation of mass.

Same number of each atom on both sides of the equation.

Mole Interpretation:

Coefficients can also represent the relative number of moles of each substance.

Example:

2 H2(g) + O2(g) --> 2 H2O(l)

2 moles of H2 reacts with 1 mole of O2 to produce 2 moles of H2

This is also consistent with the law of conservation of mass.

2 (2 g) + 32 g --> 2 (18 g)

36g --> 36 g

However, the coefficients in an equation DO NOT represent a mass relationship.

2 H2(g) + O2(g) --> 2 H2O(l)

2 g + 1 g not equal to 2 g

Mole Ratio A mole ratio is a conversion factor that relates the

amounts in moles of any two substances involved in a chemical reaction

Example:

2 Al2O3(l) --> 4Al(s) + 3O2(g)

Molar conversion Video

What Do You Think? Balance the following chemical equation

and provide all the possible mole ratios that can be derived from this equation. (Hint: there are six)

N2 (g) + H2 (g) --> NH3 (g)

EOC Sample Question ___ N2 + ___ O2 --> 2 N2O5

What quantities of nitrogen gas (N2) and oxygen gas (O2) will react completely to produce 2 moles of dinitrogen pentoxide (N2O5)?

A. 4 moles of N2 and 10 moles of O2

B. 4 moles of N2 and 5 moles of O2

C. 2 moles of N2 and 10 moles of O2

D. 2 moles of N2 and 5 moles of O2

The mole ratios can help us determine amount of reactants consumed or products formed in a particular chemical reaction.

Given moles of one substance in a reaction, we can use mole ratio to calculate the moles of another substance in the reaction.

Sample Problem

In a spacecraft, the carbon dioxide exhaled by astronauts can be removed by its reaction with lithium hydroxide, LiOH, according to the following chemical equation.

CO2(g) + 2 LiOH(s) --> Li2CO3(s) + H2O(l)

How many moles of lithium hydroxide are required to react with 20 mol CO2, the average amount exhaled by a person each day?

Your Turn In the reaction:

4 NH3 (g) + 6 NO (g) --> 5 N2 (g) + 6 H2O (g)

How many moles of NH3 are needed to produce 12.4 mol H2O?

Reflection

What is the most important thing you learned today?

What is a question you would still liked answered?

What is a way what you learned today connects with what you knew before?