Ammonia Gas • Ammonia Gas (NH ) and Saturn: Figure 12.6 (pg ...

Ammonia Gas

• Ammonia Gas (NH3) and Saturn: Figure 12.6 (pg. 362) ‒ Visible clouds of condensed ammonia surround several planets: Jupiter, Saturn and Uranus ‒ The atmosphere’s are so cold that the clouds of ammonia consist of frozen ammonia droplets!

Stoichiometry 12.2 Writing and Using Mole Ratios

Mole Ratios

• Stoichiometry ‒ Using chemical equations to calculate chemical quantities

• Mole ratio:

‒ Conversion factor derived from the coefficients in a balanced equation ‒ Used to solve many stoichiometric calculations ‒ Used when converting from the amount of one substance to amount of another

Stoichiometry

• What To Expect ‒ The most common stoichiometric problem will present you with a certain amount of a reactant and then ask how much of a product can be formed. Here is a generic chemical equation: 2A + 2B → 3C ‒ Here is a typically-worded problem: Given 20.0 grams of A and sufficient B, how many grams of C can be produced?

Stoichiometry • Skill Set Required for Stoichiometry!  Write chemical formulas correctly (9)  Calculate molar masses (10)  Balance and interpret equations (11,12.1)  Write and use mole ratios (12)  Convert between grams and moles of a substance. “Use molar mass!” (10)  Use additional conversion factors related to one mole: (10) • 1 mol = 22.4 L gas • 1 mol = 6.02 x 1023 particles

Mole Ratios • Writing mole ratios

N2(g) + 3H2(g) → 2NH3(g) o 6 mole ratios that may be used as conversion factors can be written from this equation

• N2(g) + 3H2(g) → 2NH3(g) ‒ 6 conversion factors:

• Write 6 mole ratios based on the following equation: 4Al + 3O2 → 2Al2O3

Stoichiometry

• Mole to mole conversion problems ‒ Use mole ratios from balanced chemical equations as conversion factors to convert between moles of one substance and moles of another

Stoichiometry

• Use problem solving steps and write complete units (mol Al) 1. What is the unknown? 2. What is the known? 3. What are the conversion factors needed? 4. Do the math 5. Finishing steps: sig figs, units, scientific notation

Stoichiometry

• Example: Mole-mole conversion ‒ How many moles of ammonia are produced when 0.60 mol of nitrogen reacts with hydrogen? ‒ N2(g) + 3H2(g) → 2NH3(g) • What is the unknown? • ? mol NH3

− What is the known quantity? • 0.60 mol N2

− Set up the problem: choose conversion factor

• What conversion factor (mole ratio) do you need to solve this problem? ‒ N2(g) + 3H2(g) → 2NH3(g)

• Do the math! • Don’t forget finishing steps.

• Calculate the number of moles of nitrogen needed to make 7.24 mol of ammonia. ‒ N2(g) + 3H2(g) → 2NH3(g)

• Calculate the number of moles of hydrogen needed to make 7.24 mol of ammonia. • N2(g) + 3H2(g) → 2NH3(g)

• 4Al + 3O2 → 2Al203

• How many moles of Al are needed to form 3.7 mol of Al203

• Mole – mole conversions are one step in more complex stoichiometric problems: Learn how to do them!!!!!!

• 4Al + 3O2 → 2Al203 ‒ How many moles of O2 are required to react completely with 14.8 mol Al?

• 4Al + 3O2 → 2Al2O3 ‒ Calculate the number of moles of 2Al2O3 formed when 0.78 mole of O2 reacts with Al.

• Homework: ‒ Q 40, pg 379 ‒ Read pg. 360-362 ‒ Study Sample problem 12.3, pg. 361