Stoichiometry
Your Job
• Using the worksheet in your packet….
– Write what is in BLUE in the box titled “notes”
– Write the steps to solving problems and example
problems on bottom half of worksheet. If you
need more room, use the back of your packet.
What is stoichiometry?
• The study of the quantitative aspect of
chemical reactions
Why do we care?
• Just like a cookie recipe
needs the exact
amounts of ingredients
to make a perfect batch,
so do chemical
reactions!
• Using stoichiometry, we
can calculate how much
product you’ll produce
from a given amount of
reactants, or how many
reactants you need to
form a certain amount
of products.
Writing and using mole ratios
N2 + 3H2 -> 2NH3
-Balanced chem equations provide a lot of quantitative information.
-It relates particles (atoms, molecules, formula units) moles of a
substance, and masses.
-A balanced equation is essential to calculate amounts of reactants and
products.
-Mole ratio: conversion factor derived from coefficients of a balanced
chemical equation interpreted in terms of moles.
-In chemical calculations, more ratios are used to convert between
moles of reactant and moles of product.
Write the mole ratios for the formation of ammonia:
Try some!
Using Chemical Calculations
• 3 main types of chemical calculations
– Mole-mole
– Mass-mole, mole-mass
– Mass-mass
• All calculations will require a balanced
chem. equation and mole ratios
• Tips in solving problems:
– Always write your “given” first!
– Always set up your units so you can
cancel them out
– Place the units you want on top of
the conversion factor
Mole-Mole Calculations
N2 + 3H2 -> 2NH3
Given moles x # mol unknown = mol unknown
# mol given
• How many moles of ammonia are produced when .60 mol of nitrogen
reacts with hydrogen?
• How many moles of nitrogen are needed to produce 1.8 mol ammonia?
Moles-Grams (moles-mass) Calculations
N2 + 3H2 -> 2NH3
Given moles x # mol unknown x m. mass unknown
# mol given
1 mol unknown
= mass (grams) unknown
How many grams of nitrogen are needed to react completely with 2.5 moles of
hydrogen?
How many grams of ammonia are produced when .75 mole of hydrogen react
with an excess of nitrogen?
Grams-Moles (mass-moles) Calculations
N2 + 3H2 -> 2NH3
Given grams x 1 mole given
x
m. mass given (g)
# mol unknown
# mol given
=
# mole unknown
How many moles of nitrogen when combined with 27 grams hydrogen are needed to
form ammonia?
How many moles of hydrogen are needed to form 105 grams of ammonia?
Grams-Grams (mass-mass) Calculations
N2 + 3H2 -> 2NH3
Given grams x 1 mol given
x # mol unknown x m. mass unknown (g) = mass unknown(g)
m. mass given (g)
# mol given
1 mol unknown
Calculate the number of grams of ammonia produced by the reaction of 5.40g hydrogen
with an excess of nitrogen.
Calculate the number of grams of nitrogen when 55g hydrogen are added to form
ammonia.
How are we doing?
To lighten the mood…
• http://www.mybigcampus.com/items/babylaughing-hysterically-at-ripping-paper-original--710776
• http://www.mybigcampus.com/items/kapooy
a-autotune-remix-original-now-on-itunes--6511892
Practice makes perfect