Stoichiometry

What the heck is stoichiometry? Stoichiometry: The determination of how much stuff you can make in a reaction from some given amount of reactant.

What does that mean? In the kitchen, we do a very simple kind of stoichiometry whenever we make ourselves lunch. For example, when we make a ham sandwich using the equation: 2 slices bread + 1 slice ham  1 ham sandwich We know that to make two ham sandwiches, we will need four slices of bread and two slices of ham. All we need to do is to look at the equation (usually in our heads, though) to know that.

In chemistry, the same thing is true. If we do the reaction: 2 H 2 + O 2  2 H 2 O To make 2 moles of water, we know that we’ll need to start with 2 moles of hydrogen and two moles of water. Likewise, if we want to make 4 moles of water, we’ll use 4 moles of hydrogen and 2 moles of oxygen. This is why chemical equations are handy!

Example: Ammonium sulfate is made by the reaction: 2 NH 3 + H 2 SO 4  (NH 4 ) 2 SO 4 If we want to make 150 grams of ammonium sulfate, how much ammonia will we need?

How do we solve this? From what we just saw, we can figure out what we want by doing the following calculations: Convert grams of ammonium sulfate to moles (we already know how to do this). Convert moles of ammonium sulfate to moles of ammonia (which we just learned can be done directly from the equation). Convert moles of ammonia to grams of ammonia (we already know how to do this).

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Another example: How many grams of carbon dioxide will be made when 100 grams of CH 4 burn in oxygen? CH O 2  CO H 2 O answer: 275 grams

Practice!