March 2nd

All about STOICHIOMETRY!

Don't let its name daunt you! Stoichiometry is actually very simple, once you understand it!

Basically, stoichiometry refers to the measurement behind the different quantities of the reactants annd the products. You can think of it as the math behind the chemistry!

MATH! IT'S EVERYWHERE!

In stoichiometry, the chemical equations are always in balance. What does this mean? It means we use a term called the mole ratio!

Let's try a few sample problems.

1 Zn (s) + 2 HCl (aq) ---> 1 ZnCl (aq) + 1 H2 (g)

Now, look at the numbers in front of each element. They are 1:2:1:2. That is the mole ratio! This means that ONE molecule of zinc reacts with TWO molecules of hydrogen chloride to produce ONE molecule of zinc chloride and ONE molecule of hydrogen gas.

C2H5OH + 3O2 ---> 2CO2 + 3H2O

In this one, the mole ratio is what?

You guessed it! 1:3:2:3

Okay, now we're going to get down to some real work! Using the equation given above, do these problems, then check your solution.

OH AND ONE MORE THING: SIG FIGS IS ALWAYS RELEVANT!!! DON'T FORGET YOUR SIG FIGS!!!

Formula: 1 Zn (s) + 2 HCl (aq) ---> 1 ZnCl (aq) + 1 H2 (g)

Question: If a mad scientist had 0.270 moles of hydrogen chloride, how many moles of hydrogen gas will come out of the reaction?

Answer:

0.270 mol Zn x 1 mol H2 / 2  mol Zn

= 0.135 mol H2

Formula: C2H5OH + 3O2 ---> 2CO2 + 3H2O

Question: If the same mad scientist had 5.2 mols C2H5OH, how many mols of water could he make?

Answer:

5.2 mols C2H5OH x 3 mol H2O / 1 mol C2H5OH

= 15.6 mol H2O, but with sig figs = 16 mol H2O

Got it?

Now, here's a handy dandy website for you to practice some more STOICHIOMETRY! Good luck, my budding scientists!

Stoichiometry in All Its Beauty

Always make sure that the equation is balanced! It might not always be balanced FOR you in a test/quiz situation!