**Stoichiometry**

What do you HAVE?

(The GIVEN)

The problem will have a number in it, that is what you have. Pay attention to the UNIT.

ex:

"

13

grams

of HCl

react to form..."

"...will produce

15

liters

hydrogen gas

."

What do you WANT?

(The GOAL)

The question will also ask for something. Pay attention to the UNIT.

ex:

"

How many

moles

of carbon dioxide

are needed to..."

"...will form

how many

molecules

of ethane

?"

Find the correct pathway.

I know you might want to skip this,

BUT IT REALLY HELPS

. You should probably write the pathway at the top of your workspace.

Now do it!

In the last example, the pathway looks like this:

Volume A -> Moles A -> Moles B -> Mass B

Your work might look like this:

MASS A

(in grams)

VOLUME A

(in liters)

PARTICLES A

(in atoms, ions, molecules, or formula units)

MOLES A

1 mole A

22.4 liters A

1 mole A

6.02 x 10 particles A

23

1 mole A

molar mass A

# moles B in equation

# moles A in equation

MOLES B

MASS B

(in grams)

VOLUME B

(in liters)

PARTICLES B

(in atoms, ions, molecules, or formula units)

22.4 liters B

1 mole B

6.02 x 10 particles B

1 mole B

23

molar mass B

1 mole B

Say, for instance, the problem gives you a value in LITERS and asks for a value in GRAMS. You would follow the path:

Volume A -> Moles A -> Moles B -> Mass B

(Click through to see the path with conversion factors)

Find the units on the GIVEN and the GOAL on this chart, and follow the path from one to the other.

Make sense?

This chart works for ALL stoichiometry problems.

If you start or end with moles (as in a two or one step problem), you can completely ignore any irrelevant steps.

(Click to take another look at the whole chart.)

1 mole A

22.4 liters A

# moles B in equation

# moles A in equation

molar mass B

1 mole B

liters A x x x = grams B