Stoichiometry

What’s that you said?

What is Stoichiometry?

Stoichiometry is the numerical relationships in chemical reactions.

Let’s build a Tricycle(aka FSW3HP2)

For each tricycle we need : 1 frame (F) 1 seat (S) 3 wheels (W) 1 handlebar (H) 2 pedals (P)

The “chemical equation” for building a tricycle would look like:F + S + 3W + H + 2P → FSW3HP2

Tiny Tyke Workshop

The Tiny Tyke workshop is scheduled to make 640 tricycles. How many wheels should be in the workshop to make these tricycles?

Analyze the knowns and unknowns:

Known: The # of tricycles we need to build = 640 tricycles Bal eq: F + S + 3W + H + 2P → FSW3HP2 This balanced equation represents the formation of a

single tricycle (FSW3HP2) Therefore TT needs to make 640 FSW3HP2

Unknown: number of wheels = ? Wheels

3 W1 FSW3HP2

We now solve for the unknown:640 FSW3HP2 3 W = 1920 W

1 FSW3HP2

So you need 1920 wheels to make 640 tricycles.

Does this make sense??

Tiny Tyke has decided to make 288 tricycles each day. How many seats, wheels and pedals are needed?

Do this as 3 separate problems: Set up your ratios first:

1 S 3 W 2P 1 T 1 T 1 T

Now plug in what you’re given:288 trikes 1 seat = 288 seats

1T

288 trikes 3 W = 864 wheels1 T

288 trikes 2 P = 576 pedals 1 T

Based on chemical equations and the law of conservation of matter

Must know the balanced chemical equation for the reaction we are studying first

You can determine the quantities of reactants and products in a chemical reaction from reaction stoichiometry

Stoichiometry

There are 4 types of reaction stoichiometry problems:

1. mole-mole problems: moles of A → moles of B

2. mole-mass problems: moles of A → moles of B → mass of B

3. mass –mole problems: mass of A → moles of A → moles of B

4. mass-mass problems: mass of A → moles of A → moles of B → mass of

B What step do they all have in common?

Mole ratio

The relationship between the number of moles of reactants and/or products in a chemical equation.

N2 (g) + 3 H2 (g) → 2NH3 (g)

The mole ratio of H to N is 3 : 1 So… for every 1 mole of nitrogen, I need 3

moles of hydrogen (and will produce 2 moles of ammonia)

Now lets Pracitce

In the Synthesis of water, if I start out with 42 grams of H2 and an excess of 02, how much water will I have at the conclusion of the reaction?

1. Write the equationH2 + O2 H2O

2. Balance the equation2H2 + O2 2H2O

3. Start with what you know4. 42 g H2

Now its your Turn!

Butane (C4H10) undergoes combustion.

Balanced Equation: __ C4 H10 + __ O2 __ CO2 + __ H2O How many grams of CO2 are produced

when 88 g of O2 are reacted with an excess of butane?