Unit 5 - Stoichiometry

What is stoichiometry?

calculation involved with quantities in chemical equations/reactions

What is the fundamental unit for counting particles and conversions?

mole

What is Avogadro’s number?

6.02 × 10²³

How many particles are in one mole of a substance?

6.02 × 10²³ particles

What is the mass of a mole called?

• gram formula mass

• molecular weight

• formula weight

• etc.

What are the mole conversions (“triangle”)?

grams ←→ moles ←→ # of particles / liters

What do you use to convert grams ←→moles?

gfm / molar mass

What do you use to convert moles ←→# of particles?

Avogadro’s #

What do you use to convert moles ←→liters gas?

22.4 (number of L in a mole)

How many liters are in one mole of a gas?

22.4 L

What is the formula for percent composition by mass?

(# of atoms)(gfm) / (gfm of compound) * 100

OR

part / whole * 100

What is an empirical formula?

formula of a compound that gives the simplest whole number ratios of atoms

(ex: CH₂)

What is a molecular formula?

shows the # of each type of atom in a molecule

(ex: C₆H₁₂O₆)

How do you find the empirical formula for a compound?

(1) convert % to grams

(2) convert grams to moles

(3) using the atom with the smallest moles, divide the moles of the other atoms

(4) round to nearest whole #

How do you convert the empirical formula to the molecular formula?

• (empirical gfm)_x = molecular

• x = whole #

• multiply the empirical formula by x

What are the three things that chemical reactions must conserve?

mass, energy, and charge

What do you need to do before doing any calculations with a chemical equation?

BALANCE IT!

What are the five main types of chemical reactions?

synthesis, decomposition, single replacement, double replacement, combustion

What does a synthesis reaction look like?

A + B → C

What does a decomposition reaction look like?

C → A + B

What does a single replacement reaction look like?

A + BC → AC + B

What does a double replacement reaction look like?

AB + CD → AD + CB

What is a combustion reactions?

when a substance that reacts with oxygen gas releases CO₂, H₂O, and energy (light/heat)

What is a complete ionic equation?

chemical equation that shows the disassociated aqueous ions

What is a net ionic equation?

chemical equation that shows the ions involved in the reaction

What are spectator ions?

ions that are no involved in a reaction

(they appear on both sides of the equations)

What are the three gases involved with wooden splints and what do they do?

• O₂ → glowing

• H₂ → “pop” sound

• CO₂ → burning/puts out the flame

What are the three tricksters (decompose naturally as products)?

• H₂CO₃ →H₂O + CO₂

• H₂SO₃ → H₂O + SO₂

• NH₄(OH) → H₂O + NH₃

What do the coefficients in a chemical equation tell you?

the mole ratio

What is a limiting reactant/reagent?

the reactant that runs out before the others, which determines the amount of product that can be made

What is an excess reactant/reagent?

reactant that has leftovers; there’s more than enough

How do you determine the limiting reactant?

find the number of moles needed of a reactant to react with the other reactant and compare with what the amount given

What is the percent yield formula?

% yield = actual yield / theoretical yield * (100)

What is theoretical yield?

the amount of product that should be produced

What is actual yield?

the amount of product produced when the reaction is run

Why do actual and theoretical yield differ?

they differ due to many factors such as temperature, error, measurements, etc.

What does it mean if you have a % yield greater than 100%?

contaminants most likely got in the way, increasing the theoretical yield