WHAT IS STOICHIOMETRY?
INTERPRETING BALANCED CHEMICAL
EQUATIONS
 STOICHIOMETRY IS THE STUDY OF THE
QUANTITATIVE, OR MEASURABLE, RELATIONSHIPS
THAT EXIST IN CHEMICAL FORMULAS AND
CHEMICAL REACTIONS.
 N2H4 + 2 H2O2 -> N2 + 4 H2O
 The coefficients can indicate the following:
 1 molecule N2H4 + 2 molecules H2O2 -> 1 molecule N2 + 4 molecules H2O
 1 mole N2H4 + 2 moles H2O2 -> 1 mole N2 + 4 moles H2O
 32 g N2H4 + 2(34 g) H2O2 -> 28 g N2 + 4 (18 g) H2O
HOW DO WE CALCULATE THE AMOUNT OF
PRODUCT?
WHAT IS A LIMITING REACTANT?
 The reactant that
limits the amount of
product formed
 The reactant that in
an experiment is all
used up
Percent Yield
 Measures the efficiency of a reaction carried out in
the lab
 Theoretical yield – the maximum amount of
product that can form during a reaction (calculated)
 Actual yield – how much actually forms
 Factors causing % yield to be less than 100




Reaction not completing
Impure reactants
Loss of product during filtration
Careless measurement
HOW DO WE DETERMINE PERCENT YIELD?
 Although you can
determine the
amount of product
that will be
produced in a
chemical reaction, in
reality, that
calculated amount is
not always the actual
amount obtained
from the reaction.
Thermochemical Equation
 Shows the amount of heat produced or
absorbed by a reaction
 Every reactant will have a certain heat
content, or enthalpy (H)
 The change in enthalpy (H) will tell us
if the reaction is exo or endothermic
Change in Enthalpy
 If H is positive, reaction is
endothermic (heat is a reactant)
 If H is negative, reaction is exothermic
(heat is a product)