In this lesson, we will learn:
• To recognize
the format of stoichiometry test questions and calculations.
• To recall
the molar volume of gas at standard
temperature and pressure and its meaning.
to calculate number of moles of chemicals in reactions using mass, moles and
volume of gas.
• The units of mass is g
, the units of amount of atoms or molecules is mol
, and the units of atomic or molecular mass () is g/mol
(pronounced “grams per mole” sometimes written gmol
• The formula
can be used to calculate the number of moles
of a substance when given mass, and using the periodic table to find atomic or molecular mass
of that substance.
• With the moles formula above, you can treat the unit terms like you would in general algebra:
, where g cancels out.
• The molar volume of gas at standard temperature
(0°C, 273K) and pressure is 22.4 litres per mole
The molar volume of gas at room temperature
(25°C, 298K) and pressure is 24 litres per mole
Whenever answering test questions involving gas volume, check the conditions the reaction is occurring under
. DO NOT CONFUSE THE TWO TERMS.
• Stoichiometry calculations involve unit conversions
from one quantity given in the question to an unknown quantity:
To get to moles, use the equation and the molar ratios shown.
To get to volume, use the molar volume of gas constants.
To get to mass, use the atomic/molecular masses shown in the periodic table.