Moles, mass and gas calculations  Stoichiometry
Moles, mass and gas calculations
Lessons
Notes:
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.
• Methods to calculate number of moles of chemicals in reactions using mass, moles and volume of gas.
Notes:
• The units of mass is g, the units of amount of atoms or molecules is mol, and the units of atomic or molecular mass ($M_R$) is g/mol (pronounced “grams per mole” sometimes written gmol$^{1}$).
• The formula: $n(mol) = \frac{mass(g)}{M_R (\frac{g}{mol})}$ 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 $M_R$ of that substance.
• With the moles formula above, you can treat the unit terms like you would in general algebra: $\frac{g}{\frac{g}{mol}}=mol$, where g cancels out.
• The molar volume of gas at standard temperature (0°C, 273K) and pressure is 22.4 litres per mole (22.4 L/mol).
The molar volume of gas at room temperature (25°C, 298K) and pressure is 24 litres per mole (24 L/mol).
$\circ$ 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:
$\circ$ To get to moles, use the equation and the molar ratios shown.
$\circ$ To get to volume, use the molar volume of gas constants.
$\circ$ To get to mass, use the atomic/molecular masses shown in the periodic table.

Intro Lesson
Recap of stoichiometry: Introduction

1.
Calculate the masses and volumes of reactants and products used in chemical reactions.
2C$_6$H$_{14\;(l)} +$19O$_{2\;(g)}$→12CO$_{2\;(g)} +$14H$_2$O$_{\;(g)}$ 
2.
Calculate the masses and volumes of reactants and products used in chemical reactions.
P$_{4\;(s)} +$5O$_{2\;(g)}$→P$_4$O$_{10\;(s)}$ 
3.
Calculate the volume and number of moles of reactants involved in chemical reactions.
2NH$_{3\;(aq)} +$NaOCl$_{\;(aq)}$→N$_2$H$_{4\;(aq)} +$NaCl$_{\;(aq)} +$H$_2$O$_{\;(l)}$