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.
- 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 you know the mass, and you can use the periodic table to find atomic or molecular mass MR of that substance.
- With the moles formula above, you can remember it using the units in brackets too, like you would in general algebra: = and the g will cancel out. You are then left with = which cancels for mol
- 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).
- Whenever answering test questions involving gas volume, check the conditions of the reaction. DO NOT CONFUSE THE TWO!
- 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.