Introduction
This unit will introduce you to a quantitative approach to chemical reactions. That means we're going to use lots of numbers and do lots of calculations.
So far all our work has been qualitative - that means that we have recorded what was being mixed, then observed what was happening in a reaction and finally described it in words.
To use a quantitative approach we measure amounts of chemicals present and make predictions about the amounts of products produced in a reaction.
But, you may say to yourself, we have been measuring out amounts of substances involved in reactions. That is true, you have been measuring quantities, but you knew the amounts to use by using a recipe contained in your Chemistry book.
For example, take 2 g of copper and add 200ml of nitric acid.
That was a good approach to begin with and it worked well (as long as the person writing the recipe knew what they were doing). But if you are going to become a chemical recipe writer yourself, or more importantly to us, if you are to make predictions about the amounts of chemicals produced in reactions, you will need to know exactly how to work out what quantities are used up or produced in a reaction.
Calculation of the quantities involved in reactions is the subject of this unit.
When do people need to calculate quantities?
Leaving aside the needs of students in the laboratory, industrial processes often require a chemist to be able to calculate how much of a particular product is going to be produced or how much of a reactant will be needed in a chemical reaction. EZ and Comalco for example, cannot afford to guess how much of their product is going to be produced from the reactants they use, economically that would not be sound business. So they need to have a way to work out how much chemical they will need in each of their reactions and how much of their product will be produced for the money they spend.
Chemists monitoring the environmental effect of processes also need to know exactly how much of possible pollutants might be produced and what effect that might have on the environment. (Other examples where knowledge of quantities is necessary could also be suggested, I am sure.)