CHEMISTRY COMMUNITY

So Dr. Lavelle stated that we should begin balancing the equation by balancing the element present in the least number of reactants/products.

For example P4O10 + H2O = H3PO4 ; we should start by balancing either phosphorus or hydrogen since both are in two reactants/products.


Next, both phosphorus and hydrogen are shown to have 5 atoms total in the equation. What then would we do to determine which element gets balanced first?

I assume it would just be be based on what would be easier to balance first. I think it's just a strategy, not really a rule.

There’s no really strict guideline to choosing which to balance first. What you said is correct; you balance either hydrogen or phosphorus first since oxygen appears in both reactants and thus harder to balance. While hydrogen and phosphorus have equal number of atoms, I would start with phosphorous since there are 10 oxygens in P4O10. Such a large number would be difficult to work with if you have to balance P4O10 at the end. Saving the water molecule at the end will be much easier to balance since there is only one oxygen.

Yes I think it's just a guideline to follow to make it easier. I think when he says balance first the element that appears the least, he means the amount of times in the equation, not the number of moles.

Also, it's always easier to balance elements other than Carbon, Hydrogen and Oxygen first and then tackle those three in the order. The other elements usually appear in lower quantities and if you leave C H and O for the end, you may find that they may even be balanced already.

It’s always just easy to balance elements that are not all over the place. For example balancing phosphrous would be easier than oxygen in this case...

There really is no strict rule to follow when choosing an element to balance first, but like Dr. Lavelle stated, the elements with the least amount of moles are the easiest way to start. In this case, since there are 2 elements with the same amount of moles, I would start with the phosphorous because many times, common elements like oxygen tend to appear in larger amounts.

For F3 are we going to be expected to know the molecular formula for nitric acid or is this a later topic?

When finding the molar mass of a molecule after balancing the equation, do you ignore the stoichiometric coefficients? For example, 4NH3 would you multiply by 4 or just find the molar mass of NH3?

In response to the question about whether we need to know the molecular formula of nitric acid:
Dr. Lavelle may give us the formulas on the first test, but it is a good idea to become familiar with the nomenclature of compounds (see fundamentals section D). For example nitric acid is a polyatomic oxoacid (acidic molecular compound that contains oxygen) and has the polyatomic ion Nitrate in it. With oxoacid's that have a polyatomic acid in it that end with the suffix -ate (as Nitrate does), the acid name ends with the suffix -ic. So Nitrate becomes Nitric acid.

In response to the question about finding molar masses in a balanced equation:
The stoichiometric coefficients don't affect the molar mass of the compound, so the 4 in your example shouldn't be used in the calculation of the molar mass of NH3. The stoichiometric coefficients tell you how many moles of that compound is needed for that reaction, while the molar mass is the grams per mole.

There is no specific way/process to balance a chemical equation however you will find that balancing the element that appears the least is the easiest way to start and ending with the element that is shown the most. Many times Oxygen is the last element you balance since it shows up the most in many reactions.