Thursday, November 10, 2016


Students, HERE is the brief Power Point Notes given in class which introduces the technique of 'mapping the equation':

This technique is complimentary to the fractional setups which we have been practicing for weeks, setups that allow chemists to convert units via cancellation:

Mapping the equation is very helpful in solving more complex, real-world problems in which the order of operations is important:

In these sort of problems, you should map the equation FIRST, then use the map as clues on how to set up the order of your fractional terms.  

Considering the mapped equation above, let's imagine that we are given 72 grams of hydrogen gas (H2), and we want to know how many grams of ammonia (NH3) can be produced in this reaction . . . .

The map tells us that after we write down the given amount as the first term, the second term should use the molar mass of hydrogen gas (2.02 g/mol), expressing it as a fractional term.   The third term, the mole ratio, we get from the balanced equation:  it tells us that for 3 moles of  on the reactant side, we should have 2 moles of  on the product side.   Finally, to convert from moles to grams, we use another molar mass, the molar mass of ammonia (17.04 g/mol ).

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