Based on the balanced equation
2NBr3 + 3NaOH → N2 + 3NaBr + 3HOBr
calculate the number of NaBr formula units formed when 126 NBr3 molecules and 192 NaOH formula units react?
126 units of NBr3 react with 3/2 x 126 = 189 units of NaOH. There will be 3 units of NaOH unreacted.
189 formula units of NaBr will be formed.
The term "formula units" is new to me. I assumed that "formula units" means the same thing as moles, or any unit of mass divided by molecular weight.
Formula unit is essentially the same as molecule. Formula units come about because some don't like to call NaCl a mole or even NaCl as the molecular formula. Why. Because NaxClx is a better way of representing how Na and Cl2 combine to form NaxClx. There are no discrete NaCl molecules as in CO2, CS2, O2, etc. So they get around that problem by call NaCl a formula unit instead of a molecular unit or molecule or mole. CO2 is a formula unit as well as a molecular unit but NaCl is not both. Personally, I think it's a waste of time to try and be as picky as that. By the same reasoning, I would just as soon stick to molecular weight (instead of molar mass), weight instead of mass, etc etc. I think we confuse the students when we try to get too technical. Chemistry is already too technical for many students at the beginning level. Everyone KNOWS we mean mass when we say weight. We can become more picky at advanced levels. But alas, the trend is to be more picky early in the game.
To calculate the number of NaBr formula units formed, we need to use stoichiometry based on the balanced equation.
From the balanced equation:
2NBr3 + 3NaOH → N2 + 3NaBr + 3HOBr
We can see that 2 moles of NBr3 react with 3 moles of NaOH to produce 3 moles of NaBr.
Now, let's convert the given number of NBr3 molecules and NaOH formula units into moles.
Given:
Number of NBr3 molecules = 126
Number of NaOH formula units = 192
To convert molecules to moles, we need to divide the number of molecules by Avogadro's number. Avogadro's number is approximately 6.022 × 10^23 molecules/mol.
Number of moles of NBr3 = 126 molecules / (6.022 × 10^23 molecules/mol)
Number of moles of NBr3 = 2.09 × 10^-22 mol
Similarly, to convert formula units to moles, we divide the number of formula units by Avogadro's number. Since NaOH is an ionic compound, one formula unit represents one mole of NaOH.
Number of moles of NaOH = 192 formula units / (6.022 × 10^23 formula units/mol)
Number of moles of NaOH = 3.18 × 10^-22 mol
Now that we have the number of moles of NBr3 and NaOH, we need to use the stoichiometric coefficients to determine the moles of NaBr formed.
According to the balanced equation, 2 moles of NBr3 react to produce 3 moles of NaBr.
Using a ratio, we can calculate the moles of NaBr formed:
Number of moles of NaBr = (Number of moles of NBr3) x (3 moles of NaBr / 2 moles of NBr3)
Number of moles of NaBr = (2.09 × 10^-22 mol) x (3/2)
Finally, to convert the moles of NaBr to the number of NaBr formula units, we multiply by Avogadro's number:
Number of NaBr formula units = (Number of moles of NaBr) x (6.022 × 10^23 formula units/mol)
Number of NaBr formula units = (2.09 × 10^-22 mol) x (3/2) x (6.022 × 10^23 formula units/mol)
Evaluating this expression, we can calculate the number of NaBr formula units formed when 126 NBr3 molecules and 192 NaOH formula units react.