Anthony T. answered • 05/02/21

Patient Math & Science Tutor

**2 NH3 + 3 CuO → 3 Cu + N2 + 3 H2O**

The first thing to be done is to balance the equation, but that has already been done.

The next thing is to determine what are you trying to calculate. This is grams of N2. Make a ratio of the # moles of N2 to the number of moles of CuO which is obtained from the coefficients of the molecules in the balanced equation:

1 mole N2 / 3 moles of CuO.

Next write that ratio and multiply by the given # of moles of CuO:

1 mole N2 / 3 moles of CuO x 1.2 moles CuO = 0.4 moles of N2 produced.

Note that moles of CuO cancels out leaving only moles of N2.

Now multiply the number of moles N2 produced by the ratio of the gram molecular mass of N2 to 1 mole N2:

28 g N2 / 1 mole N2 x 0.4 moles N2 = 11.2 grams N2 produced. Note that moles N2 cancel. When making these ratios, remember to put the thing you are trying to calculate in the numerator.