How many moles of aluminum are required to react completely with 18 moles of H2SO4?

Step 1: Write the balanced reaction between Al and `~H_2SO_4` .

The balanced equation for this reaction is:

`~2Al` + `~3H_2SO_4` -> `~Al_2(SO_4)_3` + `~3H_2`

Step 2: Determine the given amount, unit, and substance.

The given amount, unit, and substance is: 18 moles of `~H_2SO_4` .

Step 3: Determine the final unit and substance.

The final unit and substance is: moles of Al.

Step 4: Determine the ratio of moles of Al to `~H_2SO_4` .

The ratio of moles between two substances can be described by the coefficients of the substances in the reaction. The coefficient of Al in the reaction is 2. The coefficient of `~H_2SO_4` in the reaction is 3. Therefore, the ratio of Al moles to `~H_2SO_4` is 2 to 3. 

Mole ratios can be written as fractions:

    2 moles Al/3 moles `~H_2SO_4`  OR  3 mole `~H_2SO_4` /2 moles Al

Step 5: Set up the calculation.

The calculation will take the general form:

    given amount x mole ratio

    18 mol `~H_2SO_4 ` x (2 moles Al/3 moles `~H_2SO_4`) = 12 mol of Al

Notice that the mole ratio is oriented such that moles of `~H_2SO_4` is on the bottom. This way, moles of `~H_2SO_4` cancel out and we are left with moles of Al.