In older versions of Word this appears as the Layout tab of the Table Tools contextual tab in the Ribbon. However it will not be very easy and could be very time consuming. Now you can see the chemical form in the sidebar if you click the Chemistry Navigator button and can choose to insert the diagram into the document.
Select Insert Equation or press Alt.
Type 21cc then press ALT and X together no space after 21cc. You got some nice equilibrium arrows. For example for the Greek letter theta type theta and press the space bar to convert it. Simply select the word right-click select Convert to Chemistry Zone and then click on its name.