How can a slow rate of reaction lead to the actual yield of the reaction being less than the theoretical yield?

There are many things you might do to increase your yield:

1. Limit the number of transfers. Every time you transfer a component to another container, you lose some of the compound.

2. Add more of one reactant. If your reaction is an equilibrium reaction, use a large excess of the cheapest reactant.

3. Remove a product as fast as it forms. Removal of product forces the position of equilibrium to the right and increases the yield.

4. If your reactants are gases and you have fewer moles of gaseous products, increase the pressure.