Given the mass (in grams) of a reactant A, first divide this by the molar mass of A to get the number of moles of A. Then balance the chemical reaction, and divide the number of moles of A by the coefficient of A in the balanced reaction. Next, find the coefficient of the product (B) in the reaction, and multiply this by the result from the previous operation. Finally, multiply by the molar mass of B to get the final answer in grams of the product B.