how Many grams of element z

Question

137.34 grams of element X reacts with 67.41 grams of element Z to form a compound. How many grams of the same compound could be produced using 55.1 grams of element X with excess element Z?

Answer 1

The law of definite proportion, (Proust's law) states that a given chemical compound (in this case XZ) always contains its component elements in a fixed ratio (by mass).  The source of material or the method of preparation doesn't matter.  Thus, in the case presented, the fixed ratio by mass is 137.32g X/67.41 g Z = 2.037 as the X to Z ratio.  Simply use this ratio to find the answer to the question.

 

55.1 g X/?g ZY = 2.037

Z = 55.1g/2.037

Z = 27.05 g

So, you'd need 27.05 grams of Z to react with 55.1 g of X.

Based on the Law of Conservation of mass, the amount of product would be 27.05 g + 55.1 g = 82.2 g (to 3 sig. figs.)