Question

Consider the following reaction sequence:
  $ {S_8}(s) + 8{O_2}(g) \to 8S{O_2}(g) \\
  2S{O_8}(g) + {O_2}(g) \to 2S{O_3}(g) \\ $
How many grams of $ S{O_3} $ are produced from one mole $ S{O_8} $ ?
 $ A.1280g \\
B.690g \\
C.640g \\
D.320g \\ $

Answer 1

Hint: Weight of the compound is equal to the product of number of moles and molar mass of the compound.
So, Wt. of compound $ = $ no. of moles $ \times $ molar mass.
Number of moles of $ S{O_3} $ produced by the $ 2 $ moles of $ S{O_2} $ is equal to $ 2 $ moles.

Complete step by step solution:
In the given question, first we see the first equation;
 $ {S_8}(s) + 8{O_2}(g) \to 8S{O_2}(g) $
Here we have one mole of $ {S_8} $ .
According to the reaction given, one mole gives $ 8 $ moles of $ S{O_2} $ .
Further,
Coming to the second equation;
 $ 2S{O_8}(g) + {O_2}(g) \to 2S{O_3}(g) $
Number of moles of $ S{O_3} $ produced by the $ 2 $ moles of $ S{O_2} $ is equal to $ 2 $ moles.
Therefore the number of moles of $ S{O_3} $ produced by eight moles of $ S{O_2} $ is equal to eight moles.
Also we know that,m
Weight of the compound is equal to the product of the number of moles and molar mass of the compound.
So, Wt. of compound $ = $ no. of moles $ \times $ molar mass
Therefore the weight of $ S{O_3} $ in eight moles is equal to,
$ 8 \times 80 \\
   = 640g $
 (Since molar mass of $ S{O_3} $ $ = 80g $ )
Hence $ 640grams $ of $ S{O_3} $ are produced by one mole of $ {S_8} $ .
So the correct option is C.

Note:
A mole is basically a conventional unit.it consists of many fundamental units of chemistry such as ions, molecules. Weight of the compound is equal to the product of the number of moles and molar mass of the compound.
So, Wt. of compound $ = $ no. of moles $ \times $ molar mass.
Molar mass- defined as mass in grams of one mole of a substance. Units of molar mass are grams per mole.