Notice that a chemical equation gives both qualitative information (what things react to give what products) and quantitative information (how much stuff is produced if a particular amount of stuff reacts). This gives rise to various practical applications.
First need to find moles of CH_{4}:
MW = 12.01 + 4 (1.008) = 16.04
Moles of CH_{4} = 475.5 g / 16.04 g/mol = 29.64 mole.
Next need balanced equation:
CH_{4} + 2 O_{2} CO_{2} + 2 H_{2}O
Note from the equation we have a 1:1 ratio of moles methane to mole carbon dioxide
So we have 29.64 moles CO_{2}
& MW of CO_{2} = 12.01 + 2 (16.00) = 44.01
and (29.64 mol)(44.01 g/mol) = 1.304 kg
Let's look at a slightly more complicated reaction.
Asking question of what is the maximum amount of something which can be produced from a given mixture of stuff. This is a fairly straight-forward sort of problem in the day-to-day world, but seems to cause a great deal of difficulty for lots of folks in chemistry. Let's start by looking at a non-chemical problem:
Consider you have to make a bunch of sandwichs for a party. The equation for the sandwichs (in slices) is:
2 Bread + 1 Cheese + 1 Meat 1 Sandwich
You have a 32 oz loaf of bread, 22 oz of sliced cheese and 32 oz of sliced meat. If bread slices weigh 1/2 oz, cheese slices 3/4 oz and meat slices 1 oz, how many sandwichs can you make?
Look at how many sandwichs can be made from each ingredient:
- If bread limits: (32 oz bread)(2 slices bread/oz bread)(1 sandwich/2slices bread) = 32 sandwichs
- If cheese limits: (22 oz cheese)(1 slice cheese/3/4 oz cheese)(1 sandwich/slice cheese) = 29.3 sandwiches
- If meat limits: (32 oz meat)(1 slice meat/oz meat)(1 sandwich/slice meat) = 32 sandwiches
Cheese limits and we can make 29 sandwichs.
Fe_{3}O_{4} + 4 C 3 Fe + 4 CO
The trick here is to find the maximum amount of iron which could be made from each reactant.
The lesser amount will then be the max possible:
C: (3 mol Fe/ 4 mol C)(24.00 g C/ 12.01 g C/mol C) = 1.499 mole
Fe_{3}O_{4}: (3 mol Fe/ mol Fe_{3}O_{4})(115.0 g Fe_{3}O_{4}/231.6 g Fe_{3}O_{4}/mol Fe_{3}O_{4}) = 1.490 mole
therefore Fe_{3}O_{4} limits, can only make 1.490 moles Fe.
Grams = (1.490 moles Fe)(55.85 g Fe/mol Fe) = 83.217 g Fe = 83.22 g Fe
What is the maximum amount (moles) of hydrogen gas which may be produced by reacting 0.50 g of Zinc with 0.800 mole hydrogen ion? Show work!
Another frequent question arising in chemical processes is the percent yield. This deals with the question of how effective was a given process in producing a product. Its an important consideration because chemical reactions rarely go completley to products. The maximum possible yield for a reaction is known as the Theoretical Yield.
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© R A Paselk
Last modified 11 February 2013