TBR General Chemistry; Section 1; Example 1.30

[Abdominis]

The question asks:

How many grams of water are formed when 25.0 grams of pentane (C5H12) reacts with oxygen?

I understand the solution to the question. However, the balanced equation has to be written out before a solution can be determined. How do I figure out what the balanced reaction is? I know how to balance a reaction once the reactants and products are written out in equation form...but how do I move from the words in the question above to the reaction?

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[boaz]

Do you know what the reactants and products are?

 

[Abdominis]

I'm guessing the reactants are pentane and oxygen and the product is water.

 

[boaz]

I'm guessing the reactants are pentane and oxygen and the product is water.

Where did the carbons (from pentane) go?

 

[Abdominis]

I wondered the exact same thing but there is nothing more to the question than what I have already posted above.

 

[boaz]

Did you learn about combustion reactions in gen chem?

 

[demayette]

I'm guessing the reactants are pentane and oxygen and the product is water.

Product is water and carbon dioxide. Then the problem is simple

 

[PiBond]

C5H12 + 8O2 --> 6H20 + 5CO2

then some dimensional analysis will do the trick

 

[Abdominis]

Ooooh, so water always a product in combustion reactions??

 

[PiBond]

Ooooh, so water always a product in combustion reactions??

not always, but on the MCAT you'll usually see them with organic molecules (C, H, O) which do yield water and carbon dioxide