Help with Chemistry homework problem

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C3H8(g)    +   O2(g) ======>    CO2(g)   +    H2O(g),

where DH = –531 kcal.  If 6.70 × 104 kcal of energy is released in the reaction, how many grams of oxygen were consumed?

Nov 24th, 2014

The definition DH of  is the enthalpy change that occurs in a system when one mole of matter is transformed by a chemical reaction.

The above equation should be written as for complete combustion:

C3H8(g)   + 5 O2(g) ======>  3 CO2(g)   + 4 H2O(g)

Since for 1mol C3H8, DH=-531 kcal

-6.70 x 10^4 / -531=126 mol 

Therefore 126mol C3H8 were consumes, and accordingly 126x5 mol O2 were consumed.

While the molecular weight of O2 is 32 g/mol

126x5mol x 32g/mol=630x32=2.02x10^4 g

So 2.02x10^4 g oxygen were consumed.


Nov 24th, 2014

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