There is nothing like the smell of BBQ in the summertime. Many people use propan

Question

There is nothing like the smell of BBQ in the summertime. Many people use propane gas barbeques to cook the perfect steak. Here is the reaction that is occuring while the steak sizzles on the grill:

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

The balanced reaction has a -2217 kJ. If a steak must absorb 7.2 * 10^-4 kJ to reach a perfect medium rare and only 15% of the heat produced by the barbeque is actually absorbed by the steak, what mass of H2O is emitted into the atmosphere when the steak is cooked?

Explanation / Answer

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

Heat produced = 100/15 x heat absorbed by steak

= 100/15 x 7.2 x 10^(-4)

= 0.0048 kJ


Moles of H2O produced = heat produced/2217 x 4

= 0.0048/2217 x 4 = 8.6604 x 10^(-6) mol


Mass of H2O produced = moles x molar mass of H2O

= 8.6604 x 10^(-6) x 18.02

= 1.56 x 10^(-4) g = 1.6 x 10^(-4) g

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