Question #60074

1 Answer
Dec 23, 2017

Answer:

The answer is (b).

Explanation:

The thermochemical equation given to you tells you that when #1# mole of propane undergoes combustion, #"2200 kJ"# are being given off.

You can tell that the heat is being given off and not absorbed because it was added on the products' side, which implies that it is a product of the reaction.

#"C"_ 3"H"_ (8(g)) + 5"O"_ (2(g)) -> 3"CO"_ (2(g)) + 4"H"_ 2"O"_ ((g)) + "2200 kJ"#

You also know that propane has a molar mass of #"44.1 g mol"^(-1)#, which means that #1# mole of propane has a mass of #"44.1 g"#.

This tells you that when #"44.1 g"# of propane undergo combustion, i.e. the equivalent of #1# mole, the reaction produces #"2200 kJ"# of heat.

You can thus say that when #"22.0 g"# of propane react, the reaction will produce

#22.0 color(red)(cancel(color(black)("g"))) * "2200 kJ"/(44.1color(red)(cancel(color(black)("g")))) = "1097.5 kJ"#

Write the answer in scientific notation and round it to three sig figs to get

#"heat given off by 22.0 g C"_3"H"_8 = color(darkgreen)(ul(color(black)(1.10 * 10^3color(white)(.)"kJ")))#