Question

Question #60074

Answer 1

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")))`