# Question 60074

Dec 23, 2017

#### Explanation:

The thermochemical equation given to you tells you that when $1$ mole of propane undergoes combustion, $\text{2200 kJ}$ 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.

$\text{C"_ 3"H"_ (8(g)) + 5"O"_ (2(g)) -> 3"CO"_ (2(g)) + 4"H"_ 2"O"_ ((g)) + "2200 kJ}$

You also know that propane has a molar mass of ${\text{44.1 g mol}}^{- 1}$, which means that $1$ mole of propane has a mass of $\text{44.1 g}$.

This tells you that when $\text{44.1 g}$ of propane undergo combustion, i.e. the equivalent of $1$ mole, the reaction produces $\text{2200 kJ}$ of heat.

You can thus say that when $\text{22.0 g}$ 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")))#