# Mass of candle 0.72 g before burning. What is the mass of the products of this reaction? Would that be the same thing as weighing the candle again (the mass is 0.27 g after burning)?

May 5, 2017

Refer to explanation

#### Explanation:

Reweighing the candle before and after burning just shows how much fuel was burnt.
Typical candle wax is an alkane such as hentriacontane, so write a chemical formula for the combustion of this alkane.

${C}_{31} {H}_{64} + 47 {O}_{2} \to 31 C {O}_{2} + 32 {H}_{2} O$

Work out the moles for this alkane.

$\frac{0.72 g}{436}$= 0.00165 moles

The mole ratio of the alkane to $C {O}_{2}$ is 1:31 so multiply the moles of the alkane by 31 to get the number of moles for $C {O}_{2}$.

$0.00165 \cdot 31$ =0.0511 moles

Multiply the moles of $C {O}_{2}$ by $24 {\mathrm{dm}}^{3}$ and then by 1000 to get it in $c {m}^{3}$.

$1000 \left(0.0511 \cdot 24\right) = 1266.4 c {m}^{3}$

Hence for water, do 0.0511 moles times by its formula mass, 18.

#0.0511*18= 0.92g of water.

(I may have overcomplicated it a bit)