Question

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)?

Answer 1

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_31H_64 + 47O_2 -> 31CO_2 + 32H_2O`

Work out the moles for this alkane.

`(0.72g)/(436)`= 0.00165 moles

The mole ratio of the alkane to `CO_2` is 1:31 so multiply the moles of the alkane by 31 to get the number of moles for `CO_2`.

`0.00165*31` =0.0511 moles

Multiply the moles of `CO_2` by `24dm^3` and then by 1000 to get it in `cm^3`.

`1000(0.0511*24) = 1266.4cm^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)