[999iscool]

If we initially lighted a candle, and then put a jar over it, what can we say about the fire? What kind of observations can we make?


Well the observations are quite obvious. The flame is put off soon or later, and fogs and smoke will form.

So " the number of O2 molecules used should equal to the number of carbon atoms used; the total energy and mass of the system should be conserved inside."  Is this true?

This brings up two more sub questions:
1. how can we make sure there is no loss of heat? or how do we calculate the loss of heat because the jar is not insulated-proof?
2. what are other chemical products produced during the burning process?

Precisely, we do need to measure the inside quantitatively in order to verify our claims that heat is generated and oxygen is consumed during burning and that carbon dioxide are also produced.

Thanks.

[DevaDevil]

So " the number of O2 molecules used should equal to the number of carbon atoms used

not true, you formulate an explanation as to why... (not giving everything away)

the total energy and mass of the system should be conserved inside." 

true of course

[999iscool]

Hi DevaDevil,

Thanks for your response.

I think I did skip the details of combustion. Sorry I almost have forgotten my basic chemistry here.

1. Products in combustion of candle-fire experiment are H2O, CO2, and heat if I am also correct.
2. With the volume of the gas inside remains constant (because it is contained by the glass jar), increasing the temperature should increase the pressure by the ideal gas law (gaining kinetic energy). We can certainly measure the changes of pressure with a sensory detector.
3. To verify whether oxygen is an reactant (the left side of the equation), we will need to measure the amount of H2O and CO2 produced, and the numbers should match our calculated values when we balance out the chemical equation.
4. An increase of temperature.

The equation should looks like this

 x *< candle compound> + y * O2 =>  a * H2O + b * CO2 + thermal heat

5. The bottom line is:  mass and energy should be conserved.


PS:  If there is any misused terminology (chemical equation, compound, etc) please do correct me!  Thanks

[Borek]

the total energy and mass of the system should be conserved inside." 

true of course

Mass is conserved inside, but heat escapes.