Question

My science teacher took a tin can with 2 holes in it, 1 on the top in the middle of the lid and one on the side near the bottom. He filled it with methane and then lit the methane from the top hole. It burned for a while and the flame slowly degraded. Finally, the flame was filling the top whole and BOOM! the lid of the can (with the hole) popped off. Can someone PLEASE explain how this happened? It doesn't make any sense.

Answer 1

Could the flame be dense enough to plug the top hole?

Answer 2

i think when he lit methane from the top hole ,combustion took place, getting oxygen supply from the bottom hole.due to combustion the product gases of this reaction increased the pressure inside the can and lid opened with a pop...:)

Answer 3

That's interesting. Here's my hypothesis:

Near the top of the can, the following combustion reaction was taking place:
\[2{\rm CH}_4(g) + 3{\rm O}_2(g) \rightarrow 2 {\rm CO}_2(g) + 4{\rm H}_2{\rm O}(g)\]
Now, even if we assume oxygen is already mixed with the methane, this reaction produces 6 moles of gases for every 5 moles of gases it consumes. Each mole of gas occupies the same volume at a given pressure. So if this reaction consumes 50 cm^3 of methane and oxygen, it generates 60 cm^3 of carbon dioxide and water. CO2 is significantly heavier than air, and water vapor barely heavier, so both products might well stay in the can instead of exiting the top.

Combined with the rise in temperature, this would cause the pressure in the can to rise, eventually popping the top off.

Is this correct? I don't know for sure. One would have to make some experimental tests to confirn the idea.

Answer 4

Both of you make a lot of sense. Thanks so much :D This certainly has helped for more research :)

Answer 5

@Carl_Pham your hypothesis is correct.the thing is when the volume of product gases inside the confined volume of the tin can increases it generates a considerable amount of pressure.Even though both co2 & vapors are heavier than air but still the pressure generated would be enough to pop the lid (weakest part in whole can) off ..:)

Answer 6

So do you think the hole in the bottom really effects anything? That's the part that is still confusing me.

Answer 7

yes it does..see for combustion u need oxygen supply..from top hole you get methane(fuel)
,and from bottom you get oxygen..

Answer 8

Can you think of anything this relates to in the real world? I'm still having trouble understanding this.

Answer 9

umm...have you seen a gas stove lately??
if u see beneath it u will find a hole inside the fuel input pipe just after the control knob.that hole is indeed for the oxygen input.

Answer 10

That makes sense. Also I found that internal combustion engines work the same way.

Answer 11

yes ,you are totally right:)