Okay . . . this is not for a class because I don’t take chemistry. But a friend of mine posed this question to me:
If you were to take a frozen microwave popcorn bag and a room-temp microwave popcorn bag, which would pop first?
I say the frozen one would because of the whole heat differential rule in chemistry, but I can’t remember the name. All I know is I read about it in an article of Cecil’s about beer and the freezer. Anyone care to voice an opinion either way or name the law?
Thanks.
I read the column you referred to:
http://www.straightdope.com/classics/a1_118b.html
and I don’t think it applies since we’re talking about microwaves, and not putting the bag in the oven.
Microwaves cook differently, and I’m really not too sure whether the mentioned Fourier’s rule would apply…
Microwave ovens heat popcorn kernels by radiation, not by heat conduction. Since microwaves impart a fixed number of Watts of energy on the item in the microwave (wattage dependent upon the power level you choose and your particular model of microwave), it will take longer to pop a frozen kernel than a room-temperature one.
Even if you weren’t heating these things up in the microwave but were heating them by conduction (i.e. Fourier’s Law applies), the frozen bag still would not pop sooner. This situation is essentially different from the ‘beer cooling’ scenario covered by Cecil, in that the two different objects are both required to come to some greater temperature.
Look at it this way – in order to heat the frozen popcorn to pop temperature, it must first be heated to room temperature. Of course the first bag is already at room temperature, so it doesn’t require that time. Hence it pops sooner. The heater of course can’t tell the difference between a room temp. popcorn bag that was at 0 degrees a minute ago, and one that’s been at room temp. for 5 hours[sup]*[/sup].
So what about the faster heat transfer due to differential thing? That does indeed come in to play. It would simply mean, though, that to heat the frozen bag up by 20 degrees takes less time than to heat the room temp bag up by 20 degrees. The frozen bag, once it reaches room temp, will still take the same amount of time that the (possibly already popped) room temp bag did.
This isn’t true with the ‘chilling’ scenario, since the refrigerator and the freezer are treated as infinite heat sinks that stay at constant temperature. We aren’t heating them up, we’re transferring heat out of two cans at the same temperature.
hope that helps.
What’s up with the subject line?
[sup]*[/sup]One could argue that the frozen bag doesn’t reach room temp. uniformly, and thus is slightly different, but still, it won’t pop any faster.
What’s up with the subject line is that I was trying to think of an interesting title that would interest people. Evidently I didn’t do a very good job of it.
Thanks for your help, guys (and possibly girls).
Yeah, what panamajack said. A friend once tried to convince me that cold water would boil faster than warm water because cold water heats up faster. It took a long time to get the idea that a faster rate of change did not mean it would achieve the goal sooner.
From the subject line I was expecting a game where someone would post something like CH3-CH=CH-OH and the next person would name it (propenol?) and suggest the next.
But then I guess that wouldn’t be in General Questions, would it?
That would be either in #straightdope or MPSIMS. Very few people would play.
Sadly, I’m among those.
Actually, I think it did interest people, so in that sense it served its purpose. I have no problem with subject lines like that … didn’t mean to sound mean with my question, I was just curious. (I actually was thinking along the lines of obfusciatrist and was sad because I’d probably only be able to watch and not play.)
At least the subject of chemistry was involved and it wasn’t something like “This is A General Question”.