[Script Info]
Title: 
[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:08.60,0:00:13.79,Default,,0000,0000,0000,,So you just strained a muscle\Nand the inflammation is unbearable.
Dialogue: 0,0:00:13.79,0:00:16.81,Default,,0000,0000,0000,,You wish you had something \Nice cold to dull the pain,
Dialogue: 0,0:00:16.81,0:00:21.30,Default,,0000,0000,0000,,but to use an icepack, you would have had\Nto put it in the freezer hours ago.
Dialogue: 0,0:00:21.30,0:00:23.42,Default,,0000,0000,0000,,Fortunately, there's another option.
Dialogue: 0,0:00:23.42,0:00:28.06,Default,,0000,0000,0000,,A cold pack can be left at room temperature\Nuntil the moment you need it,
Dialogue: 0,0:00:28.06,0:00:33.83,Default,,0000,0000,0000,,then, just snap it as instructed\Nand within seconds you'll feel the chill.
Dialogue: 0,0:00:33.83,0:00:37.14,Default,,0000,0000,0000,,But how can something go from \Nroom temperature to near freezing
Dialogue: 0,0:00:37.14,0:00:38.93,Default,,0000,0000,0000,,in such a short time?
Dialogue: 0,0:00:38.93,0:00:41.43,Default,,0000,0000,0000,,The answer lies in chemistry.
Dialogue: 0,0:00:41.43,0:00:44.40,Default,,0000,0000,0000,,Your cold pack contains water\Nand a solid compound,
Dialogue: 0,0:00:44.40,0:00:49.66,Default,,0000,0000,0000,,usually ammonium nitrate, in different\Ncompartments separated by a barrier.
Dialogue: 0,0:00:49.66,0:00:52.59,Default,,0000,0000,0000,,When the barrier is broken,\Nthe solid dissolves
Dialogue: 0,0:00:52.59,0:00:55.64,Default,,0000,0000,0000,,casuing what's known as an \Nendothermic reaction,
Dialogue: 0,0:00:55.64,0:00:58.52,Default,,0000,0000,0000,,one that absorbs heat from its surroundings.
Dialogue: 0,0:00:58.52,0:01:00.60,Default,,0000,0000,0000,,To understand how this works,
Dialogue: 0,0:01:00.60,0:01:04.54,Default,,0000,0000,0000,,we need to look at the two driving\Nforces behind chemical processes:
Dialogue: 0,0:01:04.54,0:01:07.19,Default,,0000,0000,0000,,energetics and entropy.
Dialogue: 0,0:01:07.19,0:01:13.03,Default,,0000,0000,0000,,These determine whether a change occurs in\Na system and how energy flows if it does.
Dialogue: 0,0:01:13.03,0:01:17.38,Default,,0000,0000,0000,,In chemistry, energetics deals with\Nthe attractive and repulsive forces
Dialogue: 0,0:01:17.38,0:01:20.32,Default,,0000,0000,0000,,between particles at the molecular level.
Dialogue: 0,0:01:20.32,0:01:26.18,Default,,0000,0000,0000,,This scale is so small, that there are\Nmore water molecules in a single glass
Dialogue: 0,0:01:26.18,0:01:29.45,Default,,0000,0000,0000,,than there are known stars in the universe.
Dialogue: 0,0:01:29.45,0:01:31.53,Default,,0000,0000,0000,,And all of these trillions \Nof molecules are
Dialogue: 0,0:01:31.53,0:01:36.18,Default,,0000,0000,0000,,constantly moving, vibrating \Nand rotating at different rates.
Dialogue: 0,0:01:36.18,0:01:39.78,Default,,0000,0000,0000,,We can think of temperature as\Na measurement of the average motion,
Dialogue: 0,0:01:39.78,0:01:42.80,Default,,0000,0000,0000,,or kinetic energy, of all these particles,
Dialogue: 0,0:01:42.80,0:01:46.91,Default,,0000,0000,0000,,with an increase in movement\Nmeaning an increase in temperature,
Dialogue: 0,0:01:46.91,0:01:48.73,Default,,0000,0000,0000,,and vice versa.
Dialogue: 0,0:01:48.73,0:01:51.60,Default,,0000,0000,0000,,The flow of heat in any \Nchemical transformation
Dialogue: 0,0:01:51.60,0:01:54.84,Default,,0000,0000,0000,,depends on the relative strength\Nof particle interactions
Dialogue: 0,0:01:54.84,0:01:57.91,Default,,0000,0000,0000,,in each of a substance's chemical states.
Dialogue: 0,0:01:57.91,0:02:00.76,Default,,0000,0000,0000,,When particles have a strong mutual\Nattractive force,
Dialogue: 0,0:02:00.76,0:02:03.84,Default,,0000,0000,0000,,they move rapidly towards one another,\Nuntil they get so close,
Dialogue: 0,0:02:03.84,0:02:07.61,Default,,0000,0000,0000,,that repuslive forces push them away.
Dialogue: 0,0:02:07.61,0:02:09.69,Default,,0000,0000,0000,,If the initial attraction was \Nstrong enough,
Dialogue: 0,0:02:09.69,0:02:13.29,Default,,0000,0000,0000,,the particles will keep vibrating back\Nand forth in this way.
Dialogue: 0,0:02:13.29,0:02:16.38,Default,,0000,0000,0000,,The stronger the attraction,\Nthe faster their movement,
Dialogue: 0,0:02:16.38,0:02:18.76,Default,,0000,0000,0000,,and since heat is essentially motion,
Dialogue: 0,0:02:18.76,0:02:22.46,Default,,0000,0000,0000,,when a substance changes to a state\Nin which these interactions are stronger,
Dialogue: 0,0:02:22.46,0:02:24.15,Default,,0000,0000,0000,,the system heats up.
Dialogue: 0,0:02:24.15,0:02:26.44,Default,,0000,0000,0000,,But our cold packs do the opposite,
Dialogue: 0,0:02:26.44,0:02:29.21,Default,,0000,0000,0000,,which means that when \Nthe solid dissolves in the water,
Dialogue: 0,0:02:29.21,0:02:33.34,Default,,0000,0000,0000,,the new interactions of solid particles \Nand water molecules with each other
Dialogue: 0,0:02:33.34,0:02:37.36,Default,,0000,0000,0000,,are weaker than the separate interactions\Nthat existed before.
Dialogue: 0,0:02:37.36,0:02:40.74,Default,,0000,0000,0000,,This makes both types of particles \Nslow down on average,
Dialogue: 0,0:02:40.74,0:02:42.49,Default,,0000,0000,0000,,cooling the whole solution.
Dialogue: 0,0:02:42.49,0:02:47.05,Default,,0000,0000,0000,,But why would a substance change to a\Nstate where the interactions were weaker?
Dialogue: 0,0:02:47.05,0:02:51.23,Default,,0000,0000,0000,,Wouldn't the stronger preexisting\Ninteractions keep the solid from dissolving?
Dialogue: 0,0:02:51.23,0:02:53.38,Default,,0000,0000,0000,,This is where entropy comes in.
Dialogue: 0,0:02:53.38,0:02:56.27,Default,,0000,0000,0000,,Entropy basically describes \Nhow objects and energy
Dialogue: 0,0:02:56.27,0:02:59.82,Default,,0000,0000,0000,,are distributed based on random motion.
Dialogue: 0,0:02:59.82,0:03:03.54,Default,,0000,0000,0000,,If you think of the air in a room, there\Nthere are many different possible arrangements
Dialogue: 0,0:03:03.54,0:03:05.90,Default,,0000,0000,0000,,for the trillions of particles \Nthat compose it.
Dialogue: 0,0:03:05.90,0:03:09.32,Default,,0000,0000,0000,,Some of these will have all \Nthe oxygen molecules in one area,
Dialogue: 0,0:03:09.32,0:03:11.90,Default,,0000,0000,0000,,and all the nitrogen molecules in another.
Dialogue: 0,0:03:11.90,0:03:14.51,Default,,0000,0000,0000,,But far more will have them \Nmixed together,
Dialogue: 0,0:03:14.51,0:03:17.70,Default,,0000,0000,0000,,which is why air is always\Nfound in this state.
Dialogue: 0,0:03:17.70,0:03:20.98,Default,,0000,0000,0000,,Now, if there are strong\Nattractive forces between particles,
Dialogue: 0,0:03:20.98,0:03:24.21,Default,,0000,0000,0000,,the probability of some configurations\Ncan change
Dialogue: 0,0:03:24.21,0:03:28.29,Default,,0000,0000,0000,,even to the point where the odds\Ndon't favor certain substances mixing.
Dialogue: 0,0:03:28.29,0:03:31.25,Default,,0000,0000,0000,,Oil and water not mixing is an example.
Dialogue: 0,0:03:31.25,0:03:35.20,Default,,0000,0000,0000,,But in the case of the ammonium nitrate,\Nor other substance in your cold pack,
Dialogue: 0,0:03:35.20,0:03:38.62,Default,,0000,0000,0000,,the attractive forces are not \Nstrong enough to change the odds,
Dialogue: 0,0:03:38.62,0:03:42.62,Default,,0000,0000,0000,,and random motion makes the particles\Ncomposing the solid separate
Dialogue: 0,0:03:42.62,0:03:47.31,Default,,0000,0000,0000,,by dissolving into the water\Nand never returning to their solid state.
Dialogue: 0,0:03:47.31,0:03:50.90,Default,,0000,0000,0000,,To put it simply, your cold pack gets \Ncold because random motion
Dialogue: 0,0:03:50.90,0:03:55.47,Default,,0000,0000,0000,,creates more configurations where \Nthe solid and water mix together
Dialogue: 0,0:03:55.47,0:03:59.22,Default,,0000,0000,0000,,and all of these have even weaker\Nparticle interaction,
Dialogue: 0,0:03:59.22,0:04:00.70,Default,,0000,0000,0000,,less overall particle movement
Dialogue: 0,0:04:00.70,0:04:05.19,Default,,0000,0000,0000,,and less heat than there was \Ninside the unused pack.
Dialogue: 0,0:04:05.19,0:04:08.12,Default,,0000,0000,0000,,So while the disorder that can result\Nfrom entropy
Dialogue: 0,0:04:08.12,0:04:10.51,Default,,0000,0000,0000,,may have caused your injury\Nin the first place,
Dialogue: 0,0:04:10.51,0:04:14.95,Default,,0000,0000,0000,,its also responsible for that\Ncomforting cold that soothes your pain.