Heat Exchange

WEBVTT
Kind: captions
Language: en

00:00:06.140
hi it's mr. Andersen and this is
00:00:08.270 00:00:08.280 chemistry essentials video 47 it's on
00:00:10.459 00:00:10.469 heat exchange if I were to say don't
00:00:12.230 00:00:12.240 touch this iron right here in the middle
00:00:13.879 00:00:13.889 it's hot what does that mean well we
00:00:16.160 00:00:16.170 know that it has a higher temperature
00:00:17.420 00:00:17.430 and therefore it has a higher amount of
00:00:19.580 00:00:19.590 average kinetic energy and if you were
00:00:21.470 00:00:21.480 to touch it a lot of that energy is
00:00:23.060 00:00:23.070 going to be transferred to your hand and
00:00:25.070 00:00:25.080 that's going to produce quite a bit of
00:00:26.660 00:00:26.670 pain and so if we ever have a warmer
00:00:28.400 00:00:28.410 body and a colder body the warmer body
00:00:30.740 00:00:30.750 is going to have more kinetic energy and
00:00:32.630 00:00:32.640 again that energy is in the molecular
00:00:34.340 00:00:34.350 motion or those molecules moving around
00:00:36.319 00:00:36.329 and we're going to have more energy in
00:00:38.330 00:00:38.340 that than the colder body and so a good
00:00:40.340 00:00:40.350 way to represent that and I'll use this
00:00:42.350 00:00:42.360 model over the next few videos is just
00:00:44.299 00:00:44.309 using these little cubes that represent
00:00:46.369 00:00:46.379 the amount of energy in this case that's
00:00:48.110 00:00:48.120 going to be thermal energy and so if I
00:00:50.299 00:00:50.309 were to put those two objects in contact
00:00:52.700 00:00:52.710 with one another that energy is going to
00:00:55.040 00:00:55.050 be transferred in other words energy is
00:00:57.020 00:00:57.030 moving from that first object to that
00:00:58.970 00:00:58.980 second object and we call that transfer
00:01:01.520 00:01:01.530 heat and so what we're really doing is
00:01:03.590 00:01:03.600 transferring energy as thermal energy or
00:01:06.080 00:01:06.090 heat now heat if you were to look up
00:01:07.880 00:01:07.890 heat on the periodic table you're simply
00:01:10.070 00:01:10.080 not going to find it there because it's
00:01:11.390 00:01:11.400 not a substance it's not a thing it's
00:01:13.310 00:01:13.320 just the transfer of energy and so a
00:01:15.320 00:01:15.330 good way to think about that and this
00:01:16.910 00:01:16.920 should be a sentence that should kind of
00:01:18.649 00:01:18.659 roll off your tongue
00:01:19.420 00:01:19.430 energy is being transferred as heat
00:01:21.590 00:01:21.600 that's really what's going on and so
00:01:24.140 00:01:24.150 when we're looking at energy being
00:01:26.179 00:01:26.189 transferred as heat it's going to vary
00:01:27.920 00:01:27.930 depending on the substance that we're
00:01:29.630 00:01:29.640 dealing with in other words metals are
00:01:32.480 00:01:32.490 going to transfer energy through heat
00:01:34.069 00:01:34.079 more readily than things like wood or
00:01:36.289 00:01:36.299 brick so let's look at this Paet
00:01:38.210 00:01:38.220 simulation so I've got iron i've got
00:01:40.580 00:01:40.590 brick and then i've got water and so we
00:01:43.190 00:01:43.200 can assume that we have the same amount
00:01:44.840 00:01:44.850 of each of these and if i were to put
00:01:46.670 00:01:46.680 the water on top of a heating device and
00:01:49.429 00:01:49.439 the iron on top of a heating device and
00:01:51.319 00:01:51.329 I were to just increase the amount of of
00:01:52.990 00:01:53.000 energy what I'm going to see is an
00:01:55.399 00:01:55.409 increase in temperature well what's
00:01:56.749 00:01:56.759 really going on is that we're speeding
00:01:58.550 00:01:58.560 up those molecules that's speeding up
00:02:00.230 00:02:00.240 the molecules of the thermometer it's
00:02:01.700 00:02:01.710 spreading a power likewise when we cool
00:02:03.679 00:02:03.689 it down what we're doing is we're
00:02:05.539 00:02:05.549 cooling down those molecules cooling
00:02:07.490 00:02:07.500 down the molecules of the thermometer
00:02:09.050 00:02:09.060 and therefore it's going down but we
00:02:11.300 00:02:11.310 really don't see that energy transfer is
00:02:13.250 00:02:13.260 he
00:02:13.600 00:02:13.610 and so now what we're going to do is
00:02:15.040 00:02:15.050 we're going to click on the energy
00:02:16.330 00:02:16.340 symbols button and now we're actually
00:02:18.370 00:02:18.380 going to see that energy inside those
00:02:20.410 00:02:20.420 molecules now as I'm heating it up
00:02:22.330 00:02:22.340 what's really happening is I'm adding
00:02:24.370 00:02:24.380 energy I'm adding energy to that iron
00:02:27.010 00:02:27.020 now you can see that some of it is being
00:02:28.840 00:02:28.850 transferred out to the environment
00:02:30.460 00:02:30.470 through heat
00:02:31.090 00:02:31.100 likewise when I cool it down what I'm
00:02:33.160 00:02:33.170 doing is I'm actually transferring that
00:02:34.870 00:02:34.880 energy as heat into the ice cubes so
00:02:36.940 00:02:36.950 there have lower kinetic energy what
00:02:39.610 00:02:39.620 happens if I take that iron and I just
00:02:41.200 00:02:41.210 throw it into the water you can see that
00:02:42.850 00:02:42.860 since it's hotter it's transferring some
00:02:44.680 00:02:44.690 of that energy as heat as well to the
00:02:46.960 00:02:46.970 surroundings until it eventually reaches
00:02:48.790 00:02:48.800 what we call equilibrium and so if you
00:02:51.310 00:02:51.320 ever have a warmer and a colder body
00:02:53.230 00:02:53.240 that warmer body is going to have a
00:02:55.000 00:02:55.010 higher amount of average kinetic energy
00:02:57.010 00:02:57.020 and remember the Maxwell Boltzmann
00:02:58.449 00:02:58.459 distribution shows us how that works if
00:03:00.940 00:03:00.950 we were to look at it this would be the
00:03:02.050 00:03:02.060 cold body and this would be the warm
00:03:03.699 00:03:03.709 body now in each of those bodies they're
00:03:05.410 00:03:05.420 going to have low energy particles and
00:03:07.630 00:03:07.640 really high energy particles but in the
00:03:09.520 00:03:09.530 warmer body that average kinetic energy
00:03:11.650 00:03:11.660 is going to be greater and so if we ever
00:03:13.690 00:03:13.700 put them in contact with another there's
00:03:15.699 00:03:15.709 going to be a lot of collisions between
00:03:17.290 00:03:17.300 these molecules and as they collide
00:03:19.000 00:03:19.010 they're transferring some of that
00:03:20.500 00:03:20.510 kinetic energy and so what we're really
00:03:22.330 00:03:22.340 doing is we're transferring energy from
00:03:24.190 00:03:24.200 the warmer object to the colder object
00:03:25.990 00:03:26.000 through heat until they eventually reach
00:03:28.600 00:03:28.610 what we call thermal equilibrium in
00:03:30.850 00:03:30.860 other words it's the same average
00:03:31.990 00:03:32.000 kinetic energy on both sides and that
00:03:34.180 00:03:34.190 picture I showed you of iron at the
00:03:35.560 00:03:35.570 beginning eventually what's going to
00:03:37.150 00:03:37.160 happen is all of that iron is going to
00:03:38.949 00:03:38.959 have the same amount of kinetic energy
00:03:40.960 00:03:40.970 because we've transferred that energy
00:03:42.729 00:03:42.739 out now it's not the same for every
00:03:44.740 00:03:44.750 substance and so we use a term called
00:03:47.410 00:03:47.420 specific heat capacity to measure that
00:03:49.300 00:03:49.310 and so right here you could imagine we
00:03:51.130 00:03:51.140 have a kilogram of gold a kilogram of
00:03:53.710 00:03:53.720 aluminum and a kilogram of water and
00:03:56.320 00:03:56.330 let's say that they're all in a
00:03:58.360 00:03:58.370 container and so if you look at it
00:04:00.250 00:04:00.260 they're going to have different amounts
00:04:01.360 00:04:01.370 of specific heat capacity if we look at
00:04:03.280 00:04:03.290 the units that's joules which is a way
00:04:05.259 00:04:05.269 that we measure energy per gram and then
00:04:07.780 00:04:07.790 Kelvin or degree Kelvin and so if you
00:04:10.180 00:04:10.190 have something that has low specific
00:04:12.070 00:04:12.080 heat capacity that means it's going to
00:04:13.780 00:04:13.790 be chained the amount of energy it has
00:04:15.940 00:04:15.950 is going to change more readily than
00:04:17.409 00:04:17.419 something that has a higher heat
00:04:19.140 00:04:19.150 specific heat capacity so let's add a
00:04:21.729 00:04:21.739 little bit of heat to this and watch
00:04:23.230 00:04:23.240 what happens to the thermometers
00:04:25.350 00:04:25.360 and so the goal the aluminum are heating
00:04:28.170 00:04:28.180 up more readily than the water now the
00:04:30.450 00:04:30.460 energy is going to be the same it's just
00:04:32.700 00:04:32.710 that the water has a higher specific
00:04:33.869 00:04:33.879 heat capacity and so it's able to absorb
00:04:36.839 00:04:36.849 more energy before it starts to change
00:04:38.670 00:04:38.680 its temperature and so did you learn to
00:04:41.189 00:04:41.199 explain how heat exchange is due to
00:04:43.110 00:04:43.120 kinetic energy transfer due to molecular
00:04:45.420 00:04:45.430 motions if you did you learned what I
00:04:48.270 00:04:48.280 wanted you to and I hope that was
00:04:49.589 00:04:49.599 helpful
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