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Heat Capacity and Heat Transfer

by Jared Rovny
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    00:01 Now we're going to take a closer look at the phenomenon of heat transferring, how we can put more heat into systems or what happens when heat leaves systems as well.

    00:12 So as a quick, I'll review to make sure we're very familiar with these units.

    00:15 We talked about Q, the capital letter Q will represent heat.

    00:19 So everytime you see this letter Q, really be thinking in your mind about the heat transfer, this thermal energy going into or out of systems.

    00:26 And don't forget that we also introduced a new unit for this heat, one of which is joules, but this new one of which is calories, which is just a number of joules as 4.2 joules.

    00:36 We're now ready to go back to something that we had mentioned initially a little while ago, which was the heat capacity.

    00:43 And again, remember the heat capacity is trying to tell us how much energy we have to put into a system if we want the temperature to go up by a certain amount.

    00:53 So we see already right out the gate that we have a difference between the heat and the temperature.

    00:59 So in this heat capacity equation we have here, we have heat energy added which is in the numerator, and the temperature change of your system which is in the denominator.

    01:09 So again, the heat energy that you add, the heat and the temperature change of your system are going to be different quantities in a degree to which they're different is given to us by this heat capacity.

    01:21 We also discussed already and mentioned briefly the specific heat, which was how much energy was required per unit temperature per a given amount of mass.

    01:30 And so for a given problem, you have to be careful which one of these quantities you know whether you know the amount of joules per Kelvin, how much energy per temperature, or whether you know the amount of joules per Kelvin times mass, Whether that mass is in grams or otherwise.

    01:43 So be careful to watch out for those units.

    01:46 And again, look at the equations that we have here for the heat capacity and the specific heat capacity.

    01:51 We're now representing that heat that we are putting into our system by the letter Q, which is a capital letter Q.

    01:58 Note that you can always go between the heat capacity and the specific heat capacity simply by multiplying by the mass.

    02:06 So we have a simple relationship between these two.

    02:09 The heat added to a system for a given change of temperature is given by the heat capacity times that changes in temperature, again using the heat capacity in joules per Kelvin or is equal to the specific heat times the mass times the change in temperature.

    02:25 We're gonna specific heat will have unit of mass in the denominator so you can always be sure you're getting this right.

    02:31 You might have noticed by this point that unlike what we talked about before, we're now using a capital letter Q for the heat.

    02:37 So be aware that in different context, especially in a chemistry context, often the lower case letter q is used for heat instead of the capital letter Q, which is what we'll be using all throughout the rest of this thermodynamics discussion.

    02:51 There are few ways that heat can be transferred between objects, one of them is just conduction, and this is when two objects are right in contact with each other and the atoms or the molecules and one of them which are vibrating because of heat can be transferred directly to the atoms or molecules in the other system just directly by conduction by the impact or contact of those molecules or atoms.

    03:13 A different way we could transfer heat, would be to heat up a third object maybe the air using one system and then that air could transfer a flow from one system to the other in the process of convection.

    03:25 And so we could have some third thing as a mediary taking the heat from one system and then going and delivering the heat to a different system.

    03:32 So this is used often in for example, ovens if you want a convection oven to heat up your food, it's going to use elements or some sort of a heating process to heat up the air, and then cook the food using this process of convection by sending that hot air instead of by direct contact.

    03:47 Finally, there's one last way that we can transfer heat between systems which is using radiation.

    03:53 And this is exactly the radiation that we've already discussed in the past.

    03:56 It's photons, it's electromagnetic energy that's going from one system which has heat and leaving that system because of the motion of the molecules.

    04:04 That motion which we discussed especially in the context of the infrared radiation, the motion of those molecules sends phontons away from a hotter system and those photons can then impinge on and impact a colder system, transferring heat that way via the photons or via the radiation.


    About the Lecture

    The lecture Heat Capacity and Heat Transfer by Jared Rovny is from the course Thermodynamics and Thermochemistry.


    Included Quiz Questions

    1. Heat energy added / temperature changed
    2. Temperature changed / heat energy added
    3. Heat energy added - temperature changed
    4. Heat energy added x temperature changed
    5. Heat energy added + temperature changed
    1. The energy required per unit temperature for given amount of mass
    2. The energy required per unit temperature
    3. The temperature that is required for every energy unit
    4. The amount of mass consumed per unit temperature
    5. The mass required for every unit of temperature
    1. Conduction
    2. Convection
    3. Radiation
    4. Zonation
    5. Circumduction
    1. Conduction
    2. Convention
    3. Radiation
    4. Circumduction
    5. Zonation

    Author of lecture Heat Capacity and Heat Transfer

     Jared Rovny

    Jared Rovny


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