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Course: High school chemistry > Unit 6
Lesson 2: Specific heat capacitySpecific heat capacity
Heat capacity is a property that describes how much energy is needed to change the temperature of a material. Objects with a high specific heat capacity require a greater change in energy to change their temperature and vice versa for objects with a low specific heat capacity. Measured in units of Joules per Kelvin kilogram, the specific heat capacity of material can be used to find the change in thermal energy when an object undergoes a temperature change. Created by Khan Academy.
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- Will we get more short videos that explain a lot? Those help me a lot.(12 votes)
- at1:50, what is the difference between specific heat capacity and heat capacity?(4 votes)
- Spesific heat capacity can measure for per mass. But heat capacity is depended on mass, you can calculate heat capacity of an object using its mass. But if you want to calculate spesific heat capacity of an object, you calculate it per mass, so it isn't depend on mass. I thing the difference between these terms are this.(6 votes)
- Hi!! What happens if it's stated that the mass is the same between two objects (need to find the heat capacity of one).(3 votes)
- how do we know the specific heat capacity like she stated around4:00?(1 vote)
- Here is what I found in answer to your question!
Specific Heat Capacity:
Specific heat capacity (also known as specific heat) focuses on a unit of mass of a substance.
It quantifies how effectively a material can absorb and store thermal energy.
Specifically, the specific heat capacity is the amount of heat energy needed to raise the temperature of one gram of a substance by one degree Celsius (or one Kelvin).
The units for specific heat capacity are either J/(g°C) or equivalently J/(g·K).
Measurement Methods:
Specific heat capacity can be determined experimentally using various methods:
Constant Pressure (cₚ): Measurements are performed at constant pressure. This value includes heat energy used to do work (such as expansion) against the constant pressure as the temperature increases.
Constant Volume (cᵥ): Measurements are performed at constant volume. Values obtained under constant volume are typically smaller because they exclude work done against pressure changes.
Laser Flash Technique (LFA): Among other methods, LFA can determine specific heat capacity. LFA involves rapid heating of a sample and measuring the resulting temperature rise.
Hope this helps!
Happy Learning!
Angelina(1 vote)
- I've seen things like c=4186 J kg^-1 K^-1 but at
I am seeing 4184. Why are numbers changing like this based on where I see it?3:25(1 vote)- Here is what I found to answer your question!
Specific Heat Capacity :
Specific heat capacity represents how much heat energy is needed to raise the temperature of a substance by one degree Celsius (or one Kelvin) per unit mass.
It’s like a unique fingerprint for each material, revealing how well it “holds onto” or “releases” heat.
The Numbers Game:
Water (H₂O):
The specific heat capacity of water is approximately 4184 J/(kg·K).
This value is commonly used in calculations involving water because it’s close to the specific heat capacity of liquid water at room temperature.
The 4186 Mystery:
You mentioned seeing 4186 J/(kg·K). Fear not! It’s just a different approximation.
Some sources use the value 4186 J/(kg·K) for water.
It’s a rounded-off value that’s still quite accurate.
The difference between 4184 and 4186 is minimal, especially for everyday calculations.
Precision and Context:
The specific heat capacity can vary slightly based on factors like temperature, pressure, and impurities.
Scientists and engineers often use more precise values for specific applications (e.g., thermodynamics, engineering design).
For most practical purposes, either value works well.
Why the Variation?
Different textbooks, databases, and scientific references might use slightly different values due to rounding or variations in experimental measurements.
The 4184 value is based on extensive experimental data, while 4186 is a convenient approximation.
The key is to use the value consistent with the context of your problem.
Takeaway:
Whether you choose 4184 or 4186, you’re in the right ballpark! Just remember that specific heat capacities can be quirky, but they’re essential for understanding heat transfer and thermodynamics.
Hope this helps!
Happy Learning!
Angelina(1 vote)
Video transcript
- [Instructor] Hello everyones. Today we are going to be
talking about heat capacity, also known as thermal capacity. Now this is just the
amount of heat required to change the temperature of a material. So given this definition, what units would you expect
heat capacity to have? Heat is a form of energy and we're describing how
much of that is needed to change the temperature, so the units for heat capacity
are energy per temperature, in SI would be Joules per Kelvin. Now, remember, in SI we
use Kelvin for temperature, which is the same in magnitude as Celsius. So a difference of 1 degree Celsius is equal to a difference of 1 Kelvin, however, Kelvin does not
have any negative numbers, and so 0 Kelvin is as low as you can get. Now, you probably already have
an intuitive understanding of heat capacity even if you haven't heard it phrased exactly like this before. Imagine you have two pots of
water over the same burner, but one of the pots is full of water and the other is only about half full. You would probably expect
the one with less water in it to boil faster, and this is actually because
of the heat capacity. The pot with the less water in it has a lower heat capacity. And this is because one of the things that heat capacity depends on is the mass of the object or system. Less water is less mass
xis a lower heat capacity. The other thing that the
heat capacity depends on is the material. This is also something
you are probably already intuitively familiar with. Imagine you go to a barbecue on a hot day and there are two folding chairs left open for you to choose between. One is made of metal,
the other of plastic, and they've both been
sitting out in the sun. You'd probably choose the plastic one to save yourself some discomfort. The reason that the metal
chair would be hotter despite both chairs having
been sitting out in the sun is because metal and plastic
are different materials and have different heat capacities. So we know that the heat
capacity of an object or system depends on both the mass and
the material it is made of. We can actually combine these then into something called
specific heat capacity. Now the specific heat capacity is just the heat capacity per mass. This means that the specific heat capacity is independent of the mass of the system because we're measuring it per mass. Therefore, this is constant
for a given material. This means it will take
the same amount of energy to raise the temperature of 1 kilogram of any given material, but then for a different material, it will take a different amount of energy. Given this, what do you expect the units of specific heat capacity to be? Well, just like heat capacity, we have an energy per temperature, but now we also have a per mass. In SI this is going to be
Joules per Kelvin per kilogram. This means that the heat capacity and the specific heat
capacity are related by mass. so, if you have a specific heat capacity and you want to get
the total heat capacity for the object or system, then you need to multiply by
the object or system's mass. Conversely, if you have the
heat capacity and the mass and you want to figure out what the heat capacity of a material is, you can divide the heat
capacity by the mass. However, because specific heat capacity is a constant property
of a given material, we can usually just go ahead
and look up what that value is because scientists have already measured the specific heat capacities
of lots of materials. Let's consider the water in
those pots we talked about. Pure liquid water has a
specific heat capacity of 4,184 Joules per Kelvin per kilogram, but different materials have different specific heat capacities. So let's think back to our
chairs at a barbecue example and how the metal chair is
hotter than the plastic chair. Now metal folding chairs are
typically made of aluminum, which has a specific heat capacity of 897 Joules per Kelvin per kilogram. Solid plastic, however, has a specific heat capacity of 1,670 Joules per Kelvin per kilogram. So you can see from the
specific heat capacities that since the sun is providing
the same amount of energy to both chairs, the temperature of the metal chair is getting much more increased because it needs less energy
to increase its temperature because it has a lower
specific heat capacity. Now that we see how the material
changes the heat capacity, let's talk a bit more about the mass and go back to our example of the pots. So in these pots, we
have pure liquid water, which we know now has a
specific heat capacity of 4,184 Joules per Kelvin per kilogram. Now the pots themselves
also have a heat capacity, but we're going to ignore
that to simplify the problem. If this pot has 2
kilograms of water in it, we can calculate how
much energy it will take to change the temperature of this water. Let's say that the initial
temperature of the water is about 300 Kelvin, which is approximately room temperature. And suppose we want to use this water to make some white tea, which has made best with water
that's at about 355 Kelvin. Based off our understanding
of heat capacity now, we can figure out how many
joules it is going to take to raise the water from
300 Kelvin to 355 Kelvin. We have the specific
heat capacity and a mass, and we know we can multiply those to get a total heat capacity. And we know that by definition, heat capacity is the energy
required per temperature, which means that if we
multiply the heat capacity by the change in temperature, we'll find out what
the energy required is. In fact, this relationship is an important thermodynamic equation. Lower case c is commonly used
for specific heat capacity and Q for heat. So this is exactly what
we've just worked out. The heat or energy required equals the specific heat
capacity times the mass, times the change in temperature. Let's go ahead and put our values in here. The mass, specific heat capacity, and the change in temperature. As always, we can use
our units to guide us. Specific heat capacity has a unit of Joules
per Kelvin per kilogram, we're multiplying mass that
has a unit of kilograms, so those kilograms will cancel out. We're also multiplying by
a change in temperature, which is measured Kelvin. And so that will also cancel out, leaving us just with
joules which is an energy, just like we want. In this case, if we
multiply this together, we would find that the energy required would be 460.24 kilojoules. Now, let's consider the other pot. If this pot has 1 kilogram of water, how would that change our calculation? Pause the video and think about what its
heat capacity would be. So because we still have the same material and therefore the same
specific heat capacity, the total heat capacity is
going to decrease by half because of the mass is half. And since we still want to
raise the water's temperature, the same amount, this means that the energy required is going to decrease by half as well, now requiring 230.12 kilojoules. So now we can see how the mass, as well as the material
affect heat capacity. Today we talked about heat capacity. We learned that it is the
amount of heat required to change the temperature of a material and that it is measured
in Joules per Kelvin, and that it depends on
both the mass of the system and the materials that
the system is made up. We did a couple of examples to help us quantify this
intuitive understanding we have of the world around us. And I encourage you to think about the ways
he capacity pops up in your everyday life. For example, why are some
things drier than other things when you unload the dishwasher?
Have a think about that. Thank you so much for joining us. I hope you learned a
little bit of something, and we'll see you again next time. Bye.