Specific Heat Capacity
Summary
TLDRToday's lesson focused on specific heat capacity within thermal physics for AQA A-Level. It explained how work can be done into a system's internal energy, defining specific heat capacity and measuring work done through internal energy changes. The lesson highlighted the first law of thermodynamics, detailing how heat transfer occurs from hotter to cooler substances and the role of radiation. The key formula \(\Delta Q = mc\Delta T\) was introduced, illustrating how to calculate the energy needed for a substance's temperature change. An example problem demonstrated calculating the energy required to heat water, emphasizing the importance of units and significant figures.
Takeaways
- 🔍 Specific heat capacity is a key concept in thermal physics, part of the AQA A Level Physics curriculum.
- 🔧 Work done on a system can increase or change the average kinetic or potential energy of a substance, affecting its internal energy and temperature.
- 🌡️ The first law of thermodynamics states that the change in internal energy is equal to the work done on the system.
- ↗️ An increase in kinetic energy store results in a rise in temperature, while a decrease leads to a fall.
- ♨️ Heat is transferred from hotter to cooler substances, and the rate of heat transfer is influenced by the temperature difference.
- 🌡️ The equation ΔQ = mcΔT links the work done, mass, specific heat capacity, and temperature change of a substance.
- 💧 The specific heat capacity of water is 4200 J/kg·K, which is a value often provided in exam questions.
- 🔢 The calculation of energy required to change the temperature of a substance involves the mass of the substance, its specific heat capacity, and the temperature change.
- ✅ It's crucial to use the correct units and significant figures when calculating and reporting results in physics.
- 🔙 The direction of work done is from high to low temperature, indicating an increase in internal energy when the temperature rises.
Q & A
What is specific heat capacity?
-Specific heat capacity is the amount of heat energy required to raise the temperature of one kilogram of a substance by one degree Celsius (or one Kelvin) without changing its state.
How does work relate to the internal energy of a system?
-Work done on a system is directly related to changing its internal energy, which can either increase or change the average kinetic or potential energy of the substance.
What is the first law of thermodynamics as mentioned in the script?
-The first law of thermodynamics, as mentioned in the script, states that the change in internal energy of a system is equal to the work done on the system.
Why does heat transfer occur?
-Heat transfer occurs because energy is transferred from particles with higher energy (hotter substances) to particles with lower energy (cooler substances), moving from higher temperatures to lower temperatures.
How does the potential energy store in a system relate to its internal energy?
-In most objects, the potential energy store is larger than the kinetic energy store. Increasing the potential energy can increase the overall internal energy without changing the temperature.
What is the equation that links work done to a system and the resultant temperature change?
-The equation that links work done to a system and the resultant temperature change is \(\Delta Q = mc\Delta T\), where \(\Delta Q\) is the energy transferred, \(m\) is the mass of the substance, \(c\) is the specific heat capacity, and \(\Delta T\) is the change in temperature.
What is the significance of the specific heat capacity of a substance?
-The specific heat capacity of a substance indicates the amount of energy required to raise the temperature of one kilogram of the substance by one degree Celsius. A larger specific heat capacity means more work is needed for a temperature increase.
How does the specific heat capacity affect the internal energy of a substance?
-A substance with a higher specific heat capacity will store more kinetic energy per temperature change, resulting in more internal energy and particles moving on average at a higher speed.
What is the direction of heat transfer in terms of temperature?
-Heat is always transferred from hotter substances to cooler substances, meaning it moves from areas of higher temperature to areas of lower temperature.
Can you provide an example calculation using the specific heat capacity equation from the script?
-Yes, to calculate the energy required to raise the temperature of 5 kilograms of water from 20°C to 100°C, using the specific heat capacity of water (4200 J/kg·K), the calculation is \(\Delta Q = 5 \text{ kg} \times 4200 \text{ J/kg·K} \times (100 - 20) \text{ K} = 1.7 \times 10^6 \text{ J}\).
Outlines
🔥 Introduction to Specific Heat Capacity
This paragraph introduces the concept of specific heat capacity within the realm of thermal physics, specifically for AQA A Level Physics. It discusses the calculation of specific heat capacity, the impact of work done on a system's internal energy, and the distinction between changes in kinetic and potential energy. The first law of thermodynamics is mentioned, highlighting the relationship between work done and changes in internal energy. The focus is on how work affects the kinetic energy store, leading to temperature changes. The direction of heat transfer is also explained, emphasizing the transfer from hotter to cooler substances and the role of temperature difference in heat transfer speed. The concept of internal energy change through work is reiterated, with an equation linking work done to temperature change (ΔQ = mcΔT).
💧 Understanding Specific Heat Capacity
This paragraph delves deeper into the concept of specific heat capacity, defining it as the energy required to raise the temperature of one kilogram of a substance by one degree Kelvin without changing its state. It explains the relationship between specific heat capacity, the kinetic energy store, and temperature change. The paragraph uses an example to illustrate how to calculate the energy needed to raise the temperature of water from 20°C to 100°C, using the specific heat capacity equation (ΔQ = mcΔT). The importance of units and significant figures in calculations is emphasized, and the direction of work done is related to temperature changes. The summary concludes with a recap of the lesson's objectives, reinforcing the understanding of how work is done into a system's internal energy and how to measure it using specific heat capacity.
Mindmap
Keywords
💡Specific Heat Capacity
💡Thermal Physics
💡Internal Energy
💡First Law of Thermodynamics
💡Kinetic Energy
💡Potential Energy
💡Heat Transfer
💡Temperature Change
💡Joules
💡Significant Figures
Highlights
Introduction to specific heat capacity as part of thermal physics in AQA A Level Physics.
Explaining how to calculate the specific heat capacity of a substance.
Defining specific heat capacity and its role in measuring work done into a system's energy.
Discussing the impact of work on internal energy and its two forms: kinetic and potential energy.
The first law of thermodynamics and its relation to changes in internal energy.
Heat transfer direction from hotter to cooler substances and its relation to particle energy.
Heat transfer mechanisms: conduction and radiation.
The effect of heating a substance on particle kinetic energy and temperature.
Equation linking work done to a system and temperature change: Δq = mcΔT.
Importance of units and significant figures in thermodynamics calculations.
Definition of specific heat capacity as energy needed per kilogram for a 1 K temperature change.
Implications of a substance's high specific heat capacity on internal energy storage.
Practical calculation example using the specific heat capacity equation.
Explanation of the calculation process for heating 5 kg of water from 20°C to 100°C.
Emphasis on the correct units and the significance of the temperature change in calculations.
Summary of the lesson's key learnings on specific heat capacity and its applications.
Closing remarks and a thank you note for watching the lesson on specific heat capacity.
Transcripts
hello and welcome to today's lesson on
specific heat capacity
which is part of the thermal physics
topic in aqa a level physics
so in today's lesson we're going to look
at how you can calculate the specific
heat capacity of a substance
so if we've been successful and learned
in today's lesson
we can explain how work can be done into
the internal energy of a system
we can define specific heat capacity of
a material
and we can measure the work done into
the energy of a system
using the internal energy of that system
so we're going to look at the following
part of the aqa a-level physics
specification
3.6.2.1 thermal energy transfer
now when work is done to the internal
energy of a system
that energy can be used to either
increase or
change the average kinetic energy of the
substance or it can be used to increase
the average potential energy
of the substance either one will change
the internal energy
now if you change the kinetic energy of
the internal energy
you'll be changing the temperature of
the substance if you change the
the potential energy stall of the
internal energy you'll be changing the
state
of the substance now you'll notice in
the diagram here we have a
representation
of the internal energy of a system now
for most
objects the potential energy store is
larger than the kinetic energy store
so as we said before if we increase the
potential energy we can
increase the overall internal energy now
remember
changing the internal energy of the
system is doing work
you must do work to change that internal
energy store of a substance
whilst also if we ch increase or change
the kinetic energy store of the
substance we will also be changing or
increasing
the internal energy we'll be doing work
again
now remember the change in internal
energy is equal to the work
done to the system this is the first law
of thermodynamics
now in this lesson we're only going to
be focusing on
how we increase or change the kinetic
energy store of the
internal energy of the system now an
increase in the kinetic energy store
of the internal energy would result in
an increase in the temperature of the
system
whilst a decrease in kinetic energy
store would result in a decrease in
temperature of the system
now it's important to note that heat is
always transferred from hotter
substances
to cooler substances so heat energy is
transferred
from higher temperatures to lower
temperatures so the direction of work
done is from an area of high temperature
to an area of low temperature now this
occurs because the particles with more
energy transfers some energy to the
particles with
less energy now the higher the
difference in temperature between the
two substances
the faster the heat transfer between the
substances
now as well as this idea of particles
with more energy transferring some
energy to particles with
less energy heat is also transferred by
radiation
so hotter substances will radiate heat
quicker
than cooler substances transferring that
heat energy to
the cooler cooler surroundings now
when you heat a substance the particles
in the substance
gain kinetic energy so when we say heat
is transferred into a substance
we say work is done into the system
because the
overall internal energy is increasing
now if we are placing heat energy into
the substance
the kinetic energy of the particles
increases
so therefore the temperature of the
substance itself
increases now doing work into or
out of a substance will cause a
temperature change in the
substance now the equation that links
work done
in an internal system and the resultant
temperature change of the substance
is it is the following delta q is equal
to mc
delta t where delta q is the energy
transferred the heat
transferred the work done m is the mass
of the substance
c is specific heat capacity and delta t
is the change in temperature of the
substance
now carrying out work into the system
placing heat into or out of the system
causes a change in the kinetic energy
stall and thus the temperature
now it's important to note that delta q
is energy transferred or work done so is
measured in joules
the mass is measured in kilograms and
the change in temperature
is measured in kelvins now it's
important to note that as this is a
delta t
it's a temperature change you can use
either celsius or kelvins
to actually work out this value because
the change in kelvin on the change in
celsius is the same value
now the last thing we need to look at is
specific heat capacity
now we can define heat capacity as the
energy supplied to a substance to change
the particle movement
to make the temperature change by one
kelvin
now that is heat capacity now specific
means per kilogram
so the specific heat capacity is the
energy needed
to raise one kilogram of a substance by
one degrees
kelvin without changing state so just to
clarify
the specific heat capacity is the link
between the kinetic energy store change
of the internal energy of the substance
and the resultant change in temperature
of the substance
now the larger the specific capacity
heat capacity of the substance
the more work is needed to be done to
raise the temperature by 1 degrees
celsius or kelvin now the larger the
specific heat capacity of a substance
the more kinetic energy is stored as
internal energy per
increase in temperature so what this
means
is that an object with a high specific
heat capacity
will store more kinetic energy per
temperature change
so we'll have more internal energy so if
you have
two materials which undergo the same
temperature change
the object which has the higher specific
heat capacity
will store more internal energy so
this means that the object with the
highest heat capacity
will have more internal energy so we'll
have a larger kinetic energy store and
have particles moving on average at a
higher speed
so let's now look at an example of a
calculation with the specific heat
capacity equation
so calculate the energy that must be
supplied to raise the temperature
of 5 kilograms of water from 20 degrees
to 100 degrees celsius
so the specific heat capacity of water
is 4200 joules per kilogram kelvin
now you will be given that in a question
in your examination
now the equation is delta q is equal to
mc
delta t now you'll have noticed in this
example i wrote delta t the change in
temperature as
t2 minus t1 the final temperature minus
the starting temperature
we then put our values in so 5.0 times
by 4200 times by
100 minus 20 which is 80. so we get our
answer
to be delta q the work done into the
system
is 1.7 times 10 to the 6 joules now
remember as the temperature change is
the same in degrees celsius as it is in
kelvin
that means if you were given temperature
in degrees celsius then you can
calculate the temperature difference
in that particular unit now you've
always got to remember as well
to give your answers with the correct
units and to the correct number of
significant figures
and finally always check to see if your
answer looks sensible
now again remember the direction in
which work is done
into the particular system now because
the temperature
is going higher it's going from 20 to
100 degrees
the work would be doing into the system
because the internal energy is getting
higher
so we can say that's 1.7 times 10 to the
6 joules is being placed
into the substance to cause this
temperature increase
obviously it will be the other way
around if it was a temperature decrease
so let's summarize what we've learned in
today's lesson
for a change in temperature q is equal
to m c delta theta
where c is specific heat capacity and in
this case delta theta
is the change in temperature so if we've
been successful and learned in today's
lesson
we should be able to explain how work
can be done into the
internal energy of a system we can
define specific heat capacity of
material
and finally measure the work done into
the energy of a system
using the internal energy of the system
so thank you very much for watching
today's lesson
on pacific heat capacity which is part
of the thermal physics topic
in aqa a level physics thank you very
much for watching and have
a lovely day
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