Temperature
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Temperature
description
Temperature. 0. 4 Main Things You Can Quantify About a Sample of Gas…. Pressure (atm) Volume (L) Amount (mol) Temperature (K). What is Temperature?. It is a measure of the average kinetic energy of a group of particles. What is Temperature?. - PowerPoint PPT Presentation
Transcript of Temperature
Temperature
4 Main Things You Can QuantifyAbout a Sample of Gas…
Pressure (atm)Volume (L)
Amount (mol)Temperature (K)
What is Temperature?
It is a measure of the average kinetic energy of a group of
particles
What is Temperature?
When temperatures are high, many particles have a lot of
kinetic energy and move around very quickly
http://www.chm.davidson.edu/vce/KineticMolecularTheory/PT.html
=
Kinetic Energy
In any sample of gas,most particles have the same
energy
Kinetic Energy
But some particles have less energy than the average…
Kinetic Energy
And some particles have more energy than the average…
Kinetic Energy Distribution
As you heat up a sample of gas, the average kinetic energy of the particles increases
Kinetic Energy Distribution
But even at high temperatures, some particles will still be moving
slow…
Kinetic Energy Distribution
And even at low temperatures, some particles will still be moving
fast…
Explain This To Your Neighbor
If the boiling point of water is 100o C,how can it evaporate at 72oC????
How can water evaporate at temperatures below its boiling point?
To change from liquid to gas, a molecule must break the attractive force (shown by green dots) it has with its neighbor. These
are called “intermolecular forces”.
How can water evaporate at temperatures below its boiling point?In any sample, the particles have a range of
kinetic energies so there are always some particles with enough energy to break this attraction and escape into the gas phase.
At higher temperatures, it happens faster (boiling) because more particles have a lot
of kinetic energy.
Evaporation (lower temp)
100o C
Average Kinetic
Energy is Low
Boiling (higher temp)
100o CAverage
Kinetic
Energy is High
How Low Can It Go?
As temperature decreases,so does kinetic energy
How Low Can It Go?
Theoretically, the temperature could get so low that Kinetic
Energy would be zero
When Kinetic Energy is Zero…
Particles stop moving!!!This is called absolute zero
And it occurs at –273oC
Temperature Scales
Celsius Scale
Based on the freezing and
boiling point of water
Water boils at 100oC
Water freezes at 0oC
Kelvin Scale
Based on kinetic energy
0 K.E. = 0 Kelvins
Comparing the Temperature Scales
An increase of 1oC will result in an increase of 1K because they are the same size
Saying it Correctly…
When reporting Kelvin temperatures we just say
“Kelvins” not “degrees Kelvin”
Converting between oC and K
The formula isKelvins = oC + 273
Converting between oC and K
The formula isKelvins = oC + 273
Convert 25oC to KelvinsK = 25oC + 273
K = 298
Converting between oC and K
The formula isKelvins = oC + 273
Convert 308 K into oC308K = __oC + 273308 – 273 = __oC
35oC
Practice Problems1. If the temperature is 24.50C. How
many Kelvins is that? ____2. Water boils at _____ Kelvins.3. Water freezes at _____ Kelvins.4. Absolute zero is at _____ oCelsius.5. If the temperature increases from
300C to 38.5oC, how many Kelvins does it increase by?
6. How many oC is 95 Kelvins?____
Answers1. If the temperature is 24.50C. How
many Kelvins is that? 297.52. Water boils at 373 Kelvins.3. Water freezes at 273 Kelvins.4. Absolute zero is at -273 oCelsius.5. If the temperature increases from
300C to 38.5oC, how many Kelvins does it increase by? 8.5 Kelvins
6. How many oC is 95 Kelvins?-178
Why Use Kelvins?
Since Charles’ Law says V = kT
If temperatures were in Celsius that would mean at OoC there
would be no volume.
But we know from experience that volumes still exist at 0oC, the
freezing point of water.
Deep Thought…
If we’ve never reached absolute zero, how do we know what
temperature it is?
By doing experiments where the data is “extrapolated” (extended based on the visual trend) to zero volume
or pressureSee the data on the following
slides
Temperature vs. Volume Experiment
This
part o
f
the
data
was
“ext
rapola
t
ed”
Temperature vs. Pressure Experiment
This part
of
the data
was
“extra
polat
ed”
Let’s Try ItGet a piece of graph paperDraw a graph with:
◦Pressure on the y-axis◦Temperature on the x-axis
Watch the video experiment and record the data◦Plot the data points and connect with
a line◦Extend the line down to zero
pressureWhat temperature is it at zero
pressure?
