1. Temperature

2. 4 Main Things You Can Quantify About a Sample of Gas… Pressure (atm) Volume (L) Amount (mol) Temperature (K)

3. What is Temperature? It is a measure of the average kinetic energy of a group of particles

4. 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/KineticM olecularTheory/PT.html =

5. Kinetic Energy In any sample of gas, most particles have the same energy

6. Kinetic Energy But some particles have less energy than the average…

7. Kinetic Energy And some particles have more energy than the average…

8. Kinetic Energy Distribution As you heat up a sample of gas, the average kinetic energy of the particles increases

9. Kinetic Energy Distribution But even at high temperatures, some particles will still be moving slow…

10. Kinetic Energy Distribution And even at low temperatures, some particles will still be moving fast…

11. Explain This To Your Neighbor If the boiling point of water is 100 o C, how can it evaporate at 72 o C????

12. 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”.

13. 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.

14. Evaporation (lower temp) 100 o C Average Kinetic Energy is Low

15. Boiling (higher temp) 100 o C Average Kinetic Energy is High

16. How Low Can It Go? As temperature decreases, so does kinetic energy

17. How Low Can It Go? Theoretically, the temperature could get so low that Kinetic Energy would be zero

18. When Kinetic Energy is Zero… Particles stop moving!!! This is called absolute zero And it occurs at –273 o C

19. Temperature Scales Celsius Scale Based on the freezing and boiling point of water Water boils at 100 o C Water freezes at 0 o C Kelvin Scale Based on kinetic energy 0 K.E. = 0 Kelvins

20. Comparing the Temperature Scales An increase of 1 o C will result in an increase of 1K because they are the same size

21. Saying it Correctly… When reporting Kelvin temperatures we just say “Kelvins” not “degrees Kelvin”

22. Converting between o C and K The formula is Kelvins = o C + 273

23. Converting between o C and K The formula is Kelvins = o C + 273 Convert 25 o C to Kelvins K = 25 o C + 273 K = 298

24. Converting between o C and K The formula is Kelvins = o C + 273 Convert 308 K into o C 308K = __ o C + 273 308 – 273 = __ o C 35 o C

25. Practice Problems 1. If the temperature is 24.5 0 C. How many Kelvins is that? ____ 2. Water boils at _____ Kelvins. 3. Water freezes at _____ Kelvins. 4. Absolute zero is at _____ o Celsius. 5. If the temperature increases from 30 0 C to 38.5 o C, how many Kelvins does it increase by? 6. How many o C is 95 Kelvins?____

26. Answers 1. If the temperature is 24.5 0 C. How many Kelvins is that? 297.5 2. Water boils at 373 Kelvins. 3. Water freezes at 273 Kelvins. 4. Absolute zero is at -273 o Celsius. 5. If the temperature increases from 30 0 C to 38.5 o C, how many Kelvins does it increase by? 8.5 Kelvins 6. How many o C is 95 Kelvins?-178

27. Why Use Kelvins? Since Charles’ Law says V = kT If temperatures were in Celsius that would mean at O o C there would be no volume. But we know from experience that volumes still exist at 0 o C, the freezing point of water.

28. 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 pressure See the data on the following slides

29. Temperature vs. Volume Experiment This part of the data was “extrapolated”

30. Temperature vs. Pressure Experiment This part of the data was “extrapolated”

31. Let’s Try It Get a piece of graph paper Draw a graph with: ◦ Pressure on the y-axis ◦ Temperature on the x-axis Watch the video experiment and record the datavideo experiment ◦ Plot the data points and connect with a line ◦ Extend the line down to zero pressure What temperature is it at zero pressure?