1. Thermal Concepts
Heat & Thermodynamics

2. Objectives
State that the temperature determines the direction of thermal energy transfer
State the relation between the Kelvin and Celsius temperature scales

3. Thermal Energy (Heat) Transfer
State that the temperature determines the direction of thermal energy transfer TEMPERATURE: A measurement of how hot an object is. A scalar quantity. If two objects have the same temperature, there will be no net heat flow between them. Heat energy moves from ‘hotter’ to “colder” bodies.

4. What happens when two objects have the same temperature?
When two bodies are at the same temperature as each other, they are in thermal equilibrium.
This leads to the ‘Zeroth’ law of thermodynamics’: If two bodies A and B are separately in thermal equilibrium with body C, they are also in thermal equilibrium with each other and thus have the same temperature.

5. “Cold” is the word assigned to a lack of heat energy.
“Cold” isn’t real
“Cold” is the word assigned to a lack of heat energy.

6. The Cosmic Microwave Background 2.72548±0.00057 K

7. State the relation between the Kelvin and Celsius temperature scales
The absolute temperature scale (measured in Kelvin and with a minimum value of zero Kelvin) is used in physics calculations.
(Where a change of one Kelvin equals a change of one degree Celsius)
(i.e. The KE of the particles is directly proportional to the temperature)
Kelvin Temperature = Celsius Temperature + 273
The absolute (Kelvin) temperature of a body is a measure of the average amount of kinetic energy that each of its molecules have.

8. Practice Convert 25.0 °C to Kelvin. Convert 375 K to degrees Celsius.
Convert −50 °C to Kelvin. (That's a minus 50.)
The boiling point of water on the Kelvin scale is __________.
40.0 °C is what temperature on the Kelvin scale?
-20.0 °C is what temperature on the Kelvin scale?
298 K is what temperature in degrees Celsius?
What is the temperature (give in both °C and K) at STP?
Convert °C to K
Convert 20.0 °C to K
Convert 252 K to °C
298 K
102 °C
223 K
373 K
313 K
253 K
25 °C
0 °C or 273 K
128 K
293 K
-21 °C

9. Objectives
State that the internal energy of a substance is the total potential energy and random kinetic energy of the molecules of the substance.
Explain and distinguish between the macroscopic concepts of temperature, internal energy and thermal energy (heat).

10. Absolute Zero
The lowest temperature possible °C or zero kelvin (0K). Kelvin is the absolute thermodynamic temperature scale. Particles have no kinetic energy at 0 K.
INTERNAL ENERGY: The energy contained in an object due to the random KE and PE of the molecules.
The kinetic energy of molecules arises from their random/translational/rotational motion and the potential energy arises from the forces between the molecules.

11. State that the internal energy of a substance is the total potential energy and random kinetic energy of the molecules of the substance.
Potential Energy
Random Kinetic Energy

12. Explain and distinguish between the macroscopic concepts of temperature, internal energy and thermal energy (heat).

13. Thermal Energy
The term thermal energy refers to the non-mechanical transfer of energy between a system and its surroundings. In this respect it is just as incorrect to refer to the “thermal energy in a body” as it would be to refer to the “work in a body”.

14. Summary
Write a paragraph comparing the macroscopic concepts of temperature, internal energy and thermal energy (heat).

15. Objectives
Define the mole and molar mass
Define the Avogadro Constant

16. Define the mole and molar mass
MOLE: The amount of a substance that contains the same number of particles as there are atoms in 12g of carbon-12.
MOLAR MASS: The mass of 1 mole of a substance. eg molar mass of water is 18g
Define the Avogadro Constant
The number of particles in a mole. A=6.02 x 1023

17. Moles & the Avogadro Number
The number of molecules in a substance is measured in ‘moles’. Just like ‘a dozen’ means twelve of something, ‘one mole’ means 6.02 x molecules of something.
One mole of a substance contains the same number of molecules as in 12 grams of Carbon-12.
The Avogadro number (NA) is equal to the number of molecules in 12 grams of Carbon-12 (NA= 6.02 x 1023)
The molar mass (M) is the mass in grams of one mole of a particular substance.
Note: the mass number of an element is equal to the molar mass for atoms of an element.
E.g. One mole of Nitrogen atoms will have mass 14g.

18. Examples
The mass number of Helium is 4. How many atoms are in 4kg of Helium?
Mass no. is 4 so molar mass is 4g.
4000 g / 4g = 1000 moles
1000 x NA = (1 x 103) x (6.02 x 1023)
= 6.02 x 1026 atoms

19. Examples
2. The molar mass of iron atoms is 56 g mol-1 and its density is 7.9 g cm-3.
Find the mass of one atom of Iron.
Calculate the number of iron atoms in one cubic metre of iron.

20. Examples
2. The molar mass of iron atoms is 56 g mol-1 and its density is 7.9 g cm-3. a. If one mole of atoms has mass 56g then one atom will have mass = 56 ∕ NA = 56 ∕ (6.02 x 1023) = 9.3 x 10-23g b. Calculate the number of iron atoms in one cubic metre of iron. One cm3 has mass = 7.9 g So one m3 has mass = 7.9 x (100x100x100) g = 7.9 x 106 g So # of iron atoms per m3 = 7.9 x 106 / 9.3 x = 8.5 x 1028 atoms

21. MOLES
The number of moles of a substance (n) can be determined form the total mass (m) divided by the molar mass (mass per mole, M), usually both measured in grams: Similarly if you knew the total number of molecules (N), you could find the number of moles (n) from…
n = m M
n = N NA

22. Examples
Calculate the number of moles of oxygen atoms in 40g of oxygen. Calculate the number of moles of oxygen molecules (O2) in 40g of oxygen. A sample of fluorine gas contains 20 x 1023 atoms of fluorine. Calculate the number of moles present.

23. Examples
Calculate the number of moles of oxygen atoms in 40g of oxygen. N = m / M = 40 / 16 = 2.5 moles Calculate the number of moles of oxygen molecules (O2) in 40g of oxygen. N = m / M = 40 / 32 = 1.25 moles A sample of fluorine gas contains 20 x 1023 atoms of fluorine. Calculate the number of moles present. N = N / NA = 20 x 1023 / 6.02 x 1023 = 3.3 moles

24. Complete the assigned problems for whiteboards tomorrow!
Your turn!
Complete the assigned problems for whiteboards tomorrow!