1. HEAT AND THERMAL ENERGY Kinetic Theory of Gases Thermal Expansion Gas Laws

2. HEAT AND THERMAL ENERGY Postulates o f the Kinetic Theory of Gases There are a large number of molecules moving in random directions with a variety of speeds. The average distance between the molecules is much greater than the diameter of each molecule.

3. HEAT AND THERMAL ENERGY Postulates o f the Kinetic Theory of Gases Molecules only interact when they collide with each other or with the walls of the container. These collisions are perfectly elastic. The absolute (Kelvin) temperature is directly proportional to the average translational kinetic energy. Temperature does not measure heat!

4. HEAT AND THERMAL ENERGY Sample Question A piece of metal has a temperature of 0 degrees Celsius. A second piece of metal has a temperature twice as great. What is its temperature?

5. HEAT AND THERMAL ENERGY DEFINITIONS THERMAL ENERGY (or internal energy) - the sum of all the energies (such as rotational, kinetic and vibrational) of all the molecules in an object. HEAT - the thermal energy which transfers from one body to another due to a temperature difference.

6. HEAT AND THERMAL ENERGY THERMAL EXPANSION Substances expand when heated because of the increase in molecular motion. Substances contract when cooled because of the decrease in molecular motion.

7. HEAT AND THERMAL ENERGY THERMAL EXPANSION For one-dimensional expansion:  L =  L 0  T (   coefficient of linear expansion) For three-dimensional expansion:  V =  V 0  T (  = coefficient of volume expansion)

8. HEAT AND THERMAL ENERGY THE GAS LAWS OBJECTIVE: To use the kinetic theory of gases to explain three experimental results: Boyle's Law Charles' Law Gay-Lussac's Law And to use these results to derive the equation of state for ideal gases.

9. HEAT AND THERMAL ENERGY BOYLE’S LAW The volume of a gas is inversely proportional to the pressure applied to it when the temperature is kept constant. V  1/P (constant temperature)

10. HEAT AND THERMAL ENERGY CHARLES’ LAW The volume of a given amount of gas is directly proportional to the absolute temperature when the pressure is kept constant. V  T (constant pressure) This law leads to the concept of absolute zero. Since there is a minimum for volume, there must be a minimum for temperature.

11. HEAT AND THERMAL ENERGY GAY-LUSSAC’S LAW At constant volume, the pressure of a gas is directly proportional to the absolute temperature. P  T (constant volume)

12. HEAT AND THERMAL ENERGY THE GAS LAWS Let’s put it all together: PV  constant (Boyle’s Law) V  T (Charles’ Law) P  T (Gay- Lussac’s Law) If we combine these three laws we get: PV  T

13. HEAT AND THERMAL ENERGY THE GAS LAWS Another way to increase pressure at a constant volume and temperature is to add more gas (i.e. where n is the number of moles of gas). This finally gives us the equation of state. PV = nRT where n is the number of moles of gas. One mole is the amount of substance that contains as many atoms or molecules as there are in 12.00 grams of carbon 12 (12 amu). It is also the number of grams of a substance numerically equal to the molecular mass of the substance.