ASRJC Temperature and Ideal Gases Notes

ANDERSON SERANGOON JUNIOR COLLEGE PHYSICS 9749 8-1 Additional Notes Topic 8: Temperature and Ideal Gases Content: • Thermal equilibrium • Temperature scales • Equation of state • Kinetic theory of gases • Kinetic energy of a molecule Learning Outcomes: Candidates should be able to: (a) show an understanding that regions of equal temperature are in thermal equilibrium (b) explain how empirical evidence leads to the gas laws and to the idea of an absolute scale of temperature (i.e. the thermodynamic scale that is independent of the property of any particular substance and has an absolute zero) (c) convert temperatures measured in Kelvin to degrees Celsius: T/ K = T/ C + 273.15 (d) recall and use the equation of state for an ideal gas expressed as pV = nRT, where n is the amount of gas in moles (e) state that one mole of any substance contains 6.02 x 1023 particles and use the Avogadro number NA = 6.02 x 1023 mol-1 (f) state the basic assumptions of the kinetic theory of gases (g) explain how molecular movement causes the pressure exerted by a gas and hence derive the relationship pV = 1/3 Nm<c2>, where N is the number of gas molecules ( a simple model considering one -dimensional collisions and then extending to three dimensions using 1/3 <c2> = <cx2> is sufficient) (h) recall and apply the relationship that the mean kinetic energy of a molecule of an ideal gas is proportional to the thermodynamic temperature (i.e. ½ m <c2> = 3/2 kT) to new situations or to solve related problems Nature of Science Heat and temperature are often used interchangeably in everyday language. However, these terms have different and specific meanings in physics. Macroscopically, temperature can be defined in terms of its measurement, while heat refers to the energy transferred between two systems at different temperatures. Understanding thermal physics requires us to approach the concepts from both the macroscopic and microscopic lenses.

ANDERSON SERANGOON JUNIOR COLLEGE PHYSICS 9749 8-2 Additional Notes A.1 Temperature, Heat and Internal Energy • The temperature of a system is a measure of its average molecular kinetic energy. A higher temperature implies that the molecules in the system are moving faster on average. • Heating (thermal energy supplied) is a transfer of energy to an object resulting in an increase in the random kinetic and/or potential energies of the atoms or molecules of the object. • Internal energy is the sum of a random distribution of kinetic and potential energies associated with the molecules of a system. • When a body absorbs heat, two situations may arise: 1. The particles move further apart (increased molecular PE), causing an expansion. They also move more quickly on the average (increased molecular KE), causing a rise in temperature. 2. The particles move further apart (increased molecular PE), causing an expansion.