DHS 11 Temperature & Ideal Gases (Lecture Notes & Tutorial)

Dunman High School (Senior High Physics) 1 Topic 8 Temperature and Ideal Gases Guiding Questions:  What is the difference between temperature and heat? What is internal energy?  How can we define a simple model of a gas that is valid for real gases under certain assumptions?  How can we relate microscopic behaviour of gas molecules to the macroscopic properties of a gas? 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 degrees Celsius to kelvin: 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 21 3pV Nm c   , where N is the number of gas molecules (a simple model considering the one-dimensional collisions and then extending to three dimensions using 2 2 1 3 xc c    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. 21 3 2 2m c kT  ) to new situations or to solve related problems.

Dunman High School (Senior High Physics) 2 Introduction 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. Linking these two ideas is the zeroth law of thermodynamics, which states that when two objects at different temperature are placed in thermal contact, there will be energy exchange between them until thermal equilibrium is reached. The zeroth law allows the use of thermometers to measure temperature. When thermal equilibrium is achieved, the thermometer reflects its own temperature as well as the temperature of the other body that it is in thermal contact with. (a) show an understanding that regions of equal temperature are in thermal equilibrium. Temperature is a measure of degree of hotness of an object. Thermal energy moves from objects at a higher temperature to objects at a lower temperature. Note: temperature does NOT measure the amou