Isobaric Process Constant pressure process. Isovolumetric Process Constant volume process. If volume doesn’t change work cannot be done to compress the gas. Isothermal Process Constant temperature process. If you do work to compress a gas the energy you put in is released through heat. On a PV – diagram it is common to use isotherms to show how the temperature changes for a process. Isotherm – Hyperbolic line of constant temperature on a PV – diagram.

This is a PV – diagram showing several isotherms. Isobaric Process Isovolumetric Process What type of process is described by each of the arrows? Isothermal Process Adiabatic Process

A cylinder with a piston on top contains a compressed gas and is sitting on a thermal reservoir (a large iron block). After everything has come to thermal equilibrium, the piston is moved upward somewhat (very slowly). The object to be considered is the gas in the cylinder. (Q) The object is absorbing or giving off heat. (T) The object's temperature is changing. (U) The object's internal energy is changing. (W) The object is doing mechanical work or having work done on it Use the letters defined above to identify all the changes that are occurring in the system. W W, Q W, U W, Q, T W, T, U Q, T, U W, Q, T, U None

A cylinder with a piston on top contains a compressed gas and is wrapped in styrofoam, a very good thermal insulator. After everything has come to thermal equilibrium, the piston is pressed downward (very slowly). The object to be considered is the gas in the cylinder. (Q) The object is absorbing or giving off heat. (T) The object's temperature is changing. (U) The object's internal energy is changing. (W) The object is doing mechanical work or having work done on it Use the letters defined above to identify all the changes that are occurring in the system. W W, Q W, U W, Q, T W, T, U Q, T, U W, Q, T, U None

Energy Transfer Mechanisms What are the three different ways in which energy can be transferred from one object to another? Conduction, Convection and Radiation Conduction – Energy transfer through contact. – Kinetic energy is exchanged due to collisions between adjacent molecules. There two material classifications we give to describe the efficiency of transferring energy through thermal contact. Conductors – Materials that easily transfer energy through contact. Examples: Metals Insulators – Materials that are poor at transferring energy through contact. Examples: Wood, rubber, paper, fiberglass Pushed by rising parcel Convection - Energy transfer through the motion of a fluid (liquid or gas). Cools, density increases Rises due to decreased density Fluid Parcel Radiation - Transmission of energy through electromagnetic waves. pushed into vacancy Heat

CH 19: ideal gases

Ideal Gas Ideal gases are defined as gases at low pressure, or gases that have a low density. We use ideal gases to approximate the more complex relationships that can exist. Relationships between the pressure, volume and temperature are called equations of state. These equations can be very complicated. A relationship between pressure , volume and temperature can be found for ideal gases and is much simpler than the more complex general equations of state. The equation of state for an ideal gas called the ideal gas law shows this relationship. P – pressure [atm, Pa] V – Volume [m3, L] T – Temperature [K] R – Universal gas constant = 0.08214 L atm/mol K n – Number of moles m – mass of sample [g] Mm – Molar mass [g/mol] N – Number of molecules [molecules] NA – Avogadro’s Number of molecules per mole [molecules/mol] The ideal gas law is essentially an energy relation. kB – Boltzmann’s Constant kB = R/NA = 1.38x10-23 J/K

Example: A container of an ideal gas has a moveable top Example: A container of an ideal gas has a moveable top. The top has an area of 0.01 m2 and is 50 cm above the bottom of the cylinder. A mass of 200 kg is placed on the container, which compresses the gas by 20 cm. The gas in the container is initially at atmospheric pressure (1.01 x 105 Pa) and 20oC. What is the new temperature of the gas?

A few ml of water is heated in a 12-ounce soda can (photograph at left below) until the water boils, producing steam as evidenced by the condensation coming out of the can (photograph at the center below). The steam-filled can is then grabbed by a pair of tongs and quickly placed upside down on a dish of room-temperature water. When the can reaches the surface of the water: (1) The can will RAPIDLY implode. (2) The can will SLOWLY implode. (3) Water will be pulled up into the can, filling the can with water. (4) Nothing will happen.