Heat is measured in Joules or calories. 1 cal = J Food energy in measured in Calories (with an upper case C) 1 Cal = 1000 cal
Essential Knowledge 4.C.3: Energy is transferred spontaneously from a higher temperature system to a lower temperature system. The process through which energy is transferred between systems at different temperatures is called heat. a. Conduction, convection, and radiation are mechanisms for this energy transfer. b. At a microscopic scale the mechanism of conduction is the transfer of kinetic energy between particles. c. During average collisions between molecules, kinetic energy is transferred from faster molecules to slower molecules.
Heat is transferred from the hot to the cold part of an object by the transfer of energy from atom to atom (or molecule to molecule) through the object. The atoms do not leave their equilibrium position. Only thermal energy moves through the object.
Convection is a process where heat is transferred from one place to another by mass that moves between the places and carries energy with it. This movement is due to differences in density. Radiation is a process of heat transfer involving a form of energy known as electromagnetic radiation. Evaporation is a cooling process due to continual escape of energetic, fast-moving molecules from a liquid.
Essential Knowledge 5.B.6: Energy can be transferred by thermal processes involving differences in temperature; the amount of energy transferred in this process of transfer is called heat.
Essential Knowledge 7.A.1: The pressure of a system determines the force that the system exerts on the walls of its container and is a measure of the average change in the momentum or impulse of the molecules colliding with the walls of the container. The pressure also exists inside the system itself, not just at the walls of the container.
Essential Knowledge 7.A.2: The temperature of a system characterizes the average kinetic energy of its molecules. a. The average kinetic energy of the system is an average over the many different speeds of the molecules in the system that can be described by a distribution curve. b. The root mean square speed corresponding to the average kinetic energy for a specific gas at a given temperature can be obtained from this distribution.
1. The number of molecules is large, and the average separation between them is large compared with their dimensions. 2. The molecules obey Newton’s laws of motion, but as a whole they move randomly. Randomly means that any molecule can move equally in any direction. 3. The molecules undergo elastic collisions with each other and with the walls of the container. Thus, in the collisions kinetic energy is constant. 4. The forces between molecules are negligible except during a collision. 5. The gas under consideration is a pure substance; that is, all molecules are identical.
Essential Knowledge 7.B.1: The approach to thermal equilibrium is a probability process. a. The amount of thermal energy needed to change the temperature of a system of particles depends both on the mass of the system and on the temperature change of the system. b. The details of the energy transfer depend upon interactions at the molecular level. c. Since higher momentum particles will be involved in more collisions, energy is most likely to be transferred from higher to lower energy particles. The most likely state after many collisions is that both systems of particles have the same temperature.