Integrated Physics and Chemistry Thermal Energy Integrated Physics and Chemistry

THERMAL ENERGY AND HEAT 1.The kinetic theory of matter states that particles of matter are always in motion. Forces of attraction prevent the particles from drifting apart. 2. Thermal Energy is the total energy of all the particles in a sample of matter. Temperature is a measure of the average kinetic energy of a substance. The three factors that determine the amount of thermal energy are: mass, specific heat capacity and temperature of the object. 3. Heat is measured as a change in the amount of energy that is added to or removed from an object.

THERMAL ENERGY AND HEAT 4. The SI unit of thermal energy is the joule (J). The joule is the correct SI unit for measuring any form of energy. The calorie is defined as the quantity of heat needed to raise the temperature of one gram of water one Celsius degree. 1 calorie = 4.l8 joules. The energy content of food is often measured in Calories. The Calorie with a capital C is equal to one kilocalorie, or l000 calories.

THERMAL ENERGY AND HEAT 5. The Fahrenheit temperature scale is an English measurement scale. Water freezes at 32 ˚ F and boils at 212 ˚ F. The Fahrenheit degree scale is smaller than the Celsius degree or Kelvin. On the Celsius temperature scale, the freezing point of water is 0˚C and the boiling point is 100 ˚ C. The SI unit for temperature is the Kelvin (K). The Kelvin scale does not use the degree symbol. The units are Kelvins (K), not degrees Kelvin. One Kelvin equals one degree on the Celsius scale. On this scale the lowest possible temperature is absolute zero, written "O K." At absolute zero, the average kinetic energy of particles is zero. Absolute zero on the Kelvin scale is equal to -273 ˚ C.

THERMAL ENERGY AND HEAT 6. In a liquid thermometer, as the temperature rises, the liquid expands and rises in the tube. As the temperature falls, the liquid contracts and sinks in the tube. 7 Thermal energy is unique in that it does not exist by itself. That is, thermal energy is present only when another form of energy is present. 8. Thermal energy must be added to change phase from a solid or a liquid, or a liquid to a gas. Thermal energy must be removed to change phase from a gas to a liquid, or a liquid to a solid.

THERMAL ENERGY AND HEAT 9. If a solid substance is heated, it will melt and become a liquid. If a liquid is heated, it will boil and become a gas. If a gaseous substance is cooled, it will condense and become a liquid. If a liquid substance is cooled, it will freeze and become a solid. A liquid changes to a gaseous state by boiling or if heat is not added, by evaporation. Sublimation is the direct change of a solid to a gas or a gas to a solid without going through the liquid state.

THERMAL ENERGY AND HEAT 10. The temperature at which a solid becomes a liquid is called the melting point. The temperature at which a liquid becomes a gas at is called the boiling point. The temperature at which a gas becomes a liquid is called the condensation point and is the same temperature as the boiling point. The temperature at which a liquid becomes a solid is called the freezing point and is the same temperature as the melting point.

THERMAL ENERGY AND HEAT 11. The behavior of a substance as heat is added to it or removed from it can be summarized conveniently by a graph. One type of graph is a Phase Change Graph, which is a graph of temperature vs. time when the change in heat is constant and the substance changes phase.

THERMAL ENERGY AND HEAT

THERMAL ENERGY AND HEAT 12. As matter changes phase, thermal energy is absorbed or released until all particles of matter have changed phase. Therefore the temperature remains constant.

THERMAL ENERGY AND HEAT 13. Conduction, convection and radiation are the three different ways that thermal energy is transferred from one substance to another. Conduction is the transfer of thermal energy by direct contact between particles. Convection is heat transfer that occurs in moving fluids. Hot liquids and gases rise. Cold liquids and gases fall. This creates currents that carry thermal energy. Radiation is the transfer of thermal energy by waves. No particles are needed to transfer energy by radiation.