Transferring Thermal Energy Unit 1 Physical Science HS Credit Mrs. Rubel

Temperature and Heat There is no such thing as cold – just the absence of heat. The temperature of a material is a measure of the average kinetic energy of the molecules in the material. Heat is a thermal energy that flows from a higher to a lower temperature.

Temperature and Heat The thermal energy of an object is the total potential and kinetic energy of the molecules in the object. The specific heat is the amount of heat needed to raise the temperature of 1 g of a substance by 1oC

Heat and Its Measurement Heat energy (Q) can be measured in units of calories (Cal) or joules (J). When there is a temperature change (Δ), you find the heat energy by mass x ΔT x the specific heat capacity of the substance.

Heat and Its Measurement Example: How many joules of heat are given off when 8.0 g of water cool from 80oC to 20oC? The specific heat of water is 4.18 j/goC. Mass = 8.0 ΔT = - 60 specific heat = 4.18 Q = Mass x ΔT x specific heat Q = 8.0 x - 60 x 4.18 = - 2006.4 J

Heat and Its Measurement If you are measuring heat during a phase change, then use the formula Q = mass x heat of fusion (freezing) or vaporization Ex: How many calories are given off when 60g of water at 0oC freezes? The heat of fusion is 79.72 cal/g. Q = 60g x 79.72 = 4783.2 Cal

Transferring Thermal Energy 1) Conduction – when thermal energy is transferred by “touch,” through a collision of particles. Matter is not transferred, only energy.

Transferring Thermal Energy 2) Convection – In science, fluids can be liquids or gases. Convection occurs in a fluid as warmer and cooler fluid move from place to place.

Transferring Thermal Energy 3) Radiation – the transfer of energy by electromagnetic waves. Radiation can transfer energy through open space.

Transferring Thermal Energy Heat flows more easily in materials that are conductors, such as metals. Conductors tend to have little space between the particles. A material in which heat flows slowly is an insulator. Plastic, fiberglass, and air are examples. Some insulating materials contain pockets of trapped air that reduce the flow of heat.

Using Heat Conventional heating systems use air, hot water, and steam to transfer thermal energy through a building. A solar heating system converts radiant energy from the Sun to thermal energy. Solar collectors absorb the thermal radiant energy.

1st Law of Thermodynamics States that the increase in thermal energy of a system equals the work done on the system; and the amount of heat added to that system. Example: bicycle pump (see page 175)

2nd Law of Thermodynamics States that heat cannot flow from a colder to hotter temperature unless work in done, and that heat cannot be converted completely into work. This can’t actually happen, because no work can be done. Example: holding an ice cube in your hand is not work.