Presentation on theme: "Ch. 5 - Energy II. Thermal Energy (p.134-137, 141-144) Temperature Thermal Energy Heat Transfer."— Presentation transcript:
Ch. 5 - Energy II. Thermal Energy (p , ) Temperature Thermal Energy Heat Transfer
A. Temperature Temperature measure of the average KE of the particles in a sample of matter
Measuring Temperature A thermometer is a instrument for measuring temperature. Uses a standard for comparison. Examples: Celsius, Fahrenheit, and Kelvin Scales
Celsius Scale ( o C) Based on freezing point (0 o C) and boiling point (100 o C) of water Standard metric scale for measuring particle temperature
Kelvin Scale (K) Using absolute zero as a standard Absolute zero is the temp. where kinetic molecular motion stops Conversion: ( o C)= Kelvin
Temperature vs. Heat Temperature: A measure of average kinetic energy of an object Use standard scales: (K), ( o C) Temp. is not a measure of the total amount of energy in an object
Temp. vs. Heat Heat: Energy given off or absorbed by an object Measures the motion of molecules in an object Measured in Calories
B. Thermal Energy Thermal Energy the total energy of the particles in a material KE - movement of particles PE - forces within or between particles due to position depends on temperature, mass, and type of substance
B. Thermal Energy Which beaker of water has more thermal energy? B - same temperature, more mass 200 mL 80ºC A 400 mL 80ºC B
Thermal Energy Cont. Total energy of the particles in a material A sum of both kinetic and potential energy A more massive object has more thermal energy at the same temperature than a less massive object.
C. Heat Transfer Heat thermal energy that flows from a warmer material to a cooler material Like work W=F x d, heat is... S.I. unit is Calories Often measured in joules (J) a transfer of energy
C. Heat Transfer Why does A feel hot and B feel cold? 80ºC A 10ºC B Heat flows from A to your hand = hot. Heat flows from your hand to B = cold.
C. Heat Transfer Specific Heat (C p ) amount of energy required to raise the temp. of 1 kg of material by 1 degree Kelvin units: J/(kg·K) or J/(kg·°C)
Specific Heat Cont. The ability of a substance to absorb heat energy (specific heat) Different substances absorb heat at different rates (land versus water) The greater the mass of an object the more heat it absorbs
C. Heat Transfer Which sample will take longer to heat to 100°C? 50 g Al50 g Cu Al - It has a higher specific heat. Al will also take longer to cool down.
C. Heat Transfer Q = m T C p Q:heat (J) m:mass (kg) T:change in temperature (K or °C) C p :specific heat (J/kg·K) T = T f - T i – Q = heat loss + Q = heat gain
C. Heat Transfer Calorimeter device used to measure changes in thermal energy Coffee cup Calorimeter in an insulated system, heat gained = heat lost
C. Heat Transfer A 32-g silver spoon cools from 60°C to 20°C. How much heat is lost by the spoon? GIVEN: m = 32 g T i = 60°C T f = 20°C Q = ? C p = 235 J/kg·K WORK: Q = m· T·C p m = 32 g = kg T = 20°C - 60°C = – 40°C Q = (0.032kg)(-40°C)(235J/kg·K) Q = – 301 J
C. Heat Transfer How much heat is required to warm 230 g of water from 12°C to 90°C? GIVEN: m = 230 g T i = 12°C T f = 90°C Q = ? C p = 4184 J/kg·K WORK: Q = m· T·C p m = 230 g = 0.23 kg T = 90°C - 12°C = 78°C Q = (0.23kg)(78°C)(4184 J/kg·K) Q = 75,061 J
Forms of Heat Transfer Three forms of Heat Transfer: (6.1- pgs ) Conduction Convection Radiation
Conduction Conduction involves the transfer of heat through direct contact Heat conductors conduct heat well, insulators do not
Convection Takes place in liquids and gases as molecules move in currents Heat rises and cold settles to the bottom Creates weather patterns and ocean currents
Fluid Convection Currents are formed be the movement of liquids and gases from warmer to cooler areas.
Radiation Heat transferred through space Energy from the sun being transferred to the Earth
Thermal Pollution ( ) Occurs when waste heat significantly changes the temperature of an environment Warmed water from factories decreases dissolved oxygen in water