Thermal Energy  Temperature  Thermal Energy  Heat Transfer

Title: Temperature and Heat Temperature- a measure of the average value of the kinetic energy of the molecules in random motion (SI Unit for temp. is Kelvin (K)). Thermal Expansion- almost all substances expand when they are heated and contract when they are cooled-----except water! Thermal Energy- sum of the kinetic and potential energy of all the particles in an object; thermal energy of an object increasing as temperatures increases Temperature ConversionEquations o F  o C oC oFoC oF o C= (5/9)( o F-32) o F=(9/5) ( o C)+32

Heat- thermal energy that flows from something at a higher temperature to something at a lower temperature. Specific Heat- amount of heat needed to raise the temperature of 1kg of some material by 1 o C Thermal Energy Equation: (Q) Change in thermal energy(J)= Mass(kg)x temp( o C) x Specific heat(J/kg o C) Q=m(T f -T i )C SpecificHeat SubstanceJ/(kg o C) water4,184 wood1,760 carbon710 glass664 iron450

Temperature measure of the average KE of the particles in a sample of matter

Thermal Energy the total energy of the particles in a material KE - movement of particles (faster=more KE) PE - forces within or between particles due to position The sum of the kinetic and potential energy of all the particles in an object is the thermal energy of the object. depends on temperature, mass, and type of substance

Which beaker of water has more thermal energy? B - same temperature, more mass 200 mL 80ºC A 400 mL 80ºC B

Heat thermal energy that flows from a warmer material to a cooler material Like work, heat is... measured in joules (J) a transfer of energy

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.

Heat a. The flow of thermal energy from one object to another. b. Heat always flows from warmer to cooler objects. Ice gets warmer while hand gets cooler Cup gets cooler while hand gets warmer

C 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)

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.

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

Calorimeter device used to measure changes in thermal energy –in an insulated system, heat gained = heat lost

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

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