# Temperature, Heat & Heat Transfer

Pages: 12 (3471 words) Published: October 5, 2013
﻿Chapter 15 & 16: Temperature, Heat & Heat Transfer
Temperature is a measure of the average (not total) translational kinetic energy. ●ex: there is 2x as much total molecular kinetic energy in a 2L of boiling water than one, but the temp of the two volumes are the same (average of translational kinetic energy per molecule is the same in each → Internal Energy- the total of all molecular energies: kinetic+potential (SAME TEMP) ● Ex: apply a flame to 1L h2o for a certain time and its temp rises by 2C, if you apply the same flame for the same time to 2L how much will the temp rise? 1C because there are 2x as many molecules in 2L and each relieves only ½ as much energy on the average ● molecules with more KE that are in contact w/ molecules w/ less KE transfer some of their excess energy to the less kinetic ones( like heat). Direction of energy is hot→cold ●the more massive the object the more molecules = more total energy-internal energy → Specific Heat- amount of heat needed to change mass

● C=specific heat C=Heat/mass x change in temp ex: how many cal are neeed to raise by 50C the temp of 300 g of aluminum. Aluminum c= .2.14 cal/ gm C →Thermal Expansion- heat expands

●high end- no limit to how hot an object can get (plasma) ●low end- absolute zero, thermal motion ceases → Heat Transfer: transfer of thermal energy (measured by effects produced) ●conduction- transfer of heat energy by molecular and electron collisions w/in a substance (solids) ● 3 factors that conduct better: 1) larger area 2) thickness-slows heat from inside to outside 3) material ●good conductor of heat: metals●bad conductor of heat: air ●convention- the transfer of heat energy in a gas or liquid by means of currents in the heated fluid... fluids move carring energy with it (actual movement from one location to another)

●hot air rises(less dense than cool air)
●radiation- the transfer of energy through by electromagnetic waves (infrared)
●good absorbers= good emitters (black objects)
●good reflectors (shiny objects) = poor absorbers of radiation ●Greenhouse effect- waves are trapped and reflected back by atmosphere and glass, warming up trapped place ●everything w/ any temp above absolute zero emits electromagnet energy ●ex: inside your home or classroom you are comfortable only if the walls are warm, not just the air Chapter 17: Change of Phase

●occur at a constant temp
●Evaporation/melting- liquid to gaseous
●heat added increases PE of molecules
● is a cooling process because heat increases PE which breaks bonds and molecules are able to escape the liquid ●sublimation – from solid to gaseous, bypassing the liquid phase (dry ice) ●condensation/freezing- gaseous to liquid

●heat removed decreases PE of molecule (removing heat only removes KE not PE) ● can you conclude that no evap or condensation occurred if the water in a dish remained changed after a day? No both evap and conden occur continuously: equal rates of both→ two processes cancel each other out ●boiling- rapid evap that takes place w/in a liquid as well as its surface

●does not increase in temp when additional heat is applied because the increased heating produces increased boiling and therefore increased cooling ●Regelation-process of melting under pressure and the refreezing when pressure is removed ●heat pump- device that transfers heat out of a cool environment & transfers it to warm ●latent heat- energy required to change substance from solid to liquid

●H (latent heat) =L x m (mass in gm)
●solidliquid= melting
●L_V=540 cal/gram (heat of vap-fog and clouds)
● law used to calculate heat transfer to change the temp by a certain number of degrees? Specific heat/ heat capacity ● Q_total= Q_melting + Q_water + Q_freezing
● Qmelting= (L_f x M)
●Qfreezing= (L_v x M)
●Qwater=C x M ∆T ( heat capacity x mass x change in temp) ●Ex 1: ? cal does it take to change 50gm of ice at 0C to water at 40C?
Qm= L_f x M...