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2/3/10 Thermal Energy ΔEth = W + Q W = work done on system Q = heat added to system More Work and Heat What is ΔEth? Meaning of Temperature Thermal Energy We can’t change ΔEth without changing T Likewise, any change in T means a change in ΔEth But don’t confuse this with Q! A gas cylinder The piston can be locked in place A gas cylinder M = M1 + Mpiston M1 Consider an isochoric cooling process W = 0 How can we cool the gas? GAS Consider isothermal expansion ΔT = 0 What else = 0? So W = ‐Q Heat the gas but decrease M so that PV = constant M = M1 + Mpiston M1 GAS 1 2/3/10 A gas cylinder Consider isothermal expansion A gas cylinder M = M1 + Mpiston Consider adiabatic compression M = M1 + Mpiston M1 is NOT zero! M1 Adiabatic means Q=0 ΝΟΤΕ: ΔT = 0 but Q GAS If we compress the GAS gas, W > 0 Will ΔT = 0? Energy storage & transfer Consider two blocks of equal size The left block starts at 0 oC The right block starts at 100 oC What will happen? Energy storage & transfer Temperature Question Q = McΔT If we have a mass at Gases: Q = nCVΔT 20 oC and we double its temperature, what do we get? Q = nCPΔT 2