2nd Law of Thermodynamics: HW 12-2 AND 12-3 Heat always flows from to HOT COLD Heat transfer Khan IR Camera

Heat ≠ Temperature Bozeman temp Temperature : proportional to average kinetic energy of particles (Units: K (Kelvin) ; oC (Celcius) Heat – energy that flows from a hotter object (higher temperature) to a colder object (lower temperature) (Units: J (joule) WORK HW 12-2

NO, values range from 5 to 15

50 ÷ 5 = 10 J KINETIC ENERGY

HEAT WILL FLOW FROM HOT (SYSTEM #1) TO COLD (SYSTEM #2) #1: 30 ÷ 3 = 10 #1: 12 ÷ 3 = 4 10 4 #1; Higher Average KE HOT TO COLD HEAT WILL FLOW FROM HOT (SYSTEM #1) TO COLD (SYSTEM #2)

#1: 21 ÷ 3 = 7 #2: 21 ÷ 3 = 7 7 7 TEMPERATURE ARE EQUAL (SAME AVERAGE KE; THERMAL = HEAT EQUILIBRIUM = BALANCE ; TEMPERATURES ARE EQUAL

THERMAL EQUILIBRIUM

HW 12-3 CONCEPT OF HEAT

Is the amount of material (mass) important in heat transfer? B) The cup will have the higher final temperature; Each individual molecule absorbs more energy

$1 $100

When same total amount of energy is distributed amongst a smaller number of molecules, each individual molecule receives more energy. 10 energy units split 5 ways 10 Energy Units split 2 ways Link to video Higher Temp, each molecule has more KE

Finish the rest of 12-3 CONTAINER #1 = $500 CONTAINER #1 CUP BUCKET OF WATER

#1: 24 ÷ 6 = 4 #2: 12 ÷ 3 = 4 4 4 24 12 TEMPERATURES ARE SAME; SAME AVERAGE KINETIC ENERGY CONTAINER #1 HAS STORED MORE TOTAL HEAT 24 vs 12

#1: 300 ÷ 3 = 100 #2: 500 ÷ 10 = 50 100 50 300 500 CONTAINER #1 ; HIGHER AVERAGE KINETIC ENERGY CONTAINER #2 HAS STORED MORE TOTAL HEAT 500 vs 300

Do all objects absorb and store heat in the same way Do all objects absorb and store heat in the same way? If both cars are left in the sun in the senior lot for the same amount of time will the interiors be at the same temperature at lunch time? Black Porsche White Porsche

Do both of these materials store heat in the same way? Water Rock

“s” is Specific Heat Capacity s = amount of energy needed to raise the temp of 1 g of a substance by 1ºC. H2O: s = 4.18 J/gºC Rock: s = 0.6 J/gºC How much energy in J must be added to 1 g of H2O to raise its temp by 1 oC? How much energy in J must be added to 1 g of rock to raise its temp by 1 oC? 4.18 J 0.6 J

HW 12-3, #8 OCEAN (4.18 J/ goC) ROCK (0.6 J/ goC) MORE energy must be absorbed to raise T. MORE energy must be lost to lower T. LESS energy must be absorbed to raise T. LESS energy must be lost to lower T

HW 12-3, #9 COPPER (0.13 J/ goC) ALUMINUM (0.89 J/ goC) Stores less energy when raising Temp; Releases less energy when lowering Temp Stores less energy when raising Temp; Releases less energy when lowering Temp

ALUMINUM HAS HIGHER HEAT CAPACITY; Al HAS MORE HEAT ENERGY STORED at 100 oC THAN Cu. WATER ABSORBS MORE HEAT FROM Al AND REACHES HIGHER FINAL TEMP.

Q = s×m×ΔT Q = heat absorbed or lost +Q if absorbed, -Q if lost Copy at bottom of p. 128; write equation on top of 129. Q = s×m×ΔT Q = heat absorbed or lost +Q if absorbed, -Q if lost m = mass in grams ΔT = temperature change: Δ T = Tfinal – Tinitial s = specific heat capacity units of s are J/gºC

EXAMPLE PROBLEM Q = 1.77 x 105 J Q = ? or x m = 454 g Calculate J of energy required to heat 454 g of water from 5.4oC to 98.6 oC. s of H2O = 4.18 J/g oC. Q = ? or x m = 454 g Ti = 5.4 oC ; Tf = 98.6 oC ; ∆T = Tf - Ti = 98.6 -5.4 =93.2 oC Q = sm ∆T = (4.18 J/ g oC)(454 g)(93.2 oC) Q = 1.77 x 105 J