Heat Transfer Problems

12-4 – Case #1 Silver Spoon Steel Spoon m = 10.0 g m = 10.0 g Boiling Water Baths at 100 oC Ti = 25.0 oC Ti = 25.0 oC s = 0.233 J/ g oC s = 0.51 J/ g oC

Graph of Temp v Time T emp E R A U 100 oC Silver silver steel Time 20 minutes 2) At 20 min, both metals have equilibrated to the temp. of surroundings.

3) Which Spoon’s atom’s have a greater average kinetic energy? Temperature is directly proportional to average kinetic energy. BOTH ARE AT SAME TEMPERATURE THUS KINETIC ENERGIES ARE THE SAME.

HW 12-4 #4) Which spoon has more stored heat Q? Steel. It takes 0.51 J to raise the temp. of 1 g of Steel by 1oC. It takes only .23 J of energy to raise the temperature of 1 g of silver by 1 oC.

4) Calculate Q absorbed after 20 min. TF = 100oC of spoons; Q = sm∆T Silver: Q = (0.23 J/g oC)(10.0 g) (100oC – 25oC) Q = 172. 5 = 170 J (2 SF) Steel: Q = (0.51 J/g oC)(10.0 g) (100oC – 25oC) Q = 382.5 = 380 J (2 SF)

Q = sm∆T ; ∆T = Q/ sm; ∆T = Tf – Ti; Tf = ∆T + Ti ∆T = 1000. J Case 2 – If two objects absorb the exact same amount of heat energy in joules, will they be at same final temperature? Q = sm∆T ; ∆T = Q/ sm; ∆T = Tf – Ti; Tf = ∆T + Ti ∆T = 1000. J Silver =434.7= 430 (2 SF) (0.23 J/ g oC)( 10.0 g) Tf = ∆T + Ti; Tf = 430 + 25 = 455 oC Steel: ∆T = 1000. J (0.51 J/g oC) (10.0 g) = 196 = 200 (2 SF) Different s values causes different ∆T Tf = ∆T + Ti; Tf = 200 + 25 = 225 oC

Analogy to Case #1: Is the same energy required to lift a bowling ball and ping ball to the same height? Energy required to move each objective is analogous to heat added Arrows are analogous to force (energy) required to lift Height difference is analogous to ∆T 10 pounds 1/1760 of a pound Different masses analogous to different specific heat capacity

Analogy to Case #2: If the same energy is applied to the bowling ball and ping ball will they rise to the same height? = Force = Energy required to move each objective is analogous to heat added Height difference is analogous to ∆T 10 pounds 1/1760 of a pound Different masses analogous to different specific heat capacity