p19_029.pdf

29. The melting point of silver is 1235K, so the temperature of the silver must ﬁrst be raised from 15 . 0 ◦ C

(=288K) to 1235K. This requires heat

Q = cm ( T f −

T i ) =(236J / kg

K)(0 . 130kg)(1235 ◦ C

−

288 ◦ C) =2 . 91

10 4 J .

Now the silver at its melting point must be melted. If L F is the heat of fusion for silver this requires

Q = mL F =(0 . 130kg)(105

10 3 J / kg) =1 . 36

10 4 J .

The total heat required is 2 . 91 × 10 4 J+1 . 36 × 10 4 J=4 . 27 × 10 4 J.