請問這數怎做

比熱容是每單位質量物質的熱容量．．．（specific heat capacity）單位應該不是Ｊ．．．而是Ｊ／ｋｇ／ｋ或者Ｊ／ｋｇ／Ｃ （Ｃ＝degree celsius）
煤燃燒放出的熱量的20%被吸收，被什麼吸收？（就當是我中文太差，理解不了題目吧．我寫了兩個不同的答案．．．你選適合的那一個就可以）

如果是有８０％熱量是用來燒水的話：
c (water) = 4200 J / kg / C
c (aluminium) = 0.88 * 10^3 = 880 J / kg / C

Energy needed to boil the water = mc (water) * change in temperature
= 5 * 4200 * (100 - 20) = 1.68 * 10^6 J
Energy needed to heat the aluminium container = mc (aluminium) * change in temperature
= 0.5 * 880 * (100-20) = 3.52 * 10^4 J
Total energy needed = 1.68 * 10^6 + 3.52 * 10^4 = 1.715 * 10^6 J
Energy provided by 1 kg of coal which can heat up the water = 3.4 * 10^7 * (1-20%)
= 2.72 * 10^7 J
Amount of coal needed = Total energy needed / Energy provided by 1 kg of coal which can heat up the water
= 1.715 * 10^6 / 2.72 * 10^7
= 0.0631 kg

如果是只有２０％熱量是用來燒水的話：
c (water) = 4200 J / kg / C
c (aluminium) = 0.88 * 10^3 = 880 J / kg / C

Energy needed to boil the water = mc (water) * change in temperature
= 5 * 4200 * (100 - 20) = 1.68 * 10^6 J
Energy needed to heat the aluminium container = mc (aluminium) * change in temperature
= 0.5 * 880 * (100-20) = 3.52 * 10^4 J
Total energy needed = 1.68 * 10^6 + 3.52 * 10^4 = 1.715 * 10^6 J
Energy provided by 1 kg of coal which can heat up the water = 3.4 * 10^7 * 20%
= 6.8 * 10^6 J
Amount of coal needed = Total energy needed / Energy provided by 1 kg of coal which can heat up the water
= 1.715 * 10^6 / 6.8 * 10^6
= 0.2522 kg

將水燒開 即鋁壺及水同時到達攝氏100度

m1:鋁壺質量 c1:鋁比熱容 m2:水的質量 c2:水比熱容(4200J)


E=m1c1(T1-T2)+m2c2(T1-T2)
E=(0.5*0.88*10^3+5*4200)(100-20)
E=1715200J
至少要燒多少無煙煤:
m*(3.4*10^7)*20%=1715200
m=0.2522kg

2006-12-01 14:48:12 補充：
準備至四位小數

2006-12-01 14:48:32 補充：
準確至四位小數