[{"data":1,"prerenderedAt":72},["ShallowReactive",2],{"q-fire-109-1-fire-science-001":3},{"subject":4,"subjectSlug":5,"subjectKicker":6,"subjectShort":7,"question":8,"related":26,"sameNumber":52,"hasEssay":25},"火災學概要","fire-science","火災學 · Fire Science","火災學",{"id":9,"webId":10,"year":11,"session":12,"subject":4,"number":12,"stem":13,"options":14,"answer":19,"answerNote":20,"images":21,"imagesPending":22,"lawTimestamp":11,"explanation":23,"explanationDeep":24,"freq":12,"indexable":25},"fire-109-1-火災學概要-001","fire-109-1-fire-science-001",109,1,"已知辛烷的燃燒下限為 0.92（vol%），根據 Burgess-Wheeler 定理其燃燒熱約為多少？",{"A":15,"B":16,"C":17,"D":18},"1,750 kcal\u002Fmol","1,200 kcal\u002Fmol","950 kcal\u002Fmol","750 kcal\u002Fmol 2 2 2","B",null,[],false,"本題考點：Burgess-Wheeler 定則——燃燒下限與燃燒熱之乘積約為定值。\n【正解理由】Burgess-Wheeler 定則指出,同系列可燃性氣體或蒸氣,其燃燒下限(以體積百分比表示)與燃燒熱(kcal\u002Fmol)之乘積接近一個常數,約 1,050 至 1,100 kcal\u002Fmol。以辛烷燃燒下限 0.92 vol% 代入:取常數 1,100 時,燃燒熱≒1,100÷0.92≒1,196 kcal\u002Fmol;即使取較保守的 1,050,亦得 1,050÷0.92≒1,141 kcal\u002Fmol。兩種取法算出的值都最貼近 1,200 kcal\u002Fmol,故選 B。\n【逐項排除】\n(A) 1,750 kcal\u002Fmol 反推燃燒下限約 1,100÷1,750≒0.63 vol%,遠低於題給的 0.92 vol%,對應的是碳數更高的物質。\n(B) 1,200 kcal\u002Fmol 與 0.92 vol% 相乘得約 1,104,正落在定則常數範圍內,為本題應選者。\n(C) 950 kcal\u002Fmol 反推燃燒下限約 1.16 vol%,高於題給值,對應的是分子較小、燃燒熱較低的物質。\n(D) 750 kcal\u002Fmol 反推燃燒下限約 1.47 vol%,偏離題給值最遠;會選此項多半是把定則的反比關係記反了。\n【記憶點】燃燒下限乘燃燒熱約等於 1,100,下限愈低、燃燒熱愈大,兩者成反比。","這個定則的物理意義比公式本身更值得懂。火焰要能自持傳播,必須把前方未燃混合氣加熱到可以持續反應的溫度;而在燃燒下限這個臨界濃度上,單位體積混合氣完全反應所釋放的熱量,恰好只夠把混合氣加熱到那個絕熱火焰溫度。由於同系列碳氫化合物的產物(二氧化碳與水)相同、混合氣主體都是空氣,單位體積所需的熱量差異不大,因此「濃度×每莫耳燃燒熱」就近似守恆。換句話說,燃燒熱愈大的分子,只要愈少的莫耳數就能湊足這份熱量,燃燒下限自然愈低。\n\n用同系物排一排就很直觀:甲烷燃燒下限約 5.0 vol%、乙烷約 3.0%、丙烷約 2.1%、丁烷約 1.8%,到辛烷已降至約 0.9%;而燃燒熱則沿著碳數一路遞增。兩邊相乘,結果都落在一千出頭。忘了常數可用甲烷回推:甲烷燃燒熱約 210 kcal\u002Fmol,5.0×210≒1,050。\n\n單位換算順手記:1 kcal＝4.186 kJ,所以 1,200 kcal\u002Fmol≒5,023 kJ\u002Fmol;若題目改用 kJ\u002Fmol 出,常數就變成約 4,400 至 4,600 kJ\u002Fmol,換算比記兩套數字安全。\n\n最容易與本定則混淆的是勒沙特列(Le Chatelier)公式:混合氣體之燃燒下限 L＝100÷Σ(Vi\u002FLi),其中 Vi 為各成分在可燃氣中所占體積百分比、Li 為各成分之燃燒下限。兩者的分工是——勒沙特列處理「多種可燃氣混合後的下限是多少」,Burgess-Wheeler 處理「單一物質的下限與其燃燒熱有何關係」。題幹只要出現「混合氣體」「各占多少%」就走勒沙特列,出現「燃燒熱」「約為多少 kcal\u002Fmol」就走 Burgess-Wheeler。\n\n延伸考點還有兩個方向:一是 Jones 法則,以化學計量濃度 Cst 估算,燃燒下限約 0.55Cst、燃燒上限約 3.5Cst,可與本定則互相驗算;二是溫度與壓力對燃燒範圍的影響——溫度升高時分子動能增加,下限下降、上限上升,燃燒範圍變寬,這也是為什麼同一物質在火場高溫下遠比常溫危險。作答計算題時務必確認題目給的下限是體積百分比,若給的是 g\u002Fm³ 之類的質量濃度,必須先換算成 vol% 才能代入。",true,[27,32,36,40,44,48],{"webId":28,"stem":29,"number":30,"year":31,"session":12},"fire-108-1-fire-science-040","建築物火災進入最盛期時，燃料數量龐大，但因對外開口相對較少的情況下，燃燒速度因開口通風量而受限，此現象稱為：",40,108,{"webId":33,"stem":34,"number":35,"year":11,"session":12},"fire-109-1-fire-science-002","三個面積分別為 0.20 m ，0.40 m ，0.60 m 之開口相互串聯時，其等效流動面積為何？",2,{"webId":37,"stem":38,"number":39,"year":31,"session":12},"fire-108-1-fire-science-039","高壓氣體的爆炸界限，通常較常壓下為廣，爆炸上限也明顯提高，但下列何種氣體之爆炸範圍及爆炸上限在高壓下卻降低？",39,{"webId":41,"stem":42,"number":43,"year":11,"session":12},"fire-109-1-fire-science-003","依用戶用電設備設置規則及建築技術規則，下列避雷設置敘述何者錯誤？",3,{"webId":45,"stem":46,"number":47,"year":31,"session":12},"fire-108-1-fire-science-038","可燃物不藉由火焰或電器火花引起燃燒，在大氣中僅因受熱而引發燃燒的最低溫度稱為：",38,{"webId":49,"stem":50,"number":51,"year":11,"session":12},"fire-109-1-fire-science-004","某一火災成長至 2,000 kW 所需時間為 400 秒，請問該火災屬何種成長性火災？[Q：釋熱率（MW）； 1\u002F2 t：經過時間（sec）；k：火災成長常數（sec\u002FMW ）]",4,[53,57,61,64,68],{"webId":54,"year":55,"stem":56,"number":12},"fire-111-1-fire-science-001",111,"近年來已有水滅火器經型式認可，下列敘述何者正確？",{"webId":58,"year":59,"stem":60,"number":12},"fire-110-1-fire-science-001",110,"下列物質各取 1 莫耳進行完全燃燒，何者所需的理論空氣量（kg）最少？",{"webId":62,"year":31,"stem":63,"number":12},"fire-108-1-fire-science-001","假設火場中只含一種燃料且均勻分布，起火後火勢循 t2 成長理論持續成長，且火災成長常數呈定值。已知起火後第 1 分鐘燒耗燃料 1 公斤，則再經 2 分鐘後，從起火開始起算總共燒耗若干公斤之燃料？",{"webId":65,"year":66,"stem":67,"number":12},"fire-107-1-fire-science-001",107,"在火場中會因吸入下列何種氣體，導致阻礙紅血球輸氧功能而造成窒息死亡？",{"webId":69,"year":70,"stem":71,"number":12},"fire-106-1-fire-science-001",106,"某物質每克的燃燒熱為 1 仟焦耳，若 100 克該物質於 10 秒內平均燃燒完，則該物質之熱釋放率為：",1785123162632]