[{"data":1,"prerenderedAt":73},["ShallowReactive",2],{"q-fire-110-1-fire-science-005":3},{"subject":4,"subjectSlug":5,"subjectKicker":6,"subjectShort":7,"question":8,"related":27,"sameNumber":52,"hasEssay":26},"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":13,"stem":14,"options":15,"answer":20,"answerNote":21,"images":22,"imagesPending":23,"lawTimestamp":11,"explanation":24,"explanationDeep":25,"freq":12,"indexable":26},"fire-110-1-火災學概要-005","fire-110-1-fire-science-005",110,1,5,"已知乙烷、乙烯、乙炔的發火能量分別為 a、b、c，則 a、b、c 的大小關係為：",{"A":16,"B":17,"C":18,"D":19},"a＞b＞c","c＞b＞a","c＞a＞b","a＝b＝c","A",null,[],false,"本題考點：最小發火能量與分子結構之關係——碳氫化合物不飽和度愈高,引燃所需之最小能量愈低。\n【正解理由】乙烷為飽和烴(碳碳單鍵)、乙烯含碳碳雙鍵、乙炔含碳碳參鍵。不飽和鍵活性高,起始鏈鎖反應所需之活化能較低,故最小發火能量依序遞減:乙烷約 0.25 mJ、乙烯約 0.07 mJ、乙炔約 0.019 mJ,即 a>b>c,故選 A。\n【逐項排除】\n(A) a>b>c 即乙烷>乙烯>乙炔,與不飽和度愈高、發火能量愈低的規律一致,且符合三者實測值,為本題應選者。\n(B) c>b>a 意指乙炔最難引燃、乙烷最易引燃,與乙炔活性最高、燃燒範圍最寬(約 2.5% 至 100%)的事實相反。\n(C) c>a>b 把乙烯排在最低、乙炔排在最高,兩處排序皆與實測值不符。\n(D) a=b=c 意指三者發火能量相同,忽略了單鍵、雙鍵、參鍵在活化能上的差異,與實測值不合。\n【記憶點】愈不飽和愈易點燃:乙烷>乙烯>乙炔,發火能量一路降。","最小發火能量指在最易引燃之濃度下,以電容放電引燃可燃氣體與空氣混合氣所需之最小能量,實驗上以 E = ½CV² 計算,C 為電容量、V 為放電電壓。乙烷約 0.25 mJ、乙烯約 0.07 mJ、乙炔約 0.019 mJ,彼此相差達十倍以上;原因在於雙鍵與參鍵的鍵結較易被打斷而生成自由基,鏈鎖反應的起始門檻因此降低。\n與此規律同向的還有燃燒(爆炸)界限:乙烷約 3.0% 至 12.4%、乙烯約 2.7% 至 36%、乙炔約 2.5% 至 100%。乙炔上限達 100%,代表即使沒有空氣,受衝擊或加熱亦可能自行分解爆炸,這正是乙炔必須以丙酮溶解並填充多孔物質儲存於鋼瓶的原因,也是常見的申論素材。\n數量級感是解這類題的關鍵:一般碳氫化合物之最小發火能量約 0.2 至 0.3 mJ,氫氣、二硫化碳、乙炔則低到 0.02 mJ 附近;而人體在乾燥環境摩擦所帶靜電之放電能量可達數十毫焦耳,遠高於上述數值,可燃性氣體場所之靜電接地、防爆電氣與人員著裝規定,皆以最小發火能量為設計起點。\n易混淆對照:最小發火能量問的是「外部點火源要多少能量」,自燃點問的是「不需點火源、升到多高溫度會自行起火」,兩項指標未必同向——氫氣最小發火能量極低(約 0.02 mJ),自燃點卻高達攝氏五百度以上。答題時務必先看清問的是哪一個指標。相關考點連結:最小發火能量與燃燒界限、火焰傳播速度、消焰距離同屬描述可燃氣體易燃程度的指標群,命題常把三種二碳化合物並列比較,只要記住「乙烷、乙烯、乙炔」隨不飽和度遞增而愈危險這條主軸,大小順序題就能一次解決。",true,[28,32,36,40,44,48],{"webId":29,"stem":30,"number":31,"year":11,"session":12},"fire-110-1-fire-science-004","在氣溫 20 ℃無風的情況下，一般木造建築物形成危險界限溫度之輻射熱通量超過多少 kcal \u002F m2 h 即有延燒之危險？",4,{"webId":33,"stem":34,"number":35,"year":11,"session":12},"fire-110-1-fire-science-006","阿里山發生森林火災，已知火災當天的相對濕度為 60.0%，前一天相對濕度為 50.0%，再前一天相對濕度為 40.0%，試求火災當天的實效濕度？",6,{"webId":37,"stem":38,"number":39,"year":11,"session":12},"fire-110-1-fire-science-003","依據建築物火災的特性，當進入「穩態燃燒」階段時，釋熱率（Q）與時間（t）的關係為何？",3,{"webId":41,"stem":42,"number":43,"year":11,"session":12},"fire-110-1-fire-science-007","己烷在閃火點時的飽和蒸氣壓為 9.12 mmHg，根據 Burgess-Wheeler 定理其燃燒熱約為多少 kcal\u002Fmole？",7,{"webId":45,"stem":46,"number":47,"year":11,"session":12},"fire-110-1-fire-science-002","依據建築物火災 t2 成長理論，當釋熱率（Q）達到 4 MW 時，需要 300 秒的時間，表示火災成長之速度為下列何者？",2,{"webId":49,"stem":50,"number":51,"year":11,"session":12},"fire-110-1-fire-science-008","根據美國防火協會危險物品標示規定，將危險類別記載於菱形方塊上，其中「有害健康毒性」以何種顏色表示？",8,[53,57,61,65,69],{"webId":54,"year":55,"stem":56,"number":13},"fire-111-1-fire-science-005",111,"在苯中置入油酸鎂等金屬鹼，係採取下列何種防止靜電發生的方法？",{"webId":58,"year":59,"stem":60,"number":13},"fire-109-1-fire-science-005",109,"下列有關二氧化碳（CO2）滅火劑之敘述，何者錯誤？",{"webId":62,"year":63,"stem":64,"number":13},"fire-108-1-fire-science-005",108,"可燃性液體的閃火點（flash point），是指當其表面蒸氣與空氣混合達燃燒下限時的：",{"webId":66,"year":67,"stem":68,"number":13},"fire-107-1-fire-science-005",107,"根據美國防火協會危險物品表示規定，將危險類別記載於菱形方塊上，其中黃色表示何種危害？",{"webId":70,"year":71,"stem":72,"number":13},"fire-106-1-fire-science-005",106,"下列形成火災原因中，何者屬於硬體設備之因素？",1785123162257]