[{"data":1,"prerenderedAt":73},["ShallowReactive",2],{"q-fire-106-1-fire-science-027":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-106-1-火災學概要-027","fire-106-1-fire-science-027",106,1,27,"要使 1 kg 之乙炔完全燃燒，在標準狀態下，其所需之空氣容積為多少？",{"A":16,"B":17,"C":18,"D":19},"7.82 m3","8.34 m3","10.26 m3","9.62 m3","C",null,[],false,"本題考點：可燃氣體完全燃燒的理論空氣量計算，核心是化學計量配平加上亞佛加厥定律的莫耳體積換算。\n【正解理由】依乙炔完全燃燒反應式 C₂H₂＋2.5O₂→2CO₂＋H₂O，每 1 莫耳乙炔需 2.5 莫耳氧氣；空氣含氧體積比 21%，標準狀態下 1 莫耳氣體佔 22.4 L，換算得所需空氣約 10.26 m³，故選 C。\n【逐項排除】\n(A) 7.82 m³：相當於氧的化學計量係數誤取約 1.9，配平不足而低估空氣量。\n(B) 8.34 m³：相當於誤配成 C₂H₂＋2O₂，係數由 2.5 掉成 2，最常見的配平錯誤。\n(C) 10.26 m³：以係數 2.5、含氧體積比 21%、莫耳體積 22.4 L 算得，為正解。\n(D) 9.62 m³：相當於誤用質量含氧率 23% 取代體積比 21%，分母偏大使結果偏小。\n【演算步驟】乙炔分子量 M＝12×2＋1×2＝26 g\u002Fmol；n(C₂H₂)＝1000 g÷26 g\u002Fmol＝38.46 mol；依配平 n(O₂)＝38.46 mol×2.5＝96.15 mol；理論空氣莫耳數 n(air)＝96.15 mol÷0.21＝457.9 mol；標準狀態體積 V＝457.9 mol×22.4 L\u002Fmol＝10257 L＝10.26 m³。\n【記憶點】先配平抓 2.5 倍氧，再除以 0.21、乘以 22.4，三步到底。","理論空氣量的計算骨幹只有三個環節：配平取得氧的化學計量係數、以空氣含氧體積比 21% 把氧量放大成空氣量、再用標準狀態莫耳體積 22.4 L\u002Fmol 換成體積。碳氫化合物 C_xH_y 的通式為 C_xH_y＋(x＋y\u002F4)O₂→xCO₂＋(y\u002F2)H₂O，乙炔代入 x＝2、y＝2 即得 2＋0.5＝2.5，這個通式能省去每題重新配平的時間，甲烷（x＝1,y＝4）得 2、丙烷（x＝3,y＝8）得 5、丁烷得 6.5，都可直接套用。\n單位與常數要分清：22.4 L\u002Fmol 是標準狀態（0℃、1 atm）的莫耳體積，若題目改給常溫常壓（25℃）則應改用約 24.5 L\u002Fmol，答案會相差約 9%，這是命題者最愛設的陷阱。空氣含氧量亦有兩套數字，體積百分比 21%、質量百分比約 23%，計算「體積」時必須用 21%，計算「質量」時才用 23%，混用即落入本題 (D) 的誘答。\n此一數值與燃燒界限（爆炸範圍）互為表裡。乙炔的燃燒範圍極寬，約 2.5% 至 80% 以上，且分子內含三鍵、屬吸熱化合物，即使無氧亦可能因壓縮或衝擊而分解爆炸，因此其乙炔氣瓶內以丙酮吸附於多孔物質中儲存，並列為公共危險物品法規管制的可燃性高壓氣體。理論空氣量除以燃料量所得的空氣燃料比，可再導出理論混合比與化學計量濃度 Cst＝100\u002F(1＋4.773×(x＋y\u002F4))，並以勒沙特列公式處理混合氣體的燃燒下限，這條線是火災學計算題的主軸之一。\n延伸考法包括：改問理論氧氣量（不除 0.21）、改問實際空氣量（乘以過剩空氣係數 m）、改問燃燒生成的二氧化碳體積或水蒸氣量、或要求以質量而非體積作答。只要先把配平係數寫對，其餘都是乘除法的排列組合。",true,[28,32,36,40,44,48],{"webId":29,"stem":30,"number":31,"year":11,"session":12},"fire-106-1-fire-science-026","有一家用延長線，欲連接電子鍋、熱水瓶及微波爐，耗電功率分別為 550 W、1100 W 及 2200 W，請問該延長線至少應具多大之容許電流？（家用電壓為 110 V）",26,{"webId":33,"stem":34,"number":35,"year":11,"session":12},"fire-106-1-fire-science-028","有一平板絕緣層內面溫度為 270℃，外面以熱對流方式散失到 20℃的空氣中，平板厚度為 4 cm，熱傳導係數 K=1.2W\u002Fm℃，若要使平面外面的溫度不超過 70℃，試求其對流熱傳係數的極小值？",28,{"webId":37,"stem":38,"number":39,"year":11,"session":12},"fire-106-1-fire-science-025","依據實驗，人穿著普通作業服時，其受熱之界限值約為多少？",25,{"webId":41,"stem":42,"number":43,"year":11,"session":12},"fire-106-1-fire-science-029","一般而言，區劃空間火災中引發閃燃時，樓地板最低輻射熱通量值約為何？",29,{"webId":45,"stem":46,"number":47,"year":11,"session":12},"fire-106-1-fire-science-024","假設正向煙囪效應在中性帶以上 8 m 處的壓差為 10 Pa，若建築物內、外的溫差不變，中性帶以上 20 m 處的壓差為多少？",24,{"webId":49,"stem":50,"number":51,"year":11,"session":12},"fire-106-1-fire-science-030","依照 McCaffrey 火羽流理論，下列何者正確？",30,[53,57,61,65,69],{"webId":54,"year":55,"stem":56,"number":13},"fire-113-1-fire-science-027",113,"火災發生後至閃燃發生的時間稱為閃燃時間（F.O.T.），影響閃燃時間的重要因素，下列何者錯誤？",{"webId":58,"year":59,"stem":60,"number":13},"fire-112-1-fire-science-027",112,"下列何種措施於室內發生火災時有助於防止或延緩閃燃的發生？",{"webId":62,"year":63,"stem":64,"number":13},"fire-111-1-fire-science-027",111,"下列關於乙炔的敘述，何者錯誤？",{"webId":66,"year":67,"stem":68,"number":13},"fire-110-1-fire-science-027",110,"某建築物的插座電壓為 110 伏特，在其延長線上的插座同時插 880 瓦的電磁爐、110 瓦的電風扇及 1100 瓦的電熱器，請問該延長線之額定電流至少需多少安培？",{"webId":70,"year":71,"stem":72,"number":13},"fire-109-1-fire-science-027",109,"下列有關泡沫滅火劑，何者敘述正確？",1785129968084]