[{"data":1,"prerenderedAt":73},["ShallowReactive",2],{"q-fire-110-1-fire-science-023":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-023","fire-110-1-fire-science-023",110,1,23,"請問 2 公斤的氫氣（H2）完全燃燒，所需要的理論空氣量為多少公斤？",{"A":16,"B":17,"C":18,"D":19},"139.2","104.4","69.6","34.8","C",null,[],false,"本題考點：理論空氣量計算,由燃燒反應式的化學計量比求需氧量,再依空氣含氧率換算。\n【正解理由】完全燃燒反應式為 2H₂ + O₂ → 2H₂O,每 2 莫耳氫氣消耗 1 莫耳氧氣。氫氣分子量 2 kg\u002Fkmol,故 2 kg 恰為 1 kmol,需氧 0.5 kmol,質量 0.5 × 32 = 16 kg。空氣含氧質量分率約 23%,理論空氣量為 16 ÷ 0.23 ≈ 69.6 kg,故選 C。\n【逐項排除】\n(A) 139.2 kg:恰為正解的兩倍,係把配平誤看成一比一、需氧算成 1 kmol 即 32 kg。\n(B) 104.4 kg:對應需氧 24 kg,即誤取 0.75 kmol 氧,化學計量比不成立。\n(C) 69.6 kg:16 kg 氧除以質量含氧率 0.23 求得,正確。\n(D) 34.8 kg:恰為正解的一半,係只計入 1 kg 氫氣、或需氧誤取 8 kg 所致。\n【演算步驟】\n2H₂ + O₂ → 2H₂O;n(H₂) = 2 kg ÷ 2 kg\u002Fkmol = 1 kmol\nn(O₂) = 1 kmol × 1\u002F2 = 0.5 kmol;m(O₂) = 0.5 kmol × 32 kg\u002Fkmol = 16 kg\nA₀ = 16 kg ÷ 0.23 ≈ 69.6 kg\n【記憶點】先配平、再算氧,質量法除以 0.23、體積法除以 0.21。","理論空氣量有質量法與體積法兩條路,結果應當一致,只是取用的含氧比例不同。質量法用空氣含氧質量分率 23%(較精確為 23.2%),本題得 16 ÷ 0.23 ≈ 69.6 kg;體積法先算莫耳:0.5 kmol 氧 ÷ 0.21 ≈ 2.38 kmol 空氣,再乘空氣平均分子量 28.96 kg\u002Fkmol,得約 69 kg。兩者僅因含氧率取值的精度差異而相差不到 1%,選項刻意設計成 69.6,即是採 23% 的質量法。作答時先看選項數字落在哪一種取法,可以快速反推命題者要的算法。\n\n延伸的是空氣比(過剩空氣係數)λ 的概念:實際供氣量除以理論空氣量,λ = 1 為化學計量燃燒,λ > 1 為貧燃(過剩空氣冷卻火焰、降低溫度),λ \u003C 1 為富燃(燃料過剩、產生一氧化碳與煤煙)。建築物火災在成長期多為通風控制,λ \u003C 1,這正是室內火災大量產生一氧化碳與濃煙、造成傷亡的化學根源。\n\n氫氣本身也是常考的物質:分子量最小、擴散速度最快、燃燒界限寬達 4～75 vol%、最小引燃能量僅約 0.02 mJ(甲烷約 0.28 mJ),靜電即足以引燃,且火焰近乎無色,白晝難以目視發現。燃燒產物只有水,不生成一氧化碳與煤煙,因此不會有減光問題,但也因此不易由煙判斷火源位置。同樣的計算模式可換成甲烷(CH₄ + 2O₂)、丙烷(C₃H₈ + 5O₂),配平後套用完全相同的步驟。此外,氫氣低位發熱量約 120 MJ\u002Fkg,遠高於一般碳氫化合物,單位質量的需氧量也最大,這組數字常與理論空氣量一併出現在能量與空氣量的綜合計算題中。",true,[28,32,36,40,44,48],{"webId":29,"stem":30,"number":31,"year":11,"session":12},"fire-110-1-fire-science-022","火災中所產生的輻射熱量與下列何者成正比？",22,{"webId":33,"stem":34,"number":35,"year":11,"session":12},"fire-110-1-fire-science-024","在充足的能量下，下列何種濃度（vol%）的氫氣（H2）為燃燒界限範圍內？",24,{"webId":37,"stem":38,"number":39,"year":11,"session":12},"fire-110-1-fire-science-021","下列物質在常溫時，何者的熱傳導係數（W\u002Fm∙K）較低？",21,{"webId":41,"stem":42,"number":43,"year":11,"session":12},"fire-110-1-fire-science-025","請依據可燃性氣體完全燃燒時的化學理論濃度，計算丙烷的燃燒下限？",25,{"webId":45,"stem":46,"number":47,"year":11,"session":12},"fire-110-1-fire-science-020","某室內火場的煙層厚度為 1 公尺，若此時光學密度為 0.173，則該場域中避難反光指標之能見度為多少公尺？",20,{"webId":49,"stem":50,"number":51,"year":11,"session":12},"fire-110-1-fire-science-026","易燃性氣體受到壓縮後溫度會有升高的狀況發生，可能會發火導致火災的發生，此現象為何？",26,[53,57,61,65,69],{"webId":54,"year":55,"stem":56,"number":13},"fire-111-1-fire-science-023",111,"建築物起火後，對於防止火焰由下層窗戶往上層延燒，下列敘述何者錯誤？",{"webId":58,"year":59,"stem":60,"number":13},"fire-109-1-fire-science-023",109,"若要看清某一物體，該物體與其背景間有一定之對比度。對比度之計算：C=(B\u002FB0)-1，有關對比度下列何者正確？",{"webId":62,"year":63,"stem":64,"number":13},"fire-108-1-fire-science-023",108,"乙醇在閃火點時的飽和蒸汽壓為 25 mmHg，則乙醇在常壓下的燃燒下限約為何？",{"webId":66,"year":67,"stem":68,"number":13},"fire-107-1-fire-science-023",107,"熱傳導之熱流動方向為何？",{"webId":70,"year":71,"stem":72,"number":13},"fire-106-1-fire-science-023",106,"燃燒範圍是研判物質物性之重要因素，今有某液化石油氣，其成分為丙烷（C3H8 ）40%燃燒範圍為 2.4%~9.5%、丁烷（C4H10）60%燃燒範圍為 1.8%~8.4%，試求該液化石油氣之燃燒下限為何？",1785123162457]