[{"data":1,"prerenderedAt":72},["ShallowReactive",2],{"q-fire-112-1-fire-science-039":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-112-1-火災學概要-039","fire-112-1-fire-science-039",112,1,39,"假設定量乙醇(C2H5OH)與理論空氣量混合後產生完全燃燒，其後將燃燒廢氣冷卻至常溫，則其中二氧化碳的濃度約為多少%？",{"A":16,"B":17,"C":18,"D":19},"12.3","14.0","15.1","16.2","C",null,[],false,"本題考點：完全燃燒的化學計量與乾燥燃燒廢氣中二氧化碳濃度的計算。\n【正解理由】乙醇完全燃燒式為 C2H5OH＋3O2 → 2CO2＋3H2O。理論空氣量以氧佔 21%、氮佔 79% 計，需氧 3 莫耳時伴隨氮 3×(79／21)＝11.29 莫耳。廢氣冷卻至常溫後 3 莫耳水蒸氣凝結為液態而退出氣相，乾燥廢氣為 CO2 2 莫耳與 N2 11.29 莫耳，合計 13.29 莫耳，二氧化碳濃度＝2÷13.29＝15.1%，故選 C。\n【逐項排除】\n(A) 12.3% 是把 3 莫耳水蒸氣一併計入氣相（2÷16.29）的濕基濃度，與冷卻至常溫的條件不符。\n(B) 14.0% 介於濕基 12.3% 與乾基 15.1% 之間，無對應的計量關係。\n(C) 正確：乾燥廢氣只計 CO2 與 N2，2÷13.29 約為 15.1%。\n(D) 16.2% 對應乾燥廢氣總量約 12.3 莫耳，較實際的 13.29 莫耳少算約 1 莫耳氮，與 79 比 21 的空氣組成不符。\n【記憶點】理論空氣量題先寫平衡式，再問水算不算：冷卻至常溫即乾基，水不計。","理論空氣量（化學計量空氣量）的計算流程固定：先寫平衡的燃燒方程式求出理論需氧莫耳數，再以空氣中氧佔 21%、氮佔 79% 換算。乙醇的完全燃燒式為 C2H5OH＋3O2 → 2CO2＋3H2O，每莫耳乙醇需氧 3 莫耳，伴隨的氮為 3×(79／21)＝11.29 莫耳，理論空氣量即 3×(100／21)＝14.29 莫耳。換算為質量基時，14.29 莫耳空氣約 414 公克，除以乙醇分子量 46 公克，得每公斤乙醇約需 9 公斤空氣，這個數量級可用來快速檢核計算是否合理。\n燃燒廢氣的組成有濕基與乾基兩種表示法，這是本題的關鍵分歧點。廢氣在高溫時水以蒸氣存在，總莫耳數為 2＋3＋11.29＝16.29，二氧化碳的濕基濃度為 12.3%；冷卻至常溫後水蒸氣凝結成液態而退出氣相，乾燥廢氣僅剩 2＋11.29＝13.29 莫耳，二氧化碳濃度提高為 15.1%。題幹寫「冷卻至常溫」即指定以乾基計算。\n這個「理論最大二氧化碳濃度」是燃料的特徵值，可用於推估燃燒的完全程度。同法計算甲烷，CH4＋2O2 → CO2＋2H2O，伴隨氮為 2×(79／21)＝7.52 莫耳，乾燥廢氣 8.52 莫耳，二氧化碳乾基濃度約 11.7%；燃料中碳氫比愈高，該特徵值愈大。\n易混淆概念對照：實際空氣量與理論空氣量之比為空氣比（過剩空氣係數），其超出一的部分即過剩空氣率，實際燃燒必有過剩空氣，會把二氧化碳濃度稀釋到理論值以下；供氣不足時則生成一氧化碳，二氧化碳濃度同樣下降，因此量測值恆低於理論值。延伸考點包括各種燃料理論空氣量與理論廢氣量的計算，以及由廢氣中氧濃度反推空氣比。",true,[28,32,36,40,44,48],{"webId":29,"stem":30,"number":31,"year":11,"session":12},"fire-112-1-fire-science-038","當外部風的風向不變而風速加倍時，對處於煙囪效應下的大樓而言，下列敘述何者正確？",38,{"webId":33,"stem":34,"number":35,"year":11,"session":12},"fire-112-1-fire-science-040","已知距離光源 2 公尺處的減光率為 20%，則當與光源的距離加倍時，其減光率約為多少%？（提示：log(80)≒ 1.903，log(64)≒ 1.806）",40,{"webId":37,"stem":38,"number":39,"year":11,"session":12},"fire-112-1-fire-science-037","升高環境溫度對於環氧乙烷的分解爆炸有何影響？",37,{"webId":41,"stem":42,"number":12,"year":43,"session":12},"fire-113-1-fire-science-001","有一倉庫長寬高分別為 8 公尺，5 公尺及 4 公尺，內置可燃物之總重量為 600 公斤，試計算該倉庫之火載量若干（kg\u002Fm2）？",113,{"webId":45,"stem":46,"number":47,"year":11,"session":12},"fire-112-1-fire-science-036","下列那一種措施有助於提高粉塵爆炸的防護作用以增加其安全性？",36,{"webId":49,"stem":50,"number":51,"year":43,"session":12},"fire-113-1-fire-science-002","建築物為防止火焰透過大樓窗口向上層延燒，下列敘述何者正確？",2,[53,56,60,64,68],{"webId":54,"year":43,"stem":55,"number":13},"fire-113-1-fire-science-039","有關於液化石油氣之性質與事故發生之處置原則，下列敘述何者錯誤？",{"webId":57,"year":58,"stem":59,"number":13},"fire-111-1-fire-science-039",111,"撕下新購的電視機螢幕保護封膜時遭受靜電，其原因為下列何者？",{"webId":61,"year":62,"stem":63,"number":13},"fire-110-1-fire-science-039",110,"某建築物內部的空氣溫度為 27 ℃，發生火災的房間溫度為 627 ℃，流入該起火房間的空氣體積流量為 4 m3\u002Fs，若忽略燃燒熱分解過程而產生的質量流率，請計算流出起火房間的煙霧體積流量約為多少？",{"webId":65,"year":66,"stem":67,"number":13},"fire-109-1-fire-science-039",109,"帶電物體或其附近之接地體，有突出部分或刃狀部分時，在該等前端近旁，所出現之微弱發光放電，此現象稱為？",{"webId":69,"year":70,"stem":71,"number":13},"fire-108-1-fire-science-039",108,"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？",1785129966660]