Modelová Otázka ID 2765 - 
Určete hmotnost vody, která vznikla při dokonalém spalování 15 g ethylenu.
Správná odpověď je: C
Rovnice spalování ethylenu vypadá takto:
C2H4 + 3 O2 → 2 CO2 + 2 H2O.
1 mol ethylenu (= ethenu) odpovídá 2 molům vody. Princip výpočtu je stejný jako v předchozím příkladu. Molární hmotnost ethylenu je 28 g/mol, molární hmotnost vody je 18 g/mol. Výpočet provedeme následovně:
m(voda) = n(voda) · M(voda) = 2 · [m(ethylen)/M(ethylen)] · M(voda)
m(voda) = 2 · (15/28) · 18 = 19,3 g.
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