\(2Zn+O_2\underrightarrow{t^o}2ZnO\)

\(n_{Zn}=\frac{32,5}{65}=0,5\left(mol\right)\)

\(n_{ZnO}=n_{Zn}=0,5\left(mol\right)\)

\(m_{ZnO}=0,5.81=40,5\left(g\right)\)

\(n_{O_2}=\frac{1}{2}.n_{Zn}=\frac{1}{2}.0,5=0,25\left(mol\right)\)

\(V_{O_2}=0,25.22,4=5,6\left(l\right)\)

3/4 + 1/4 : x  = 2/5 

=> 1/4 : x = 2/5 - 3/4 

=> 1/4 : x = -7/20

=> x = 1/4 : (-7/20)

=> x = -5/7

4P+5O₂=t^o=>2P₂O₅

\(n_P=\frac{6,2}{31}=0,2\left(mol\right);n_{O_2}=\frac{6,72}{22,4}=0,3\left(mol\right)\)

Theo PTHH, ta có: \(\frac{0,2}{4}< \frac{0,3}{5}\)=>O₂ dư

\(n_{O_2\left(dư\right)}=0,3-\left(\frac{0,2.5}{4}\right)=0,05\left(mol\right)\)

\(m_{O_2\left(dư\right)}=0,05.32=1,6\left(g\right)\)

\(n_{P_2O_5}=\frac{2}{4}.n_P=\frac{2}{4}.0,2=0,1\left(mol\right)\)

\(m_{P_2O_5}=0,1.142=14,2\left(g\right)\)

a) 4P+5O₂=t^o=>2P₂O₅

b) \(n_P=\frac{31}{31}=1\left(mol\right);n_{O_2}=\frac{32}{32}=1\left(mol\right)\)

Theo PTHH: Vì: \(\frac{1}{4}>\frac{1}{5}\)=>P dư

\(n_{P\left(dư\right)}=1-\left(\frac{1.4}{5}\right)=0,2\left(mol\right)\)

\(m_{P\left(dư\right)}=0,2.31=6,2\left(g\right)\)

\(n_{P_2O_5}=\frac{2}{5}.n_{O_2}=\frac{2}{5}.1=0,4\left(mol\right)\)

\(m_{P_2O_5}=0,4.142=56,8\left(g\right)\)

2Cu+O₂=t^o=>2CuO

\(n_{CuO}=\frac{8}{80}=0,1\left(mol\right)\)

\(m_{Cu}=n_{Cu}.64\Leftrightarrow n_{CuO}.64=0,1.64=6,4\left(g\right)\)

\(n_{O_2}=\frac{1}{2}.n_{Cu}=\frac{1}{2}.0,1=0,05mol\)

\(V_{O_2}=0,05.22,4=1,12l\)

b) 2KMnO₄-np-->K₂MnO₄+MnO₂+O₂

\(n_{KMnO_4}=2.n_{O_2}=2.0,05=0,1\left(mol\right)\)

\(m_{KMnO_4}=0,1.158=15,8\left(g\right)\)

Dear Josie
Thank you very much for your last letter. It was great to hear about your holiday in Cornwall. But I was sorry to hear that the wea ther was so bad.
Everything is going well here. My course is interesting and I’ve met a lot of nice people. The other students are very friendly. The most exciting thing is the drama group. I joined it last month and I’m really enjoying it. We’re going to do a play at the and of term and I’m going to have one of the main parts. A TV company is making a film about the university and they are going to film the show. Yes, your little sister is going to be famous.
Write soon and give my love to Mum and Dad.
Love,
Victoria

Dễ thấy ABC là tam gác vuông

Theo đề ...................., ta có ABDC là HCN

=> S=15.20=300cm²