[DSE化學2018]同學準備好DSE CHEM未? (2)

計個C
C2H6O -> C2H4O2
ON of each C : -2 -> 0 (total +4)

CaSO4 considered not soluble in water

yes CaSO4 當唔溶水(solubility rules)
Ca(OH)2 slightly soluble (slaked lime, dissolve in water to form lime water)

實際知識同考試知識既分別
其實兩隻野個solubility係一樣

H2可以由steam reform of natural gas或electrolysis of brine獲得
natural gas會係traditional method同relatively low cost
electrolysis係比較modern method 要用電所以require clean method for generating electricity (e.g. 風力)先至好

https://img.eservice-hk.net/upload/2018/03/31/173829_b8af494f9efae90f6b2992ba06c1691a.png
想問5
Ans係C
但唔係應該睇mol數咩?mol數愈多反應得愈多
咁溫度就會上升多啲 唔係咩?

H2O mol多代表放熱多 但唔代表溫度一定升得多 因為要睇埋杯溶液個總體積

例如
1M 10cm HCl + 1M 10cm NaOH
vs
1M 20cm HCl + 1M 20cm NaOH
雖然放熱量多一倍 但會因為總體積都大一倍而抵消返多左既熱 兩次實驗最後個溫度升幅會相同

簡單講就要用 H2O生成量/總體積去做比較

Thanks

巴打介唔介意用英文講番次條題目點解

mole of H2O formed by neutralization 愈多 代表heat release會大(enthalpy) 但唔代表個temperature rise一定大d 因爲total volume of reaction mixture都會影響個T

如果heat release多一倍 但同時total volume都大一倍 所以兩個factor會cancel out each other

最簡單既方法係用 H2O yield / total V of mixture

佢題目果4個case:
H2O yield: 50 , 25 , 50 , 100 (比較only 唔洗除1000)
total V: 50 , 50 , 100 , 100

所以50/50 , 25/50, 50/100 , 100/100
q=r < p=s

thanks

想問2015條返滳定
Step2 話HCl吸收所有NH3
點解HCl一定係excess
唔可以係HCl mol=NH3 mol?

出黎果d NH3 gas黎 無辦法好似滴定咁控制到啱啱好

明了

Reflux 要寫埋
H+ H3O+ 是但你

esterification要reflux
H+同H3O+同一樣野黎

heat ok

係呀

聽講heat都照寫reflux無問題
係咪真