[DSE化學2019]同學準備好DSE CHEM未?

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153 Like 27 Dislike
2019-02-18 23:37:03
通常題目本身會指定你基於咩aspect去衡量優次
的確係有energy produced per mass of fuel呢個reason
過往AL亦試過比數據你計enthalpy再比較
2019-02-18 23:39:39
巴打 想問返2018年Paper2 分辨K2SO4 and K2SO3個題
想問用K2Cr2O7/H+ 可以嗎? Marking無寫到 唔知自己啱唔啱
2019-02-18 23:45:26
可以
2019-02-18 23:46:34
咁其實係點推到出黎
e.g. gasohol同ethanol比較 點解gasohol既energy density>ethanol
唔想死背
2019-02-19 00:09:40
如果你咁specific兩隻fuel就要有數據黎計
你講呢個case可以睇下AL 2005 P2 Q5(a)
會用data計出黎prove
2019-02-19 00:31:40
姐係冇一個特定既trend(increase with more no. of c個啲) 如果要用就要當係factual既野背左佢?
我意思係答state an advantage of xx against yy (兩隻fuel)咁樣既題目
2019-02-19 00:53:23
淨係計energy density of hydrocarbons(唔計combustion所需既O2 mass)
通常少d C既CxHy energy density會高d
如果有埋O 即係CxHyOz果d 就會無一個consistent既正比關係
而且一隻fuel唔係睇energy density咁簡單
仲要考慮咩佢要用幾多oxidizing agent (最common係O2)
易唔易complete combustion (唔complete會釋放唔曬能量)
octane value辛烷值 (anti knocking)
當然仲有cost
所以你無實際數據既話唔好亂估
一係諗下storage / safety / pollution呢幾方面比較明確d既方向
2019-02-19 22:29:19
Tollen’s reagent + aldehyde 係咪一定要place the reaction mixture in a beaker of warm water做?點解?
另外,如果evaporate the reaction mixture to dryness,點解explosion may occur ?
2019-02-19 23:09:00
source ?
2019-02-19 23:59:37
yes 因為ZnO屬於amphoteric oxide (似Al2O3)
2019-02-20 00:02:35
HKALE 1994 Paper 1 4(b)
2019-02-20 00:06:50
generally會用water bath微熱
dry左會form silver nitride Ag3N 會explosive
2019-02-20 00:39:44
唔該巴打!
2019-02-20 02:09:33
想問下巴打
如果題目問 What is Hess Law
咁應該要答咩?
2019-02-20 02:11:32
definition
The overall enthalpy change of a reaction is independent of the reaction pathway.
2019-02-20 07:28:24
oh 原來係問緊同一樣野
2019-02-20 18:27:15
想問下如果比較啲simple molecular structure 嘅element 同gp 0嘅element ,e.g. O2 and Ne
咁答molecular size of o2>molecular size of Ne , van der waals force between O2 molecules is greater than van der waals force between Ne atoms 定Ne molecules
2019-02-20 20:15:12
yes
2019-02-20 21:04:31
但應該寫between Ne atoms 定 Ne molecules?定兩個都啱
2019-02-20 21:05:59
Ne molecules
因為Ne呢種情況叫mono-atomic molecule
2019-02-20 21:30:06
原則上寫atom定molecule都無所謂 因為佢本質上可定義為atom or molecule (monatomic)
當然如果describe緊molecule既behavior 我自己傾向寫返molecule
2019-02-21 20:36:41
solid Na2Co3 會5會dissolve in NaCl solution
2019-02-21 22:14:01
點解唔會?
2019-02-22 00:12:59
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