ALevel化学作为一门理科课程，一直以来都是ALevel课程中的热门选择之一，目前，2022年1月ALevel化学考试时间越来越近了，大家准备的如何了？在最后阶段小编再带着大家来复习一下第一、第二单元的化学反应方程式。
第一单元
▄ Alkanes – with O2
Complete combustion：CH4+ 2O2→ CO2+ 2H2O
Incomplete combustion：CH4+ 1.5O2→CO + 2H2O
▄ Alkanes – with Cl2, UV
CH4+ Cl2→ CH3Cl + HCl
Mechanism：Photochemical free radical substitution.
▄ Alkanes – improving the quality of fuels
Catalytic Cracking：C10H22→ C5H12+ C5H10
Conditions– Heat (600oC), Al2O3
Isomerisation
Reformation
▄ Alkenes – with H2
H2C=CH2+ H2→CH3CH3
Conditions- Heat, Ni
▄ Alkenes – with Br2
CH3CH=CH2+ Br2→CH3CHBrCH2Br
Colour change (orange to colourless)
Mechanism：Electrophilic Addition
▄ Alkenes – with Bromine water
CH3CH=CH2+ Br2/ H2O →CH3CHOHCH2Br
Colour change(orange to colourless)
Mechanism：Electrophilic Addition
▄ Alkenes – with HBr/dry/gas
CH3CH=CH2+ HBr →CH3CH2BrCH3
Major product Mechanism：Electrophilic Addition
Explanation for major product：Secondary carbocationic intermediate is more stable than primary.
▄ Alkenes – with KMnO4/ H2SO4
CH3CH=CH2+ [O] →CH3CHOHCH2OH
Colour change(purple to colourless – H2SO4)
Alkenes- Polymerisation
Unit 2
▄ Group 2 metals – with H2O
Mg：Mg + H2O → MgO + H2(steam only)
Ca,Sr,Ba：Ca + 2H2O→ Ca(OH)2+ H2
▄ Group 2 metals – with O2
2Mg + O2→2MgO
▄ Group 2 metals – with Cl2
Mg + Cl2→MgCl2
▄ Group 2 Oxides – with H2O
MgO + H2O →Mg(OH)2
▄ Group 2 Oxides – with acids
MgO + H2SO4→ MgSO4+ H2O
▄ Thermal stability
❶Group 1 Carbonates：All stable to heat except for Li2CO3
❷Group 2 Carbonates：MgCO3→ MgO + CO2
❸Group 1 Nitrates
Li: 2LiNO3→ Li2O + 2NO2+ ½O2
Na, K, Rb, Cs ：NaNO3→NaNO2+ ½O2
❹Group 2 – Nitrates
Mg(NO3)2→ MgO + 2NO2+ ½O2
▄ Solubility
Group 1 and 2 Sulphates
Decreases down the group - BaSO4is insolubl
Group 1 and 2 Hydroxides
Increases down the group - Mg(OH)2is insoluble
▄ Group 7 elements – with H2O
Cl2+ H2O→HCl + HClO
▄ Group 7 elements – with NaOH
In Cold Dilute Alkali:Cl2+ 2OH-→Cl-+ ClO-+ H2O Reaction type - Disproportionation
In Hot Conc. Alkali:3Cl2+ 6OH-→ ClO3-+ 5Cl-+ 3H2O Reaction type - Disproportionation
▄ Group 7 – Displacement reactions
Cl2(g) + 2Br-(aq) → Br2(aq) + 2Cl-(aq)
Observations：Green gas → orange solution
▄ Halide ions – with conc H2SO4：
❶NaCl(s) + H2SO4→NaHSO4(s) + HCl(g)
Observations：Steamy white fumes
❷NaBr(s) + H2SO4→NaHSO4(s) + HBr(g)
2HBr(g) + H2SO4→ Br2(g) + SO2(g) + 2H2O(l)
ObservationsSteamy white fumes and orange fumes
❸NaI(s) + H2SO4→Products HI(g), I2(g) + H2S(g)
NaI(s) + H2SO4→NaHSO4(s)+HI(g)
Followed by oxidation of HI(g):
2HI(g)+H2SO4→I2(g) + SO2(g)+2H2O(l)
And:
6HI(g)+ H2SO4→3I2(g)+S(s)+4H2O(l)
And:
8HI(g)+ H2SO4→4I2(g)+ H2S(g) +4H2O(l)
Observations：Steamy white fumes and purple fumes
▄ Test for halide ions
Ag+(aq) + Cl-(aq) →AgCl(s)
Observations：White ppt – soluble in dilute ammonia
▄ Halogenoalkanes - with aqueous OH-
CH3CH2Br + OH-→ CH3CH2OH + Br-
Mechanism :Nucleophilic substitution (Sn1 or Sn2)
▄ Halogenoalkanes with ethanolic OH-
CH3CH2Br + OH-→H2C=CH2+ Br-+ H2O
Mechanism:Elimination
▄ Halogenoalkanes - with CN-
CH3CH2Br + CN-→CH3CH2CN + Br-
Mechanism:Nucleophilic substitution
▄ Halogenoalkanes - with aqueous silver nitrate
CH3CH2Br + H2O + Ag+→ CH3CH2OH + AgBr
Fastest halogenoalkane:Iodo
Explanation: C-I bond is weaker than C-Br and C-Cl
▄ Halogenoalkanes - with NH3
CH3CH2Br + NH3→CH3CH2NH2+ HBr
Conditions：Conc NH3/ heat / closed vessel
▄ Preparation of halogenoalkanes
①Chloroalkanes from alcohols :
CH3CH2OH + Cl-→ CH3CH2Cl + OH-
Conditions：H2SO4/ NaCl / heat
②Bromoalkanes from alcohols:
CH3CH2OH + Br-→CH3CH2Br + OH-
Conditions：NaBr / H3PO4/ Heat
Not H2SO4/ NaBr / heat as Br2will form
③Iodoalkanes from alcohols:
CH3CH2OH + I-→ CH3CH2I + OH-
Conditions：PI3or P / I2
Not H2SO4/ NaI / heat as I2will form
以上就是小编为大家汇总的ALevel化学中第一、二单元的化学方程式，想要申请留学的小伙伴关注起来，如果还想了解更多Alevel申请成绩、alevel真题试卷的资讯，欢迎添加我们微信kewo11，有ALevel备考指导在等您！
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