Term 1-Chemistry讨论区

weston123453

1.why nitrogen dioxide dimerise to form dinitrogen tetroxide?

2.both ethyne and nitrogen hav triple bond,which one more reactive.explain.

weesiewwen

这题怎么做？
The decomposition of a compound A into its products is a zero order reaction. The rate constant at 380K is 0.083 moldm-3min-1 and the initial concentration of A is 3.50 moldm-3.
(a) Calculate the concentration of A after 10 minutes.
(b) How long will it take for the concentration of A to drop to 1.00 moldm-3?

justin96

ethanol and iodoethane , discuss solubility of this 2 compound , 求答案

lollylolly

justin96 发表于 7-8-2014 12:03 AM
ethanol and iodoethane , discuss solubility of this 2 compound , 求答案

Ethanol 是一种 alcohol. 它可以 form hydrogen bond with water molecule.
Iodoethane 是 alkane. Hydrogen bond 不能 form within iodoethane and water molecule. Iodoethane 和 water molecule 之间只有 weak intermolecular force.
所以 ethanol is more soluble.

lollylolly

weesiewwen 发表于 3-8-2014 12:16 PM
这题怎么做？
The decomposition of a compound A into its products is a zero order reaction. The rate ...

(a) For zero order reaction, r=k.
k= 0.083 mol dm-3 min -1
[At] = -kt + [A0]
= -(0.083 x 10) + 3.50
=2.67 mol dm-3.

(b) [At] = -kt + [A0]
1.00 = -(0.083)(t) + 3.50
t = 30 minutes

weesiewwen

determine the pH of 25cm3, 0.125 moldm-3 HNO3 solution.怎么算？

lollylolly

weesiewwen 发表于 13-8-2014 03:05 PM
determine the pH of 25cm3, 0.125 moldm-3 HNO3 solution.怎么算？

HNO3 --> H+ + NO3-

[H+] = [HNO3]
= 0.125 x (25/1000)
= 3.125 x 10-3 M

pH= -log[H+]
= -log (3.125 x 10-3)
= 2.51

HNO3 是 strong acid, 它可以dissociate completely to form H+ ion

weesiewwen

calculate the pH of 1.0x10-8 moldm-3 HCl.这个怎么算？ （答案：6.98）

weesiewwen

in a titration of 20cm3 of 0.1 moldm-3 HNO3 with 0.1 moldm-3 NaOH, what is the pH after 10cm3 of NaOH solution has been added??怎么做？？

MichelleLow

Help to solve this question:-
A 2.5 dm^3 vessel contains 16.0g of oxygen at 300K.The mixture is continously sparked and then allowed to cool to 300 K. What is the final pressure of the system? State any assumption you made in your calculations.

ngaikc21

试着做了一下

参考网页http://www.thebigger.com/chemist ... e-ph-of-10-8-m-hcl/

ngaikc21

weesiewwen 发表于 16-8-2014 03:20 PM
in a titration of 20cm3 of 0.1 moldm-3 HNO3 with 0.1 moldm-3 NaOH, what is the pH after 10cm3 of NaO ...

试着做了一下

求答案

ngaikc21

MichelleLow 发表于 28-8-2014 07:59 PM
Help to solve this question:-
A 2.5 dm^3 vessel contains 16.0g of oxygen at 300K.The mixture is con ...

如果题目没理解错的话
就这样

订正a改去KPa

ngaikc21

weesiewwen 发表于 13-8-2014 03:05 PM
determine the pH of 25cm3, 0.125 moldm-3 HNO3 solution.怎么算？

就
pH=-log [H+]
    =-log [0.125]
    =0.90
我觉得那个volume好像用不着

kervinwhz

为什么I3是linear?:Q

ngaikc21

kervinwhz 发表于 3-9-2014 10:11 AM
为什么I3是linear?:Q

因为中心粒子I有五个electron pairs(2bonding pairs &3lone pairs).     based on valence shell electron-pair repulsion theory I3是属 trigonal bipyramidal 里的linear shape
参考VSEPR 和Lewis structure of I3  
              

Cheeyan0530

Chemistry chp 4
可以解释一下 Maxwell-Boltzmann Distribution Curve吗？


#求助

doeramon

Cheeyan0530 发表于 8-9-2014 04:16 PM
Chemistry chp 4
可以解释一下 Maxwell-Boltzmann Distribution Curve吗？

你可以把它当成考试的分
y-axis学生人数 ，x-axis 考试分数
拿到低分的人很少，大多数都拿到高分，很少人拿高分

如果拿低分和高分的人提高，中等分就会比刚才低,curve就会向右移动

明白吗？我老师就是这样解释，我才明白的

Cheeyan0530

Chp 6B

我不明白Arrhenius theory...
它跟bronsted Lowry theory和Lewis Theory有什么分别？

#求助

MichelleLow

Cheeyan0530 发表于 22-9-2014 07:20 PM
Chp 6B

我不明白Arrhenius theory...

用acid 来看， for arrhenius theory: the acid dissolve in water to produce H+ (look at water)
                          Bronsted-Lowry : the acid donate proton(H+)  (look at proton)
                            Lewis : the acid accept electron pair to form dative bond (look at electron pair)
就这样分别咯~你读它们的意思已经很明显了。