Chemistry Question

[twin]

Originally Posted by Cheryl_pink

Nitrogen monoxide reacts spontaneously with oxygen according to the equation
2NO (g) + O2 (g) --------> 2NO2 (g)
In an experiment, 50cm3 of nitrogen monoxide was mixed with 100cm3 of oxygen.
Calculate the total volume of the gaseous mixture produced after the reaction.
Assume that the volumes of gases are measured at s.t.p.

Answer:
From the equation,
2 mol NO + 1 mol O2 ---------> 2 mol NO2
Hence, 50cm3 of NO reacts with 25cm3 of O2 to produce 50cm3 of NO2
Total volume = Volume of oxygen remaining + Volume of NO2 produced
= (100 ? 25) + 50
= 125cm3

How to get 25cm3 of O2 ???

Its a matter of ratio/mole. they gave u 100cm3 of oxygen and 50cm3 of NO. All 50 cm3 of NO can only react with maximum 25cm3 oxygen. 75cm3 of oxygen is in excess.

So sorry this description may not be sufficient. I did a solution in table form but then realised it couldnt be pasted here =/ I'm sure many others will help u.

It's so hard to put chemistry in words! lol. for me at least.

[Cheryl_pink]

So does it mean that
2 : 1
50 : 25 ??

[markwongsk]

Originally Posted by Cheryl_pink

So does it mean that
2 : 1
50 : 25 ??

Think of it this way:

For the sake of an example, assume that I give you a recipe to bake cakes. You need 2 eggs and 1 teaspoon of sugar to bake 2 cakes.

Now, if I give you x eggs, how many teaspoon of sugar do you need to ensure none of the eggs are wasted?

In chemistry terms, 2NO + O2 = 2NO2

Since you know you have 50 cm^3 of NO, (ie, x eggs), you need 25 cm^3 of O^2 (ie, x/2 sugar). In this case, we say that NO is the limiting reagent and O2 is in excess.

Let's try a different question:

Say I have 30 g of NO and 8 g of O2, which reagent is limiting and which is in excess?

30 g corresponds to 30/(14+16) = 1 mol
We know that 1 mol of NO needs to react with 0.5 mol of O2. Let us check if we have that much O2.

8/(16+16) = 0.25 => so we don't have that much O2. So O2 is the limiting reagent, NO is the one in excess and we have 0.5 mol of NO left after the reaction (assuming the reaction goes to completion)

[KenT13]

The mass spectrum of chlorine gas is made up of three peaks at m/e 70, 72 and 74.

The ratio of the relative abundance of these peaks is 9:6:1.

Explain these observation.
(The relative abundance of chlorine-35 and chlorine-37 are approximately 75% and 25% respectively.)

Answer:
The peak at m/e 70 is caused by the ion 35Cl ? 35Cl
The peak at m/e 72 is caused by the ion 35Cl ? 37Cl
The peak at m/e 74 is caused by the ion 37Cl - 37Cl
The ratio of relative abundance Cl-35 : Cl-37
= 75 : 25
= 3 : 1
Hence, The relative heights (abundance) of the peaks
= (3x3) : (2x3x1) : (1x1)
=9 : 6 : 1

Why have to times 2??

Peak at m/e 72 is caused by both 35Cl-37Cl and 37Cl-35Cl. so u must times 2.

[weiliang]

Originally Posted by KenT13

Peak at m/e 72 is caused by both 35Cl-37Cl and 37Cl-35Cl. so u must times 2.

isnt 35Cl-37Cl and 37Cl-35Cl the same???

[yinyin93]

Originally Posted by weiliang

isnt 35Cl-37Cl and 37Cl-35Cl the same???

It can be either 35Cl-37Cl or 37Cl-35Cl means got 2 possible either 35Cl is on left or right hand side?

[weiliang]

Originally Posted by yinyin93

It can be either 35Cl-37Cl or 37Cl-35Cl means got 2 possible either 35Cl is on left or right hand side?

but isn't it the same product?? so now we have to nkow HOW the product come from to know its relative abundance??