# A level Chemistry help

Watch
Announcements
#1
) Calculating a reactant from Kc:
• This time you are told Kc at the start and initial moles and equilibrium moles.
• Remember to convert to equilibrium concentrations.
6.00 moles of PCl3 is mixed with an unknown amount of Cl2. 2.00 moles of PCl5 is made.
How many moles of Cl2 was added? Kc = 20. The experiment was carried out in a 2dm3
Reaction PCl3(g) + Cl2(g) PCl5(g)
Stoichiometry 1 1 1
Initial n moles 6.00 x 0.0
Reacted
n moles at equilibrium 2.00
[Eq]
• Write the equilibrium expression, put in the values, calculate Kc and work out the units:

I've worked out the equilibrium expression but what would the answer to the question?
0
1 month ago
#2
(Original post by Shafxx)
) Calculating a reactant from Kc:
• This time you are told Kc at the start and initial moles and equilibrium moles.
• Remember to convert to equilibrium concentrations.
6.00 moles of PCl3 is mixed with an unknown amount of Cl2. 2.00 moles of PCl5 is made.
How many moles of Cl2 was added? Kc = 20. The experiment was carried out in a 2dm3
Reaction PCl3(g) + Cl2(g) PCl5(g)
Stoichiometry 1 1 1
Initial n moles 6.00 x 0.0
Reacted
n moles at equilibrium 2.00
[Eq]
• Write the equilibrium expression, put in the values, calculate Kc and work out the units:

I've worked out the equilibrium expression but what would the answer to the question?
Rearrange to get the unknown concentration and fill in the others to solve.
0
1 month ago
#3
(Original post by Shafxx)
) Calculating a reactant from Kc:
• This time you are told Kc at the start and initial moles and equilibrium moles.
• Remember to convert to equilibrium concentrations.
6.00 moles of PCl3 is mixed with an unknown amount of Cl2. 2.00 moles of PCl5 is made.
How many moles of Cl2 was added? Kc = 20. The experiment was carried out in a 2dm3
Reaction PCl3(g) + Cl2(g) PCl5(g)
Stoichiometry 1 1 1
Initial n moles 6.00 x 0.0
Reacted
n moles at equilibrium 2.00
[Eq]
• Write the equilibrium expression, put in the values, calculate Kc and work out the units:

I've worked out the equilibrium expression but what would the answer to the question?
The equilibrium concentration for PCl3 is 4/2 = 2
The equilibrium concentration for PCl5 is 2/2 = 1

Write the expression: Kc = [PCl5] / [PCl3][Cl2]

Rearrange and fill in what you know to find [Cl2]: [Cl2] = 2[Cl2] = 1 / 20

[Cl2] = 0.025

Work out moles of Cl2 by multiplying by the volume of solution: 0.025 x 2 = 0.05

Work out initial Cl2 moles by adding the change in moles to the moles at equilibrium: 2 + 0.05 = 2.25mol

Tell me if any of this didn’t make sense, hope it did though!
0
1 month ago
#4
(Original post by M2003J)
The equilibrium concentration for PCl3 is 4/2 = 2
The equilibrium concentration for PCl5 is 2/2 = 1

Write the expression: Kc = [PCl5] / [PCl3][Cl2]

Rearrange and fill in what you know to find [Cl2]: [Cl2] = 2[Cl2] = 1 / 20

[Cl2] = 0.025

Work out moles of Cl2 by multiplying by the volume of solution: 0.025 x 2 = 0.05

Work out initial Cl2 moles by adding the change in moles to the moles at equilibrium: 2 + 0.05 = 2.25mol

Tell me if any of this didn’t make sense, hope it did though!
Can you help me pls with this question because I’m getting 5 different products
0
1 month ago
#5
(Original post by mh2410)
Can you help me pls with this question because I’m getting 5 different products
The products you get are CH3-CH=CH-CH2-CH3 and CH2=CH-CH2-CH2-CH3. The first product displays cis/trans isomerism so has 2 isomers. Therefore, the answer is 3.
0
1 month ago
#6
(Original post by M2003J)
The products you get are CH3-CH=CH-CH2-CH3 and CH2=CH-CH2-CH2-CH3. The first product displays cis/trans isomerism so has 2 isomers. Therefore, the answer is 3.
What about the structural isomers of CH2=CH-CH2-CH2-CH3
0
1 month ago
#7
(Original post by mh2410)
What about the structural isomers of CH2=CH-CH2-CH2-CH3
Apart from but-1-ene and but-2-ene no other structural isomers are possible because the nucleophile (in this case :OH) has to attack the hydrogen atoms on the carbon adjacent to the carbon bearing the bromine. Therefore it is 3 as you can only get but-1-ene, E-but-2-ene and Z-but-2-ene
1
1 month ago
#8
(Original post by macca_garlick)
Apart from but-1-ene and but-2-ene no other structural isomers are possible because the nucleophile (in this case :OH) has to attack the hydrogen atoms on the carbon adjacent to the carbon bearing the bromine. Therefore it is 3 as you can only get but-1-ene, E-but-2-ene and Z-but-2-ene
Appreciate it , thank you. In a nutshell , during these kind of reaction, not other isomers occur accept the concerned carbons ?
0
1 month ago
#9
(Original post by mh2410)
Appreciate it , thank you. In a nutshell , during these kind of reaction, not other isomers occur accept the concerned carbons ?
Yep exactly. Becuase the nucleophile has to attack the hydrogens hydrogen atoms on the carbon adjacent to the carbon bearing the bromine only 3 isomers can form. The isomer you sent was a structural isomers, but would not have been produced from this reaction mechanism.
0
X

new posts Back
to top
Latest
My Feed

### Oops, nobody has postedin the last few hours.

Why not re-start the conversation?

see more

### See more of what you like onThe Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

### Poll

Join the discussion

#### Do you have the space and resources you need to succeed in home learning?

Yes I have everything I need (420)
56.6%
I don't have everything I need (322)
43.4%