Chemistry equilibrium question - HELP!

Ok so ive attached the question, so take a looksie, its nothing too long/complicated chemistry AS stuff!

before I answered the question I deduced the following:

•

Forward reaction was endothermic (enthalpy change was positive) - am i right to assume this btw?

•

Backward reaction was exothermic

My answer:

di) Increase in temperature increases the concentration/yield of ethylbenzene
Equilibrium shifts towards endothermic reaction (towards reactants)

Markscheme answer:
Amount of phenylethene / product increases/higher yield
(increased temperature) moves (position of) equilibrium in the
endothermic direction

WHY? WHY DOES THE AMOUNT OF PHENYLETHENE INCREASE?

My answer:

dii)Carrying reaction out at higher pressure increases phenylethene concetration, equilibrium shifts towards reactants/LHS

Markscheme answer:
Amount of phenylethene / product decreases / lower yield
(increased pressure) moves (position of) equilibrium with fewer molecules / moles / particles

AGAIN WHY WHY WHY?

Please help me :frown:

I will be forever indebted

chemistry equilib.png25.5KB

Reply 1

Sifr

OP

14

p.s please quote me so i know ive got a reply
thanks all :smile:

Reply 2

Nymthae

16

The C6H5CHCH2 is the phenylethene. You rightly said the forward reaction is endothermic so it shifts to favour the products. Phenylethene is one of the products therefore increased yield.

C6H5CH2CH3 is the ethylbenzene.

You've just mixed up the molecules, your theory is right.

Original post by Sifr

p.s please quote me so i know ive got a reply
thanks all :smile:

(edited 12 years ago)

Reply 3

Ste2210

Original post by Sifr

Ok so ive attached the question, so take a looksie, its nothing too long/complicated chemistry AS stuff!

before I answered the question I deduced the following:

•

Forward reaction was endothermic (enthalpy change was positive) - am i right to assume this btw?

•

Backward reaction was exothermic

My answer:

di) Increase in temperature increases the concentration/yield of ethylbenzene
Equilibrium shifts towards endothermic reaction (towards reactants)

Markscheme answer:
Amount of phenylethene / product increases/higher yield
(increased temperature) moves (position of) equilibrium in the
endothermic direction

WHY? WHY DOES THE AMOUNT OF PHENYLETHENE INCREASE?

My answer:

dii)Carrying reaction out at higher pressure increases phenylethene concetration, equilibrium shifts towards reactants/LHS

Markscheme answer:
Amount of phenylethene / product decreases / lower yield
(increased pressure) moves (position of) equilibrium with fewer molecules / moles / particles

AGAIN WHY WHY WHY?

Please help me :frown:

I will be forever indebted

ok so positive enthalpy means an endothermic forward reaction, therefore increasing temp will favour the forward endothermic reaction in order to take in this added heat, for part two, the opposite occurs, more reactant is formed because it has least moles on its side of the equation (product side has 1 mole of each product=2moles) high pressures favour the side with the least moles

Reply 4

Ste2210

i agree with nymthae, uve simply mixed up the names of the molecules

Reply 5

Sifr

OP

14

Original post by Nymthae

The C6H5CHCH2 is the phenylethene. You rightly said the forward reaction is endothermic so it shifts to favour the products. Phenylethene is one of the products therefore increased yield.

C6H5CH2CH3 is the ethylbenzene.

You've just mixed up the molecules, your theory is right.

Oh deary me, I hope I dont make such a diabolical mistake in the actual exam.
Thank you all :smile:

Chemistry equilibrium question - HELP!

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