rubyp97
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Can somebody please explain what effect the temperature has on the process, in terms of exothermic and endothermic reactions and how this shifts the rate of equilibrium as i am getting really confused !
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(Original post by rubyp97)
Can somebody please explain what effect the temperature has on the process, in terms of exothermic and endothermic reactions and how this shifts the rate of equilibrium as i am getting really confused !
The equation for the Haber Process is

\text N _2 + 3 \text H _2 \rightleftharpoons 2 \text{NH} _3

IIRC, the forward reaction is exothermic, so the reverse must be endothermic.

Increasing the temperature favours the endothermic reaction (due to Le Chatalier's Principle) which means that the equilibrium shifts to the left.

Decreasing the temperature does the opposite.

In an industrial environment, moderately high temperatures are used because even though they shift the equilibrium to the left, they increase the rate of reaction so that a greater yield is produced in a given time.

Hope this helps
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charco
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(Original post by rubyp97)
Can somebody please explain what effect the temperature has on the process, in terms of exothermic and endothermic reactions and how this shifts the rate of equilibrium as i am getting really confused !
The Haber process is exothermic in the forward direction (-46kJ per mol of ammonia formed)

Increasing temperature moves the position of equilibrium towards the direction of endothermic change, i.e. there is less ammonia.

Therefore low temperature favours formation of ammonia, BUT if its too low the rate of attainment of equilibrium is too slow. So a compromise is reached, not too low and not too high (450ºC)

Increasing pressure pushes the equilibrium towards the side with fewer moles of gas, i.e. the right hand side.
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rubyp97
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Ok thanks that great!- does the equilibrium move to the left when the temp increases because the energy starts to be absorbed when the energy is released?
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(Original post by rubyp97)
Ok thanks that great!- does the equilibrium move to the left when the temp increases because the energy starts to be absorbed when the energy is released?
The equilibrium moves to the left in order to minimize the change to the system (i.e. by taking in more energy, you are trying to reduce the effect of the increase in temperature). Google 'Le Chatalier's Principle'.
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rubyp97
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thanks !
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charco
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(Original post by Arithmeticae)
The equilibrium moves to the left in order to minimize the change to the system (i.e. by taking in more energy, you are trying to reduce the effect of the increase in temperature). Google 'Le Chatalier's Principle'.
Le Chatelier's principle is not the reason, it is an empirical rule.

I am not simply being pedantic here. Some examinations boards will not accept LC as an explanation.

The equilibrium moves to the side of endothermic change as the temperature increases because when there is more energy available the rate of the endothermic direction increases more than that of the exothermic direction.

This can be demonstrated by the Maxwell Boltzmann distribution at two different temperatures, showing the activation energy of the forward and reverse reactions.

The activation energy of endothermic change is always larger than that of exothermic change. Hence an increase in available energy affects the rate of the endothermic direction more than the exothermic direction.
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(Original post by charco)
Le Chatelier's principle is not the reason, it is an empirical rule.

I am not simply being pedantic here. Some examinations boards will not accept LC as an explanation.

The equilibrium moves to the side of endothermic change as the temperature increases because when there is more energy available the rate of the endothermic direction increases more than that of the exothermic direction.

This can be demonstrated by the Maxwell Boltzmann distribution at two different temperatures, showing the activation energy of the forward and reverse reactions.

The activation energy of endothermic change is always larger than that of exothermic change. Hence an increase in available energy affects the rate of the endothermic direction more than the exothermic direction.
That's interesting, I haven't heard the reasoning behind it before but my exam board always allowed it

Do you cover Maxwell-Boltzman at GCSE?
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L'Evil Fish
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(Original post by Arithmeticae)
That's interesting, I haven't heard the reasoning behind it before but my exam board always allowed it

Do you cover Maxwell-Boltzman at GCSE?
Nope, it's AS Energetics even then it isn't explained like above.
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(Original post by L'Evil Fish)
Nope, it's AS Energetics even then it isn't explained like above.
Thanks, I was getting a bit scared for a minute there
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