[Catalist] Equilibrium and temperature

[Phil Brown]

Hi Andrew,

If you picture a potential energy diagram, the activation energy will always be higher for the endothermic reaction than it will be for the exothermic reaction. This one I prepared earlier shows an Ea of 50 kJ/mol for the forward exothermic reaction and 150 kJ/mol for the reverse endothermic reaction:

[cid:image002.jpg at 01D36520.FF2FFC10]

This means that the increase in temperature, while it will increase the rates of both reactions, it will have a greater effect on the rate of the endothermic reaction as it is more reliant on heat (it requires more ‘heat’ than the exothermic reaction).

I always try and teach my students to write ‘+ HEAT’ on the right-hand side of the equation for an exothermic reaction and the left-hand side for an endothermic reaction. This allows them to treat HEAT as a ‘substance’ in the equation. Although obviously this is not correct from a physics point of view, it makes it easier to visualise which reaction will be favoured by the temperature change.

Hope that helps a bit.

Phil




Phil Brown
Science Teacher
St George’s Anglican Grammar School
St George’s Anglican Grammar School
A school of the Anglican Schools Commission (Inc.)
50 William St, PERTH WA 6000
p: Locked Bag 15, Cloisters Square, PERTH WA 6850
t:+61 8 9312 0800 | f:+61 8 9312 0899
pbrown at stgeorges.wa.edu.au
www.stgeorges.wa.edu.au
Click here for more information
Disclaimer: The information transmitted is intended only for the person or entity to which it is addressed and may contain confidential and/or privileged material. If you are not the intended recipient of this message you are hereby notified that any use, review, re-transmission, dissemination, distribution, reproduction or any action taken in reliance upon this message is prohibited. If you have received this email in error, please notify us immediately by return email or telephone (08) 9312 0800 and destroy the original message. Any views expressed in this message are those of the individual sender and may not necessarily reflect the views of the organisation.
From: Catalist [mailto:catalist-bounces at lists.stawa.net] On Behalf Of Andrew Bland
Sent: Friday, 24 November 2017 12:11 PM
To: Catalist at lists.stawa.net
Subject: [Catalist] Equilibrium and temperature

Dear chemistry teachers,

When a system is heated, both the forward and reverse reaction rates increase, “but the endothermic reaction increases more than the exothermic reaction. The endothermic reaction is always affected more by a temperature change than the exothermic reaction. This is true even when a system is cooled…” Chem for WA 2.

My question is why is the endothermic reaction rate always effected more than the exothermic rate? I cannot find an explanation in any of my texts, only a re-stating of this in various forms.

Thanks

Andrew



Andrew Bland

Head of Year 10 and Head of Geographe House


T:  +61 8 9752 5252

F:  +61 8 9752 5299

A:  PO Box 920, Busselton WA 6280

E:  abl at gmas.wa.edu.au<mailto:abl at gmas.wa.edu.au>

W: www.gmas.wa.edu.au<http://www.gmas.wa.edu.au>

[cid:image001.jpg at 01D36520.B1017D20]

Disclaimer

This email and any files transmitted with it are confidential and intended solely for the use of the individual or entity to whom they are addressed. If you have received this email in error please inform the sender and delete the email. Do not disseminate, distribute or copy this e-mail without the prior consent of the author. The School has taken reasonable precautions to ensure no viruses are present in this email, and cannot accept responsibility for any loss or damage arising from the email.


-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.stawa.net/pipermail/catalist_lists.stawa.net/attachments/20171124/28281fc9/attachment.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: image001.jpg
Type: image/jpeg
Size: 23081 bytes
Desc: image001.jpg
URL: <http://lists.stawa.net/pipermail/catalist_lists.stawa.net/attachments/20171124/28281fc9/attachment.jpg>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: image002.jpg
Type: image/jpeg
Size: 7012 bytes
Desc: image002.jpg
URL: <http://lists.stawa.net/pipermail/catalist_lists.stawa.net/attachments/20171124/28281fc9/attachment-0001.jpg>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: image957000.png
Type: image/png
Size: 138947 bytes
Desc: image957000.png
URL: <http://lists.stawa.net/pipermail/catalist_lists.stawa.net/attachments/20171124/28281fc9/attachment.png>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: image911001.png
Type: image/png
Size: 3912 bytes
Desc: image911001.png
URL: <http://lists.stawa.net/pipermail/catalist_lists.stawa.net/attachments/20171124/28281fc9/attachment-0001.png>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: image860002.png
Type: image/png
Size: 111063 bytes
Desc: image860002.png
URL: <http://lists.stawa.net/pipermail/catalist_lists.stawa.net/attachments/20171124/28281fc9/attachment-0002.png>