Comments on: O Level Chemistry: Energy Changes (Exo/Endo) & Bond Energy

By: Dimeji Ajasin

Dimeji Ajasin — Fri, 26 Aug 2011 16:48:16 +0000

Pls I would like to know if an exothermic reaction can be reversed and then the same amount of heat regenerated over and over again? and if it is possible what comination of chemicals would one require for that? Looking forward to hearing from you. Thanks for your anticipated answer.

By: zulfiqar

zulfiqar — Sun, 06 Mar 2011 15:55:55 +0000

i am pakistani u ? any website which tell about questions about electrolysis ,helping to prepare tests plz thanx

By: sadia

sadia — Fri, 16 Apr 2010 04:29:05 +0000

reaction is exothermic bc its a bond making reaction and energy of bond formation 862kj is greater than bond breaking.

By: Saud

Saud — Fri, 19 Feb 2010 17:30:49 +0000

from the given information

H-H bond’s energy=436 kj
Cl-Cl bond’s energy=242 kj

o total energy on reactants side= 436+242

=678 kj

similarly,

H-Cl bond’s energy=431 kj

so total enery on products side =2 x 431

=862 kj

so by the formula del H rteactants-del H products

678-862= -184 and “-” sign indicates an exothermic reaction as total energy of bond forming is greater than total energy of bond breaking………….. am i corect??????????

By: sean

sean — Mon, 15 Dec 2008 03:25:01 +0000

Hi Brinda,

Well done. Your answer is correct and i like the way you present it.

Examiners marking your exam papers will be equally happy to see it too.

PS: Just note that units “kj/mol” need to be reflected at your final answer of “-184 kj/mol”. If not marks will be taken away. It seems like you made the same error like Gary. Rmbr to reflect the units when showing your final answer/working.

Hope this helps.

Cheers
Sean
Master Trainer
Author