jonesy123
Badges: 4
Rep:
?
#1
Report Thread starter 7 years ago
#1
does anyone know how to calculate activation energy for a reation? ive looked at all the equations and cant seem to make sense out of them...
0
reply
nabeel1231
Badges: 5
Rep:
?
#2
Report 7 years ago
#2
activayion energy, as in to work out the minimum temperature for a reaction to occur, can be worked out by deltaG=deltaH - TdeltaS
rearrange the equation to make T the subject

Posted from TSR Mobile
0
reply
nabeel1231
Badges: 5
Rep:
?
#3
Report 7 years ago
#3
come to thing of it im pretty sure if you made deltaH the subject, it'd give you the activation energy in kj/mol

Posted from TSR Mobile
0
reply
charco
Badges: 17
Rep:
?
#4
Report 7 years ago
#4
(Original post by jonesy123)
does anyone know how to calculate activation energy for a reation? ive looked at all the equations and cant seem to make sense out of them...
You cannot work it out without some kinetics information, i.e. the rate constant at different temperatures.

Then use Arrhenius ...

k = Ae-Ea/RT
1
reply
Borek
  • Study Helper
Badges: 4
Rep:
?
#5
Report 7 years ago
#5
ΔH is not the activation energy, it is enthalpy change in the reaction. Completely different concept.
0
reply
jonesy123
Badges: 4
Rep:
?
#6
Report Thread starter 7 years ago
#6
okay yes i can rearange that but i cant calculate the rate constant either...god this is annoying -_-
0
reply
jonesy123
Badges: 4
Rep:
?
#7
Report Thread starter 7 years ago
#7
can i rearrange the rate equation to get the rate constant?
0
reply
charco
Badges: 17
Rep:
?
#8
Report 7 years ago
#8
(Original post by jonesy123)
can i rearrange the rate equation to get the rate constant?
Of course ...

... but only after experimentation to obtain the rates at different concentrations and hence the orders of reaction with respect to the reacting components.

Then repeat the process all over again at a different temperature to get a second datum.

(A shortcut would be to assume that the orders don't change at different temperatures)
0
reply
jonesy123
Badges: 4
Rep:
?
#9
Report Thread starter 7 years ago
#9
yes ive done experiment and found orders of reaction and rates...so i can just plug in numbers and put rate/[concentration]^x and etc? what would the second data set at a different temperature show?
0
reply
charco
Badges: 17
Rep:
?
#10
Report 7 years ago
#10
(Original post by jonesy123)
yes ive done experiment and found orders of reaction and rates...so i can just plug in numbers and put rate/[concentration]^x and etc? what would the second data set at a different temperature show?
You need different values of the rate constant at different temperatures to determine Ea.
0
reply
Peteyology
Badges: 2
Rep:
?
#11
Report 7 years ago
#11
k = Ae-Ea/RT

Note: you will need experimental data to plot an Arrhenius plot, this will give you the value of activation energy of the given reaction:

K
=rate constant
A=exponential factor
ex=quantity(button on calculator)
-Ea=-(activation energy)
R=gas constant (8.31 J K-1 mol-1)
T=temperature (kelvin)

Image
→ we can use this form of the equation to plot lnK against 1/T.
→ This will produce the gradient of -Ea/R:
Image

→ once we have this gradient, we can work out the Ea.
negative change in y (Δy) over change in x (Δx)
→ (-Δy)/Δx=-Ea, therefore, Ea=(-Ea)x (R (8.31))

You could be asked to do this in an exam, i've seen a few papers where you are asked to do an Arrhenius plot from experimental data, good luck!
0
reply
cuckoo99
Badges: 12
Rep:
?
#12
Report 7 years ago
#12
(Original post by Peteyology)
k = Ae-Ea/RT

Note: you will need experimental data to plot an Arrhenius plot, this will give you the value of activation energy of the given reaction:

K
=rate constant
A=exponential factor
ex=quantity(button on calculator)
-Ea=-(activation energy)
R=gas constant (8.31 J K-1 mol-1)
T=temperature (kelvin)

Image
→ we can use this form of the equation to plot lnK against 1/T.
→ This will produce the gradient of -Ea/R:
Image

→ once we have this gradient, we can work out the Ea.
negative change in y (Δy) over change in x (Δx)
→ (-Δy)/Δx=-Ea, therefore, Ea=(-Ea)x (R (8.31))

You could be asked to do this in an exam, i've seen a few papers where you are asked to do an Arrhenius plot from experimental data, good luck!
What exam board is this? the Maths looks so nice
0
reply
Peteyology
Badges: 2
Rep:
?
#13
Report 7 years ago
#13
(Original post by cuckoo99)
What exam board is this? the Maths looks so nice
That is edexcel
0
reply
X

Quick Reply

Attached files
Write a reply...
Reply
new posts
Back
to top
Latest
My Feed

See more of what you like on
The Student Room

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

Personalise

Which of these would you use to help with making uni decisions?

Webinars (54)
13.85%
Virtual campus tours/open days (89)
22.82%
Live streaming events (37)
9.49%
Online AMAs/guest lectures (38)
9.74%
A uni comparison tool (88)
22.56%
An in-person event when available (84)
21.54%

Watched Threads

View All