Dec 14, 2009
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A change in temperature from 10 C to 20 C is found to double the rate off a particular chemical reaction. How did the change in temperature affect the reacting molecules?
a) The average velocity of the molecules doubled
b) average energy of the molecules doubled
c) the number of collisions per second doubled
d) the number of molecules above the reaction energy threshold doubled

Please explain me in detail to support your answer. Thank you
 
Jun 14, 2009
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My guess is D. Because I said so. And because reaction rate is dictated by the rate of collisions between reactants which overcome activation energy.
 

MrBeans

MrBeans
Nov 6, 2009
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I would guess B. Adding heat energy directly effects kinetic energy, thus having an effect on collisions, and ability to reach reaction thresholds.

K.E. = (3kT)/2

Answer A is definitely wrong.
 

UndergradGuy7

10+ Year Member
Jun 23, 2007
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I would guess D. Reactions occur when two molecules collide, but not all result in a reaction. Only those with enough energy and the right orientation will have a reaction. Not all that collide will be orientated the right way and have the activation energy to react.

See here for more information under the temperature part http://www.cdli.ca/sampleResources/chem3202/unit01_org01_ilo03/b_activity.html

so for A, B, C yes the energy doubled etc., but this doesn't mean that the number of molecules that have sufficient energy doubled. For example if the energy required to have a reaction is 5 and all of your reactants have an initial energy of 1 if you doubled it to 2, they still wouldn't react.
 

MrBeans

MrBeans
Nov 6, 2009
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I wish we could find out the true answer... I'm curious now!

D makes perfect sense, actually...

B,C,D all seem to be logical answers to me :oops:
 
Jun 14, 2009
800
3
0
Status
Pre-Dental
I would guess D. Reactions occur when two molecules collide, but not all result in a reaction. Only those with enough energy and the right orientation will have a reaction. Not all that collide will be orientated the right way and have the activation energy to react.

See here for more information under the temperature part http://www.cdli.ca/sampleResources/chem3202/unit01_org01_ilo03/b_activity.html

so for A, B, C yes the energy doubled etc., but this doesn't mean that the number of molecules that have sufficient energy doubled. For example if the energy required to have a reaction is 5 and all of your reactants have an initial energy of 1 if you doubled it to 2, they still wouldn't react.
BTW energy does not double. The temperature was increased from 283K to 293K. That amounts to a 3.5% increase in temp. I wouldn't say that's enough to double any of the variables in options A, B, or C.