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activation energy----role of T and catalyst

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  • hoay's Avatar
    166 posts since Jul '11
    • Activation energy is not affected by increasing temperature.It is the catalyst which decreases the Ea but when we say increasing temperature increases the proportion of molecule having energy greater or equal to the activation energyit seems that Ea is linked to temprature. Please explain. 

  • Moderator
    H2 Chemistry @ BedokFunland JC (near VJC & TJC)
    UltimaOnline's Avatar
    14,124 posts since May '05
    • Originally posted by hoay:

      Activation energy is not affected by increasing temperature.It is the catalyst which decreases the Ea but when we say increasing temperature increases the proportion of molecule having energy greater or equal to the activation energyit seems that Ea is linked to temprature. Please explain. 


      Say you have 10 employees, but as a stingy CEO, you underpay them with unethically low wages. One night after work, the 10 of them try to enter a high-class nightclub, but only 2 of them have enough money to afford the $100 entrance fees and enter, while the remaining poorer 8 of them can only wait pitifully outside the club.

      Some years later, after having a near-death experience, your perspectives as a CEO have changed, and now you decide to pay all your 10 employees generously. Now all of them have enough money to pay the $100 entrance fees to enter the nightclub. Happy ending.

  • hoay's Avatar
    166 posts since Jul '11
    • It means that if we increase the temperature the the demand or the parameter for Ea is increased also ....but i am unable to deduce catalyst here...the CEO or salary?

       

  • Moderator
    H2 Chemistry @ BedokFunland JC (near VJC & TJC)
    UltimaOnline's Avatar
    14,124 posts since May '05
    • Originally posted by hoay:

      It means that if we increase the temperature the the demand or the parameter for Ea is increased also ....but i am unable to deduce catalyst here...the CEO or salary?

       


      Catalyst isn't a factor in this story. This story is about increasing their pay so they've enough money to enter, ie. more employees now have enough money (energy) to afford the entrance fee (activation energy).

      For a catalyst story, it would be a near-death experience for the nightclub boss, causing him to decide to lower the entrance fee (activation energy) required to enter (for reaction to occur).

      So EITHER increasing the emplyees' pay (molecules' energy), OR reducing the entrance fee (activation energy) required, would help to increase the % of employees who can enter, hence speed up the rate of the reaction.

      You can of course, do both. But for A levels, Cambridge will test your students on each factor separately, not simultaneously.

  • Metanoia's Avatar
    18 posts since May '15
    • Might be late to the topic, would just like to contribute another analogy that I find students relate to quite well

      Senario is the aftermath of a very difficult test where a large portion of the class has failed, if the teacher wishes to increase the portion of passes

      Marks of students = energy of molecules

      Passing mark = Ea

      1. Lower the passing mark (lower the Ea, by using a catalyst) 

      2. Boost the sudents score (increase energy by boosting the temperature)

       

      Edited by Metanoia 09 Apr `17, 4:19PM
  • Moderator
    H2 Chemistry @ BedokFunland JC (near VJC & TJC)
    UltimaOnline's Avatar
    14,124 posts since May '05
    • Originally posted by Metanoia:

      Might be late to the topic, would just like to contribute another analogy that I find students relate to quite well

      Senario is the aftermath of a very difficult test where a large portion of the class has failed, if the teacher wishes to increase the portion of passes

      Marks of students = energy of molecules

      Passing mark = Ea

      1. Lower the passing mark (lower the Ea, by using a catalyst) 

      2. Boost the sudents score (increase energy by boosting the temperature)

       


      Edited : Ah ok, you actually already informed me when I asked 2 years ago, on 2 separate occasions several months apart in fact. I assume you've moved on to tutoring JC students as well now.

      Edited by UltimaOnline 10 Apr `17, 3:35AM
  • hoay's Avatar
    166 posts since Jul '11
    • A chemist puts a sample of dilute aqueous hydrochloric acid into beaker 1. She adds a sample of zinc and measures the rate of production of hydrogen gas. 
She then puts a different sample of dilute aqueous hydrochloric acid into beaker 2. She adds a different sample of zinc and measures the rate of production of hydrogen gas. 
The rate of the reaction in beaker 2 is greater than the rate of the reaction in beaker 1. Which factors could help to explain this observation?

      1  The reaction in beaker 1 has a higher activation energy than the reaction in beaker 2.

      2  The zinc in beaker 1 is in larger pieces than the zinc in beaker 2.

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      3  The acid in beaker 1 is at a lower concentration than the acid in beaker 2.

      Why statement 3 is wrong as the slow rate may be due to the high activation energy in beaker 1?

  • Moderator
    H2 Chemistry @ BedokFunland JC (near VJC & TJC)
    UltimaOnline's Avatar
    14,124 posts since May '05
    • A chemist puts a sample of dilute aqueous hydrochloric acid into beaker 1. She adds a sample of zinc and measures the rate of production of hydrogen gas. 
She then puts a different sample of dilute aqueous hydrochloric acid into beaker 2. She adds a different sample of zinc and measures the rate of production of hydrogen gas. 
The rate of the reaction in beaker 2 is greater than the rate of the reaction in beaker 1. Which factors could help to explain this observation?

      1 The reaction in beaker 1 has a higher activation energy than the reaction in beaker 2.

      2 The zinc in beaker 1 is in larger pieces than the zinc in beaker 2.

      3 The acid in beaker 1 is at a lower concentration than the acid in beaker 2.

      2 and 3 are correct. 1 is wrong because the same reaction must have the same activation energy.

  • Metanoia's Avatar
    18 posts since May '15
    • Originally posted by UltimaOnline:


      Edited : Ah ok, you actually already informed me when I asked 2 years ago, on 2 separate occasions several months apart in fact. I assume you've moved on to tutoring JC students as well now.

      Yup, we've conversed quite some time ago. 

      As of now, I still sticking with tutoring O level students, but trying to keep myself current with the A-level questions. :)

  • Moderator
    H2 Chemistry @ BedokFunland JC (near VJC & TJC)
    UltimaOnline's Avatar
    14,124 posts since May '05
    • Originally posted by Metanoia:

      Yup, we've conversed quite some time ago. 

      As of now, I still sticking with tutoring O level students, but trying to keep myself current with the A-level questions. :)


      Good for you :)

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