AQA Jun 2013 Paper 2 Q3 (with explained solutions) |

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AQA Jun 2013 Paper 2 Q3

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do not write outside the box the diagram shows the maxwell boltzmann distribution for a sample of gas at a fixed temperature ea is the activation energy for the decomposition of this gas number of molecules energy ea emp is the most probable value for the energy of the molecules a on the appropriate axis of this diagram mark the value of emp for this distribution on this diagram sketch a new distribution for the same sample of gas at a lower temperature marks b with reference to the maxwell boltzmann distribution explain why a decrease in temperature decreases the rate of decomposition of this gas marks turn over wmp jun chem

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mark scheme general certificate of education a level chemistry unit chemistry in action june marking guidance m on the energy axis emp at the maximum of the original peak m the peak of their new curve is displaced to the left and higher than the original m all of the following are required the new curve starts at the origin and should begin to separate from the original almost immediately and the new curve crosses the original curve once and an attempt has been made to draw the new curve correctly towards the energy axis below the original curve but not to touch the original curve or the axis the rate of reaction decreases as the temperature decreases because m a decrease in the number proportion of molecules with e ea or fewer molecules have e ea or fewer molecules have sufficient enough energy to react decompose m fewer effective productive successful collisions in a given time given period or fewer frequent effective productive successful collisions or lower rate of effective productive successful collisions mark comments m the limits for the horizontal position of emp are defined as above the word the in the sentence below the graph in m ignore molecules have less energy ignore less energetic collisions ignore molecules do not gain activation energy ignore fewer collisions credit particles for molecules but not atoms ignore chance of collision this alone does not gain m question a b

Question 1 2 3 4 5 6 7 8 9 10 11

Topics to revise

AQA > Physical chemistry > Energetics and kinetics AS >

5 Kinetics

AQA > Inorganic chemistry > Periodicity AS >

1 Periodicity

AQA > Physical chemistry > Atomic structure AS >

4 Electronic arrangement

AQA > Physical chemistry > Thermodynamics >

2 Born-Haber cycle

AQA > Physical chemistry > Thermodynamics >

5 Gibb’s Free Energy

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