Endothermic reactions questions.

'Under what temperature conditions do most endothermic reactions occur?'

'Plants photosynthesise well both in the tropics and under arctic conditions, why is this?'

Is the second one something to do with the activation energy coming from sunlight?

Reply 1

oxymoron

7

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'Under what temperature conditions do most endothermic reactions occur?'

'Plants photosynthesise well both in the tropics and under arctic conditions, why is this?'

Is the second one something to do with the activation energy coming from sunlight?

Endothermic reactions must have a favourable entropy because their enthalpy change is unfavourable. This means that they will occur best at high temperatures due to the increased importance of entropy at high temperatures.
Do you know about gibbs free energy and/or entropy? it is in syllabus for some boards and not others.

Yes the second one is because heat is not used to provide the activation energy for photosynthesis so it can occur under any conditions provided there is enough light around to excite the electron from chlorophyll which provides the energy to set the reaction going.

Reply 2

Revenged

15

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'Under what temperature conditions do most endothermic reactions occur?'

'Plants photosynthesise well both in the tropics and under arctic conditions, why is this?'

Is the second one something to do with the activation energy coming from sunlight?

endothermic reactions are favoured by high temperatures.

this is shown by your example, photosynthesis

at low temperatures, the rate of photosynthesis is low because temperature is a limiting factor for photosynthesis

this is because the enzyme RuBiSCO in the light independent reaction catalyses the reaction of RuBP with CO₂ to from GP.

at higher temperatures, the kinetic energy of molecules increases therefore increasing the chance of enzyme-substrate complexes forming, which causes the rate of reaction to increase

i dont know about the second question... it's not very clear

Reply 3

Aired

OP

1

Ok, thanks for that. There's another question I'm not sure on:

Benzene can be manufactured by passing the gaseous hydrocarbon ethyne over finely divided nickel;

3C2H2 (g) ----Nickel----> C6H6 (l)

'Suggest with explanations how the rate of this reaction might be affected by an increase in temperature and an increase in pressure'

Would I use ideas about collisions between benzene and nickel particles for this? Temperature gives more kinetic energy, so there are more succesful collisions. Pressure increases the number of benzene particles within a set volume, so the number of collisions, and therefore succesful collisions is increased?

Reply 4

Revenged

15

is the reaction exothermic or endothemic?

Reply 5

Aired

OP

1

The question doesn't say, I don't see why you'd need to know for a rate of reaction question...

Reply 6

Magician

15

Revenged

is the reaction exothermic or endothemic?

has to be exothermic if order for the final product to be thermodynamically favorable (i think)

Reply 7

Revenged

15

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The question doesn't say, I don't see why you'd need to know for a rate of reaction question...

ok... perhaps not... if this is just a rate of reaction question what you said sounds fine

Reply 8

Magician

15

Aired

'Suggest with explanations how the rate of this reaction might be affected by an increase in temperature and an increase in pressure'

Pressure increases the number of benzene particles within a set volume, so the number of collisions, and therefore succesful collisions is increased?