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Kc working

Ethanoic acid can be manufactured by the following reaction, which is carried out between 150 °C and 200 °C.
CH3OH(g) + CO(g) ---> CH3COOH(g)

a) A mixture 17.6 moles of methanol and 19.6 moles of carbon monoxide is allowed to reach equilibrium at 175°C in a container with volume 5 dm3. It was found that 12.2 moles of ethanoic acid had been formed.

iii) Hence calculate Kc (to 3 significant figures) including its units
(2 marks)

c) Another sample containing 17.6 moles of methanol and 19.6 moles of carbon monoxide was allowed to reach equilibrium, but at a lower temperature. This time it was found that 77.6% of methanol had reacted.
i) Calculate the value of Kc at the lower temperature. Give your answer to 3 significant figures.
(6 marks)

for question a)iii) I got 1.53 for kc

but for question c) i) do we assume the volume is 1dm3 or 5dm3 from above

thanks

Reply 1

EierVonSatan

Your numerical answer for a)iii) is fine, but remember the units :biggrin:

As for c)i) unless they've stated in the question that the volume of the new sample is 1 dm³ then don't assume it :p:

I'd expect it to be the same volume as part a, there is probably a later part in the question that compares the two values for the different temperature.

Reply 2

otrivine

Original post by EierVonSatan

Your numerical answer for a)iii) is fine, but remember the units :biggrin:

As for c)i) unless they've stated in the question that the volume of the new sample is 1 dm³ then don't assume it :p:

I'd expect it to be the same volume as part a, there is probably a later part in the question that compares the two values for the different temperature.

Yes , there is a question which says , is it exothermic or endothermic ! Will it be exothermic

Reply 3

EierVonSatan

Original post by otrivine

Yes , there is a question which says , is it exothermic or endothermic ! Will it be exothermic

If the reaction was exothermic, would you expect to see an increase or a decrease in the value for K_c at a lower temperature?

Reply 4

otrivine

Original post by EierVonSatan

If the reaction was exothermic, would you expect to see an increase or a decrease in the value for K_c at a lower temperature?

You would expect an increase in Kc

Reply 5

EierVonSatan

Original post by otrivine

You would expect an increase in Kc

Reply 6

otrivine

Original post by EierVonSatan

Fantastic

a) MnO4- + U3+ → Mn2+ + UO2+ in aqueous acid (H+ present) conditions
b) Cr2O72- + C2O42- → CO2 + Cr3+ in aqueous acid (H+ present) solutions

(i) Identify which species is the oxidizing agent and which is the reducing agent.

for a) oxidising agent = Mno4 - and reducing agent is U3+

b) oxidising agent = Cr2o7 2- and reducing agent is C2o4 2- ?

Reply 7

EierVonSatan

Original post by otrivine

Fantastic

Yep, pretty straight forward there :smile:

Reply 8

otrivine

Original post by EierVonSatan

Yep, pretty straight forward there :smile:

e) [PF4]+[PF6]-

thanks and the oxidation number for the underlined P, is it +5 ? thanks

Reply 9

otrivine

Original post by EierVonSatan

Your numerical answer for a)iii) is fine, but remember the units :biggrin:

As for c)i) unless they've stated in the question that the volume of the new sample is 1 dm³ then don't assume it :p:

I'd expect it to be the same volume as part a, there is probably a later part in the question that compares the two values for the different temperature.

so the answer would be 2.91? correct

ok if at high temp we get 1.53 and lower temp we get 2.91 for Kc , I keep thinking that because Kc decreases this means forward reaction is exothermic