Chemistry A2, rate of reaction Question

[helai.j]

i posted this earlier on the edexcel chemistry doubts but not one is replying ): i hope someone replies here

Q: in a gas phase, molecule A decomposes to molecule B and C at high temperature. A chemist suspects that this reaction is first order with respect to A. in an experiment to explore the kinetics of the reaction, the data in the table were obtained for the decomposition at 800K.

then there is a table with time and partial pressure values for A .
example

T            A/KPA
0               1300
20             1051

and so on, then it says by using a graph find out if this reaction is really first order with respect to A.
for the graph i need concentration/time .  but they have given me pressure. so how will i make the graph ? or turn the pressure into conc.


Q2) the equation for the reaction of bromine and methanoic acid is:
Br2 (aq) + HCOOH ( aq)  ----> 2Br- (aq) + 2H+ (aq) + CO2 (g)

a) suggest a way of keeping the concentration of methanoic acid virtually constant?

[vanibharutham]

for Q1:

the partial pressure of any gas is the product of the mole fraction and the total pressure.... Initially, when t = 0, the only gas present will be A and thus the mole fraction = 1 and the pressure exerted by the gas molecules of A = 1300 kPa. As the reaction progresses, A decomposes to form B and C, and thus the mole fraction decreases from 1 to lets say 0.8 and so on.... and thus the partial pressure decreases as the concentration of A decreases.

Because the above is true, the concentration of A is proportional to the partial pressure of A and thus you can plot a graph of partial pressure against time and it will be an indirect method of plotting concentration against time.


For Q2:

Use HCOOH in excess and then its concentration will remain constant.

[helai.j]

thank you very much ! i appreciate it

[Deadly_king]

for Q1:

the partial pressure of any gas is the product of the mole fraction and the total pressure.... Initially, when t = 0, the only gas present will be A and thus the mole fraction = 1 and the pressure exerted by the gas molecules of A = 1300 kPa. As the reaction progresses, A decomposes to form B and C, and thus the mole fraction decreases from 1 to lets say 0.8 and so on.... and thus the partial pressure decreases as the concentration of A decreases.

Because the above is true, the concentration of A is proportional to the partial pressure of A and thus you can plot a graph of partial pressure against time and it will be an indirect method of plotting concentration against time.


For Q2:

Use HCOOH in excess and then its concentration will remain constant.

Nice job dude......+rep
For question 2.........I would rather use a buffer solution consisting of the acid and its ionic salt NaCOOH.