Question

When formic acid is heated, it decomposes to hydrogen and carbon dioxide in a first-order decay:

HCOOH(g) →CO2(g) + H2 (g)

The rate of reaction is monitored by measuring the total pressure in the reaction container.

Time (s) . . . P (torr)
0 . . . . . . . . . 220
50 . . . . . . . . 324
100 . . . . . . . 379
150 . . . . . . . 408
200 . . . . . . . 423
250 . . . . . . . 431
300 . . . . . . . 435

At the start of the reaction (time = 0), only formic acid is present. What is the formic acid pressure (in torr) when the total pressure is 291? half-life in sec? What is the rate constant (in s-1)?

Answer 1

pressure of formic acid=149torr,rateconstant=0.012s-1

Answer 2

You can tell by the units that the rate order is 1 (s\(^{-1}\))

Answer 3

but how did you get the answer? can you please write the steps thank you.

Answer 4

did u ask me?

Answer 5

do you know integral form of first order rate equation

Answer 6

[A] = [A]oe-kt ?

Answer 7

yes using that you can find k that is rate constant

Answer 8

take hcooh is A then[A]o=220torr

Answer 9

at50sec let HCOOH is xtorr used up then final HCOOH=220-x
finalCO2=x,finalH2O=x
but given total pressure is 324 torr at 50sec
so220-x+x+x=324
x=104
[A]=220-x= 116
use them

Answer 10

if the total pressure is 291torr then
220-x+x+x=291
x=71
pressure of HCOOH=[A]=220-x=149

Answer 11

in such problems always assume x amount is used up and continue with given data

Answer 12

since one mole ofHCOOH gives one mole each of CO2 andH2O
xamount also gives in same ratio

Answer 13

now is that clear to you shushu55

Answer 14

plz reply

Answer 15

oh i see so since Ao=220 I form an equation and set it equal to the give total pressure, in this case 291. Then I find x by solving the equation which is 71 & then again 220-71=149. Yep I think I got it thank you.

Answer 16

you're smart got it very fast

Answer 17

it took me 1month to find that technique

Answer 18

lol thanks:) you just explained it well. Trust me I'm lost in chemistry.