Question

At 700 K acetaldehyde decomposes in the gas phase to methane and carbon monoxide. The reaction is:
CH3CHO(g)→CH4(g)+CO(g)
A sample of CH3CHO is heated to 700 K and the pressure is measured as 0.27 atm before any reaction takes place. The kinetics of the reaction are then followed by measurements of total pressure and these data are obtained:

t(s)	0	1000	3000	7000
PTotal (atm)	0.27	0.30	0.34	0.39

Find total pressure after 1.47×10⁴ s .

Answer 1

CH3CHO <----------------------------> CH4 + CO

0.27                                                  0          0 ---------------------> initial

0.27- x                                              x           x ----------------------->after some time

at 1000 sec:

0.27 - x + x + x = 0.30

0.27 +x = 0.30

x = 0.03

remaining = Pt = 0.24 atm

at 3000 sec:

0.27 + x = 0.34

x = 0.07

remaining = 0.20 = Pt

decomposition of acetaldehyde second order it is known form calculating rate constant at 1000 sec and 3000sec , 7000 sec .we got same value all times

so

k = 1/t [1/Pt - 1/Po]

k = 1/000 [1/0.24 - 1/0.27]

k = 4.63 x 10^-4 M-1 s-1

now at time 1.47 x 10^4 sec

4.63 x 10^-4 = 1/ 1.47 x 10^4   [1/ Pt - 1/0.27]

Pt = 0.095

Po - x = Pt

0.27 - x = 0.095

x = 0.145

total pressure = Pt = Po + x = 0.27 + 0.145 = 0.45atm

total pressure after given time = 0.45 atm