When formic acid is heated, it decomposes to hydrogen and carbon dioxide in a fi

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 50 100 150 200 250 300 220 324 379 408 423 431 435 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 238? Hint: use Dalton's law of partial pressure which states total pressure when you have a mixture of gases a A and B, is given by the expression, P PA+ PB, and the reaction stoichiometry Answer:

Explanation / Answer

1)
HCOOH ---> CO2 + H2

ptotal = pHCOOH+pCO2+pH2

238 = (220-x)+x+x

x = 18 torr

pHCOOH = 220-18 = 202 torr

2)

initial pHCOOH (at t=0sec) = 220 torr

ptotal = pHCOOH+pCO2+pH2

324 = (220-x)+x+x

X = 104,

after t = 50 sec , pHCOOH = 220-104 = 116 torr

first order kinetics

K1 = (1/t)ln(a0/a)

     = (1/50)ln(220/116)

     = 0.0128 s-1

k1 = 0.693/t1/2

t1/2 = half life = 0.693/0.0128 = 54.14 sec

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