[dhoom3]

Here are 2 of the many problems im having hard time with.

1)
t (k)         K (s-1)
338          4.87x10^-3
328          1.50x10^-3
318          4.98x10^-4
308          1.35x10^-4
298          3.46x10^-5
273          7.87x10^-7

a ) Determine the Activation energy (Ea)
      What i got -> y = -12527x + 31.758
                                                          so, -(Ea/R) = -12527
                                                                Ea = (8.314 j/k * mol) (12527 K)
                                                                Ea = 1.04x10⁵ j/mol
                                                                Ea = 1.04x10² kj/mol     (correct?)
b ) Calculate the new rate constant when the temperature is 358 K.
Spot where help needed.

2) 4PH₃(g)  P₄(g) + 6H₂(g)
Rate = k[PH3]
Halflife of PH3 is 37.9 s at 120 C.
   a) How much time is required for three-fourths of the PH₃ to decompose?
   b) What fraction of the original sample of PH₃ remains after 1 min?
Help Needed.

-

[typhoon2028]

FYI:

PH3 = phosphine not phosgene.

Also, phosgene does not contain phosphorus.


Phosgene = CCl2O

[dhoom3]

b ) Calculate the new rate constant when the temperature is 358 K.
Spot where help needed.

i used the formula: ln k = -(Ea/R) (1/T) + ln A ,
since y = -12527 + 31.758
ln K = -12527 * (1/358) + 31.758  (is this setup correct?)
ln K = -3.23
antilog K = 3.96x10^-2 (correct?)

BUT WHEN USED THIS FORMULA: ln (k1/k2) = (Ea/R)((T1-T2)/(T1T2))
                                             

ln (4.87x10^-3s-1/K2) = (1.041x10⁵/8.314)((338-358)/(338)(358))

ln (4.87x10^-3s-1/K2) = -2.07

ln (4.87x10^-3s-1/K2) = e^-2.07 = 0.126

k2 = 3.87x10^-2 (correct?)


still need help with the 2nd problem...

[dhoom3]

give me atleast a hint on what equation to use or example to do the 2nd problem...

2) 4PH3(g)    P4(g) + 6H2(g)
Rate = k[PH3]
Halflife of PH3 is 37.9 s at 120 C.
   a) How much time is required for three-fourths of the PH3 to decompose?
   b) What fraction of the original sample of PH3 remains after 1 min?

[aldoxime_amine]

t (k)         K (s-1)

That is a first order reaction. Are you aware of this relation?
http://en.wikipedia.org/wiki/Integrated_rate_law#Summary_for_reaction_orders_0.2C_1.2C_2_and_n

It is a direct application.