Q C. In the thermal decomposition of a substance A, the rate of reaction is foun
ID: 699019 • Letter: Q
Question
Q C. In the thermal decomposition of a substance A, the rate of reaction is found to increase by a factor of 4 when the initial concentration is doubled. What is the order of the reaction with respect to A? Q D. Estimate the temperature at which the rate constant is 0.15 s1 for the decomposition of dinitrogen pentoxide knowing that the rate constant is 2.5 x 103 s1 at a temperature of 332 and that the energy of activation is 1.0 x 105 J/ mol. Q E. The Kp value for the reaction: ½ H2(g) + ½ 12(g) HI(g) is 7.07 at 718 K. What is the Kc value for the reaction: HI(g) ½ H2(g) + ½ 12(g) at the same temperature?Explanation / Answer
1.Rate of reaction (-dCA/dt) of substance A is related to rate constant K and order n as
-dCA/dt = KCAn, (1) –ve sign indicates consumption of A.
When the concentration is doubled, the .i.e. CA= 2CA, the rate has increased by 4 times,
So Eq.1 becomes – 4*dCA/dt= K(2CA)n -(2)
Eq.2/Eq.1 gives 4 = 2n, n =2, the reaction is second order with respect to A.
2.
Arrhenius equation at two different temperatures T1 and T2 can be written as
Ln (K2/K1)= (E/R)*(1/T1-1/T2) (1)
Where K2= rate constant at some temperature, T2 =0.15/sec
K1= rate constant at temperature of 332K whose value is 2.5*10-3/s
E =activation energy = 1*105J/mole
R= gas constant = 8.314 J/mole.K
With these values Eq.1 becomes
Ln(0.15/2.5*10-3)= (1*105/8.314)*(1/332-1/T2)
T2= 374 K
3.
For the reaction 0.5H2(g)+0.5I2(g)<-> HI(g)
Kp = PHI/{(PI2)0.5*(PH2)0.5}=7.07
Where P indicates partial pressure of the gas
For the reaction HI<---->à 0.5H2(g)+ 0.5I2(g)
Kp= (PH2)0.5*(PI2)0.5/ PHI=1/7.07= 0.14143
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