The rate law for a reaction A + B rightarrow products is rate = k [A]^2. What wi

Question

The rate law for a reaction A + B rightarrow products is rate = k [A]^2. What will be the effect on the reaction rate if the concentration of B is doubled but the concentration of A is unchanged? a. rate is doubled b. rate is halved c. rate is unchanged d. rate is quadrupled e. rate is tripled 7. The xhemical reaction 5Br(aq) + BrO_3^-(aq) + 6H^+(aq) rightarrow 3Br_2(aq) + 3H_2O(l) has the rate law: rate = k[Br^-][BrO_3^-][H^+]^2. What is the overall order of the reaction? a. 5 b. 4 c. 3 d. 2 e. 1 8. The half life of a first order reaction A rightarrow Products is 2.00 min when the initial concentration of A is 1.00 M. What will be the half life of this reaction when the initial concentration of A is 0.500 M? a. 0.347 min b. 1.00 min c. 4.00 min d. 0.250 min e. 2.00 min 9. At 184 degreeC, the equilibrium constant K is 1.48 times 10^4 for the reaction: 2 NO (g) + O_2 (g) 2 NO_2 (g) Calculate the value of K for the following reaction: 4NO_2 (g) 4NO (g) + 2O_2(g) a. 5.92 times 10^4 b. 6.76 times 10^5 c. 4.56 times 10^9 d. 2.19 times 10^8 c. 1.35 times 10^-4 10. For which of the following reactions are the numerical values for K_p and K the same? i. 2SO_2(g) + O_2(g) 2SO_3(g) ii. N_2(g) + O_2(g) 2NO(g) iii. H_2(g) + I_2(g) 2HI(g) a. i only b. ii only c. i and ii d. ii and iii e. i, ii. and iii

Explanation / Answer

6)

Given reaction,

A+ B -------> Product

Rate = k [A]2

Hence its clear that rate of reaction doesn’t depend on [B] hence,

Change concentration of B [B] doesn’t affect rate of the reaction.

Even if [B] is doubled rate is unchanged (option-c).

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7)

Given chemical reaction,

5Br- (aq.) + BrO3- (aq.) + 6H+ (aq.) -------------> 3Br2 (aq.) + 3H2O (l)

Rate = k[Br-]1[BrO3-]1[H+]2

Hence by the definition of order,

Overall rate order = sum of individual orders (i.e. powers to which concentrations are raised)

So,

Overall rate order = 1 + 1 + 2 = 4

Overall rate order is 4 (Option-b).

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8)

Half-life (T½) is the time required for reaction to reduce to its half concentration.

For First order reaction,

T½ = 0.693/k ……………. (Where, k is rate constant.)

Hence we can say that half-life for the First order reaction is independent of the initial concentration of the reactant.

Therefore half-life will be same with both initial concentration 1.00 M and 0.500 M

Half-life is 2.00 min. (option-e).

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9)

Given reaction,

2NO (g) + O2 (g) <-----------> 2 NO2 (g)

At 184 oC, Equilibrium constant say Kf is 1.48 x 104

For the reverse reaction Equilibrium constant say Kr is just reciprocal of Kf

Hence,

Kr = 1/Kf

Kr = 1/(1.48 x 104)

Kr = 6.76 x 10-5

Hence we write,

For, 2 NO2 (g) <--------> 2NO (g) + O2 (g) ………. Kr = 6.76 x 10-5

Kr = [NO]2[O2]/[NO2]2 = 6.76 x 10-5 ………….. (1)

Now for,

4 NO2 (g) <--------> 4NO (g) + 2O2 (g)

Say K = [NO]4[O2]2/[NO2]4

i.e. K = {[NO]2 [O2] / [NO2]2}2

K = {Kr}2

K = (6.76 x 10-5)2

K = 4.56 x 10-9

(Option-c)

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10)

Relation between Kp and Kc is,

Kc = Kp (RT)n …………… (1)

Where,

n = Number of gaseous products (Np) – Number of gaseous reactants (Nr)

If Np = Nr,

Np – Nr = 0

Hence, n = 0

With n = 0 above eq. (1) takes form,

Kc = Kp (RT)0

Kc = Kp x 1

Kc = Kp       ……At n = 0

Of the given reaction,

For H2 (g) + I2 (g) <------> 2HI (g)

Np = 2

Nr = 1+1 = 2

Hence, n = 0

Hence Kp = kc

i.e. Kp = K

for H2 (g) + I2 (g) <------> 2HI (g) ……. (option-iii)

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