Chemical Kinetic - Async

Which of the following is CORRECT?

• E_a1 represents uncatalysed reaction with fewer effective collision.

• E_a1 represents uncatalysed reaction with more effective collision.

• E_a1 represents catalysed reaction with more effective collision.

• E_a1 represents catalysed reaction with less effective collision.

Answer explanation

-catalysts provide alternative pathway with a lower E_a.

-more molecule will posses the minimum energy required. -On the Maxwell distribution curve, the line on the left will represent the catalysed reaction,

-a greater area on the curve, represents more molecules with minimum energy to react.

Consider the reaction: A + B → Products; rate =K[A]³[B]⁰

if concentration of A is doubled and concentration of B is halved, then reaction rate _____.

• will increase by 4x

• will increase by 8x

• is doubled

• will increase by 6x

Answer explanation

rate =K[A]³[B]⁰

change in [B] has no effect on rate since its a zero order

change in [A] = increase by 2

[A]³ = [2]³ = 8 ; Rate increase by 8x

Although it is a third order, and is not under our syllabus, but if u understand the concept from second order, you will be able to do this.

If a reaction’s rate is represented as rate = k [A]² [B], the reaction’s overall order will be ____.

• 2

• 1

• 3

Answer explanation

overall order = 2+1 = 3

A reaction’s rate constant is k=3.28 × 10^-4 s^-1. Determine the reaction’s order.

• zero order

• First order

• second order

• not enough information

Answer explanation

Refer to slide chemical kinetic 2. k for a first order rxn has a unit of s^-1.

Consider the combustion of the following organic compound:

2C₂H₆(g) + 7O₂(g) --> 4CO₂(g) + 6H₂O(l)

Which of the following is CORRECT?

• CO₂ is formed twice as fast as ethane is consumed.

• the rate of consumption of ethane is seven times faster than the rate of consumption of oxygen.

• water is formed at a rate equal to two-thirds the rate of formation of CO₂.

• the rate of consumption of oxygen equals the rate of consumption of water.

Answer explanation

first u need to understand the differential rate equation!

The decomposition of carbon disulfide, CS₂, is first order with k = 2.8 x 10^-7 s^-1 at 1000^oC.

What is the half-life of this reaction at 1000^oC?

• 2.5 x 10⁶ s

• 4.0 x 10^-7 s

• 7.5

• 1.2 x 10⁶

Answer explanation

t1/2=ln2/k

Suppose the reaction: A + 2B --> AB₂ occurs by the following mechanism:

Step 1 : A + B --> AB slow

Step 2: AB + B --> AB₂ fast

What is the rate law equation?

• rate = k[A]²[B]²

• rate = k[A]+[B]

• rate = k[A]-[B]

• rate = k[A][B]

Answer explanation

We can determine the rate law from the RDS (slow step)

What is the rate law equation?

• Rate = k[NH₄⁺][NO₂^-]

• Rate = k[NH₄⁺]²[NO₂^-]²

• Rate = k[NH₄⁺]²[NO₂^-]

• Rate = k[NH₄⁺][NO₂^-]²

Answer explanation

Compare experiment 2&1 if you wish to find the order w.r.t NH₄⁺

Compare experiment 3&1 if you wish to find the order w.r.t NO₂^-

A reaction which follows first-order kinetics is 17.9% complete after 11.4 seconds. What is the rate constant?

• 0.1509

• 0.1068

• 0.0173

• 2.2484

Answer explanation

[A]_o  = 100

[A]_t = 100 – 17 .9 = 82.1 remains   [A]_t = concentration remains

ln (100/82.9) = k (11.4s)

Which of the following represents First order?

• 
• 
• 
• 

Answer explanation

memorise ya!