XII Chemistry Chapter 4: Chemical Kinetics

Questions and Answers

What is the unit of the rate constant 'k' for a zero order reaction?

L$^{-1}$ s$^{-1}$

s$^{-1}$

mol L$^{-2}$ s$^{-1}$

mol L$^{-1}$ s$^{-1}$ (correct)

What is the relationship between the concentration of R and time for a zero order reaction?

Sinusoidal wave

Parabolic curve

Exponential decay

Straight line (correct)

How is the half-life of a zero order reaction calculated?

$t_{½} = rac{[R]}{k}$

$t_{½} = rac{0.693}{k}$

$t_{½} = k[R]$

$t_{½} = rac{[R_0]}{2k}$ (correct)

What is the correct formula for the half-life of a first order reaction?

$t_{½} = rac{0.693}{k}$ Signup and view all the answers

Which equation represents the Arrhenius equation?

$k = A e^{-Ea/RT}$ Signup and view all the answers

In the context of a first order gas phase reaction where A decomposes into B and C, what is the formula for calculating the rate constant 'k'?

$k = \frac{2.303}{t} \log\left(\frac{p_i}{p_f}\right)$ Signup and view all the answers

What is the formula for calculating the instantaneous rate of reaction?

Rate = $rac{dx}{dt}$ Signup and view all the answers

How is the average rate of reaction expressed?

Rate = $rac{ riangle x}{ riangle t}$ Signup and view all the answers

What does the overall order of a reaction depend on?

Experimental determination of reactants Signup and view all the answers

In the rate law expression Rate = k [A]$^x$ [B]$^y$, what do the variables x and y represent?

The exponents reflecting the order of the reaction Signup and view all the answers

What is the unit of the rate of reaction?

mol L$^{-1}$ s$^{-1}$ Signup and view all the answers

Which of the following expresses the rate of disappearance of reactant A?

Rate = $-rac{d[A]}{dt}$ Signup and view all the answers

Which of the following is true regarding reaction rates?

They depend on the change in concentration over time. Signup and view all the answers

Study Notes

Important Terms and Definitions in Chemical Kinetics

Instantaneous rate is defined as the change in concentration (dx) over an infinitesimal time interval (dt).
Average rate measures the change in concentration (∆x) over a larger time interval (∆t).
Reaction rate can be quantified using the disappearance of reactants and appearance of products, expressed as:
- Rate of disappearance of A: (-\frac{d[A]}{dt})
- Rate of disappearance of B: (-\frac{d[B]}{dt})
- Rate of appearance of C: (\frac{d[C]}{dt})
- Rate of appearance of D: (\frac{d[D]}{dt})
Overall reaction rate can be represented as:
- (-\frac{d[A]}{dt} = -\frac{d[B]}{dt} = \frac{d[C]}{dt} = \frac{d[D]}{dt})
The unit of reaction rate is mol L(^{-1}) s(^{-1}).

Order of Reaction

Rate law expression for a reaction takes the form:
- Rate = (k [A]^x [B]^y)
The order of the reaction is the sum of the exponents: Order = (x + y).
The order cannot be deduced from a balanced equation; it must be determined experimentally.

Zero Order Reaction

The integrated rate law for a zero-order reaction is given by:
- (\frac{dx}{dt} = k [R]^0)
The unit of rate constant (k) is also mol L(^{-1}) s(^{-1}).
The rate constant (k) can be calculated using:
- (k = \frac{[R_0] - [R]}{t})
A plot of concentration versus time results in a straight line with slope -k, intercepting at [R(_0)].
The half-life for a zero-order reaction is calculated as:
- (t_{1/2} = \frac{[R_0]}{2k})

First Order Reaction

The rate law for a first-order reaction is expressed as:
- (k = \frac{2.303}{t} \log \frac{[R_0]}{[R]})
The half-life for a first-order reaction is calculated using:
- (t_{1/2} = \frac{0.693}{k})

Gas Phase Reactions

For first-order gas phase reactions of the form (A(g) \rightarrow B(g) + C(g)):
- The rate constant (k) can be calculated using:
  - (k = \frac{2.303}{t} \log \frac{p_i}{(2p_i - p_t)})
- Where (p_i) is the initial pressure of (A) and (p_t) is the total pressure of the mixture (p_t = p_A + p_B + p_C).

Arrhenius Equation

The Arrhenius equation relates the rate constant (k) to temperature (T) as:
- (k = A e^{-\frac{E_a}{RT}})
A logarithmic form of the Arrhenius equation expresses the relationship between two rate constants at different temperatures:
- (\log \frac{k_2}{k_1} = \frac{-E_a}{2.303R} \left(\frac{1}{T_1} - \frac{1}{T_2}\right))

Collision Theory

Reaction rate can also be expressed as:
- Rate = (P Z_{AB} e^{RT})
Here, (Z_{AB}) is the collision frequency of reactants (A) and (B) and (P) is the probability or steric factor.

Description

Explore key formulae, important terms, and definitions in Chemical Kinetics with this quiz. Designed for class XII students, this assessment will help reinforce your understanding of instantaneous rates and other critical concepts. Test your knowledge and prepare effectively for your examinations.