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Rate Constant Calculator

Enter the values to calculate the rate of change and the rate of reaction in dynamic processes.

Elementary step::

rate = K[B]²

Concentration [B]:

Order Of Reaction (Molecule D):

M ▾

Second T_1/2:

sec ▾

Related

Rate Constant Calculator

Use the rate constant calculator to determine the rate constant and reaction rate for a given substance over a specified period. It simplifies the calculation of reaction kinetics.

Rate Constant & Reaction Rate

Rate constant (k) is the proportionality constant relating reactant concentration to reaction rate.

The rate constant indicates how fast or slow a reaction occurs. It depends on temperature and activation energy. Higher temperature increases k, while higher activation energy decreases it.

Reaction rate is the change in concentration of reactants or products per unit time.

Reaction rate is influenced by reactant concentration, temperature, catalysts, and surface area.

Formula

kt = [R₀] – [R]
k = ([R₀] – [R]) / t

k = Rate constant
[R₀] = Initial concentration of reactant
[R] = Concentration at time t

How to Calculate the Rate Constant

Example:

Initial concentration of A ([A₀]) = 0.2 M, after 30 minutes [A] = 0.1 M. Find k for a first-order reaction.

Solution:

For a first-order reaction:

[A] = [A₀] · e^(-kt)

[A] = 0.1 M
[A₀] = 0.2 M
t = 30 min

Step 1: Substitute values: 0.1 = 0.2 · e^(-k·30)

Step 2: Divide both sides by 0.2: e^(-k·30) = 0.5

Step 3: Take natural logarithm: -k·30 = ln(0.5)

Step 4: Solve for k: k = -ln(0.5)/30

This gives the first-order rate constant.

Laws of Rate Constant

Reaction rate can follow Zero, First, or Second-order kinetics.

Zero Order

Rate is independent of reactant concentration. Half-life: t₁/₂ = [A₀] / (2 × k)

Zero Order Rate Constant

First Order

Rate is directly proportional to reactant concentration. Half-life: t₁/₂ = 0.693 / k
Rate = k × [A]

First Order Rate Constant

Second Order

Rate ∝ square of one reactant or product of two reactants. Half-life: t₁/₂ = 1 / (k × [A])

One reactant: Rate = k × [A]²
Two reactants: Rate = k × [A] × [B]

Second Order Rate Constant

FAQs

What is Half-life (t₁/₂)?

Half-life is the time required for a substance to decrease by half. In radioactive decay, it's the time for half of a substance to decay. For drugs, it may take ~5 half-lives to be cleared.

What is the Unit of Rate Constant?

Depends on reaction order. Example: L·mol⁻¹·s⁻¹ for second-order reactions.

Relation Between Temperature & Rate Constant

Higher temperature generally increases the rate constant, while lower temperature decreases it.

Can the Rate Constant (k) Be Negative?

No, k is always positive as it represents the speed of concentration change over time.

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