Rate Constant Calculator

Calculate reaction rates, rate constants (k), or concentrations over time. Supports zero, first, and second order reactions with integrated rate law equations.

Rate constant value with proper units

Concentration of reactant

Initial concentration for time calc

Final concentration after time

Reaction time

Half-life for first order

Rate Laws: Zero Order: Rate = k [A] = [A]₀ - kt First Order: Rate = k[A] [A] = [A]₀e^(-kt) t½ = 0.693/k Second Order: Rate = k[A]² 1/[A] = 1/[A]₀ + kt t½ = 1/(k[A]₀) Where: • k = Rate constant • [A] = Concentration • t = Time • t½ = Half-life
Example 1 (First Order Rate): k = 0.05 s⁻¹, [A] = 0.1 M Rate = 0.05 × 0.1 = 0.005 M/s Half-life = 0.693/0.05 = 13.86 s Example 2 (Find k from concentration): First order, [A]₀ = 0.5 M, [A] = 0.25 M, t = 30 s k = (1/30) × ln(0.5/0.25) = 0.0231 s⁻¹ Example 3 (Second Order): k = 0.1 M⁻¹s⁻¹, [A]₀ = 1 M, t = 10 s 1/[A] = 1 + 0.1 × 10 = 2 [A] = 0.5 M Example 4 (Zero Order): k = 0.01 M/s, [A]₀ = 0.5 M, t = 20 s [A] = 0.5 - 0.01 × 20 = 0.3 M Amount reacted = 0.2 M

What is a rate constant in chemistry?

The rate constant (k) quantifies the speed of a chemical reaction. For a first-order reaction, rate = k[A] with units s⁻¹. For second-order, rate = k[A]² with units M⁻¹s⁻¹. Higher k means faster reaction. The value depends on temperature and is determined experimentally.

How do you calculate reaction rate?

For zero-order: Rate = k (constant regardless of concentration). For first-order: Rate = k[A]. For second-order: Rate = k[A]². The rate depends on the rate constant (k), concentration of reactants ([A]), and reaction order (n). Rate is in M/s (moles per liter per second).

What is the difference between reaction order and rate constant?

Reaction order describes how rate depends on concentration (empirically determined, can be 0, 1, 2, or fractional). Rate constant (k) is the proportionality constant in the rate law that links concentration to rate. Order is unitless; k has units that depend on order to give correct rate units.

How do I calculate concentration over time?

Zero-order: [A] = [A]₀ - kt. First-order: [A] = [A]₀e^(-kt). Second-order: 1/[A] = 1/[A]₀ + kt. These integrated rate laws let you calculate remaining concentration after any time, or find time needed to reach a specific concentration.

What units does the rate constant have?

Zero-order: M/s (mol/L/s). First-order: s⁻¹ (1/s). Second-order: M⁻¹s⁻¹ (L/mol/s). Third-order: M⁻²s⁻¹. The units ensure rate (M/s) results from k × [A]^order. Always check units when working with rate constants!

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