Reaction Rate Calculator

Calculate reaction rate, rate constant (k), or concentration change. Supports zero, first, and second order reactions. Enter concentration data and time interval to determine kinetic parameters.

Core Formulas: Average Reaction Rate: Rate = -Δ[Reactant]/Δt = Δ[Product]/Δt Rate = |[A]final - [A]initial| / Δt Rate Laws by Order: • Zero Order (n=0): Rate = k k units: M/time • First Order (n=1): Rate = k[A] k units: time⁻¹ k = Rate / [A] • Second Order (n=2): Rate = k[A]² k units: M⁻¹·time⁻¹ k = Rate / [A]² General Rate Law: Rate = k[A]ⁿ where n is the reaction order Arrhenius Equation (temperature dependence): k = A·e^(-Ea/RT) where: • A = pre-exponential factor • Ea = activation energy • R = 8.314 J/(mol·K) • T = temperature (K)
Example 1 (First Order Decomposition): Decomposition of N₂O₅: 2N₂O₅ → 4NO₂ + O₂ [N₂O₅]₀ = 0.100 M [N₂O₅] = 0.0707 M after 50 s Δ[N₂O₅] = 0.0707 - 0.100 = -0.0293 M Rate = 0.0293 M / 50 s = 5.86×10⁻⁴ M/s Average [N₂O₅] = 0.0854 M k = Rate/[N₂O₅] = 5.86×10⁻⁴/0.0854 = 6.86×10⁻³ s⁻¹ Example 2 (Zero Order Reaction): Catalytic decomposition on surface: [A]₀ = 1.50 M [A] = 1.20 M after 100 s Rate = (1.50 - 1.20)/100 = 0.003 M/s k = 0.003 M/s (zero order) Example 3 (Second Order Reaction): 2NO₂ → 2NO + O₂ [NO₂]₀ = 0.0100 M [NO₂] = 0.0050 M after 200 s Rate = 0.0050/200 = 2.5×10⁻⁵ M/s Average [NO₂] = 0.0075 M k = 2.5×10⁻⁵/(0.0075)² = 0.444 M⁻¹s⁻¹ Example 4 (Using Rate Constant): Given: k = 0.0500 s⁻¹ (first order) [A]₀ = 0.200 M, t = 10 s Average [A] ≈ 0.180 M (estimated) Rate = k[A] = 0.0500 × 0.180 = 0.009 M/s Δ[A] = Rate × t = 0.009 × 10 = 0.09 M

What is reaction rate?

Reaction rate is the speed at which reactants are consumed or products are formed in a chemical reaction. It is typically expressed as the change in concentration per unit time (M/s, M/min, etc.). Rate = -Δ[Reactant]/Δt or +Δ[Product]/Δt. The negative sign for reactants indicates their concentration decreases.

What is the rate constant (k)?

The rate constant (k) is a proportionality constant in the rate law equation that relates reaction rate to reactant concentrations. Its value depends on temperature and the specific reaction, but not on concentration. For a reaction aA → products, Rate = k[A]ⁿ, where n is the reaction order. Units of k vary with reaction order.

What is reaction order?

Reaction order (n) indicates how the rate depends on reactant concentration. Zero order (n=0): Rate = k (independent of concentration). First order (n=1): Rate = k[A] (doubling [A] doubles rate). Second order (n=2): Rate = k[A]² (doubling [A] quadruples rate). Overall order is the sum of individual orders for each reactant.

How do you calculate reaction rate from concentration change?

Calculate the change in concentration (Δ[concentration] = final - initial) and divide by the time interval (Δt). Average rate = Δ[concentration]/Δt. For reactants, use the negative change. For example, if [A] drops from 2.0 M to 1.5 M in 10 seconds, rate = -(1.5-2.0)/10 = 0.05 M/s.

What factors affect reaction rate?

Reaction rate is affected by: 1) Concentration (higher concentration usually increases rate), 2) Temperature (typically doubles rate per 10°C increase), 3) Catalysts (lower activation energy), 4) Surface area (for heterogeneous reactions), 5) Pressure (for gases), and 6) Nature of reactants (bond strengths, molecular complexity).

How does temperature affect the rate constant?

Temperature affects k through the Arrhenius equation: k = A·e^(-Ea/RT), where A is the pre-exponential factor, Ea is activation energy, R is the gas constant (8.314 J/mol·K), and T is temperature in Kelvin. Typically, k increases exponentially with temperature. A 10°C increase often doubles or triples the rate.

What are the units of the rate constant?

Rate constant units depend on reaction order: Zero order: M/s or M/min. First order: s⁻¹ or min⁻¹. Second order: M⁻¹s⁻¹ or M⁻¹min⁻¹. Third order: M⁻²s⁻¹. The units ensure that when multiplied by concentration terms, the result has units of M/time.

What is instantaneous vs. average rate?

Average rate is calculated over a finite time interval: Δ[concentration]/Δt. Instantaneous rate is the rate at a specific moment, found by taking the derivative d[concentration]/dt or using a very small time interval. Instantaneous rate changes throughout the reaction, while average rate gives an overall measure over the interval.

How do you use the rate law equation?

The rate law relates rate to concentrations: Rate = k[A]ᵐ[B]ⁿ, where m and n are the orders with respect to A and B. Once you know the rate at given concentrations, solve for k: k = Rate/([A]ᵐ[B]ⁿ). Then use k to predict rates at other concentrations. Note: Rate law must be determined experimentally.

What is the difference between rate and rate constant?

Rate is the speed of reaction at a given moment, measured in M/time, and changes as concentrations change during the reaction. Rate constant (k) is specific to each reaction at a given temperature and does NOT change with concentration. k links rate to concentration through the rate law: Rate = k[reactants]ⁿ.

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