In a pseudo first order reaction in water, the following results were obtained: t/s: 0, 30, 60, 90 [A]/mol L: 0.55, 0.31, 0.17, 0.085 Calculate the average rate of reaction between the time interval 30 to 60 seconds.
The average rate of reaction between 30 to 60 seconds is ⁻³ mol L⁻¹ s⁻¹.
Step 1: Identify the given data At time t = 30 s, [A] = 0.31 mol L⁻¹ At time t = 60 s, [A] = 0.17 mol L⁻¹
Step 2: Calculate the change in concentration Δ[A] = [A]₂ - [A]₁ = 0.17 - 0.31 = -0.14 mol L⁻¹
Step 3: Calculate the time interval Δt = 60 - 30 = 30 s
Step 4: Calculate the average rate Average rate = -Δ[A]/Δt = -(-0.14)/30 = 0.14/30 = ⁻³ mol L⁻¹ s⁻¹
Explanation
This is a straightforward calculation of average rate of reaction. The average rate is defined as the change in concentration divided by the time interval. Since the concentration of reactant A decreases with time, we use the negative sign convention to express the rate as a positive quantity. The formula used is: Average rate = -Δ[A]/Δt, where Δ[A] represents the change in concentration of reactant A over the time interval Δt.
Solution Steps
Step 1: Identify concentrations at t=30s (0.31 mol L⁻¹) and t=60s (0.17 mol L⁻¹)
Step 2: Calculate Δ[A] = 0.17 - 0.31 = -0.14 mol L⁻¹
Step 3: Calculate time interval Δt = 60 - 30 = 30 s
Step 4: Apply formula: Average rate = -Δ[A]/Δt = -(-0.14)/30 = ⁻³ mol L⁻¹ s⁻¹