Chemistry · Reaction rate · Equilibrium / Principles and exploration
Concentration, temperature, and reaction rate — principles and investigation
When investigating the cause of a faster reaction, concentration changes and temperature changes must be compared separately. Control the initial concentration and temperature of reactant A and observe the concentration and initial reaction rate over time. Distinguish between the roles of rate constant and concentration in the first-order reaction model of this experiment.
How does it work?
Temperature changes the rate constant k, and concentration changes the initial speed v₀=k[A]₀ at the same k.
k = A·exp(−Ea/RT) · [A] = [A]₀e⁻ᵏᵗ
Try this investigation
- Observe virtual A → B at double speed for 120 s. Orange A changes to green B. Particle collisions are for illustration purposes only and the values are determined by the velocity equation.
- Run and record initial concentrations of 1 and 2 mol/L respectively at 25 °C.
- Set the initial concentration to 1 mol/L, change the temperature to 35 °C, and overlap the curves.
Interpreting your results
What changes if you double the initial concentration in a first-order reaction?
v₀=k[A]₀. At the same temperature, k is constant and the half-life is ln2/k, which is independent of concentration.
Assumptions and limitations
It is a hypothetical first-order irreversible reaction. Use the frequency factor A=1.00×10⁷ s⁻¹, Ea=50 kJ/mol, R=8.314 J/(mol·K). It is a constant volume and temperature, and reverse reaction, diffusion, and heat generation are omitted. The number of particles and number of collisions are not used in calculations.