1.5 Kinetics Flashcards
What is the activation energy (Ea)?
The minimum energy which particles need to collide to start a reaction.
What does the Maxwell-Boltzmann distribution show?
The spread of energies that molecules of a gas or liquid have at a particular temperature.
Why does the Maxwell-Boltzmann curve start at the origin?
Because no molecules have zero energy.
Why does the Maxwell-Boltzmann curve never touch the x-axis?
Because there is no maximum energy for molecules.
Where is the most probable energy on a Maxwell-Boltzmann distribution?
At the peak of the curve (Emp), not the same as the mean energy.
What happens to the Maxwell-Boltzmann distribution when temperature increases?
It flattens and shifts right, showing more molecules with energy > Ea.
How is rate of reaction defined?
Change in concentration of a substance per unit time.
What is the usual unit for rate of reaction?
mol dm⁻³ s⁻¹
What is the initial rate of a reaction?
The rate at the start of the reaction, where it is fastest.
How do you find rate from a concentration-time graph?
Draw a tangent and find its gradient.
What happens to rate when concentration or pressure increases?
There are more particles per volume, so more frequent effective collisions.
Does the energy distribution curve shape change with increased concentration?
No, the peak remains at the same energy.
How does increasing surface area affect reaction rate?
It increases the frequency of successful collisions.
What is a catalyst?
A substance that increases reaction rate without being used up.
How do catalysts work?
They provide an alternative reaction route with a lower activation energy.
What happens to particles at higher temperatures?
They move faster, collide more often, and more particles have energy > Ea.
How is rate measured in the thiosulfate and HCl reaction?
1/time taken for a cross under the reaction mixture to disappear.
Why can 1/time be used to measure rate in the sulfur formation reaction?
Because the amount of sulfur produced is fixed and constant.
How do rate-time curves differ for different concentrations?
Higher concentrations have steeper initial gradients.
What does a steeper gradient on a concentration-time graph indicate?
A faster reaction rate.
Why does doubling concentration double the rate?
Because it doubles the number of particles per volume and the frequency of effective collisions.
