Quick questions on Collision theory and reaction rates: TCE Chemistry (Tasmania)

For a reaction to occur, particles must collide, but not every collision leads to reaction. A successful (effective) collision must satisfy two conditions:

At any temperature the particles in a sample have a spread of kinetic energies, shown by the Maxwell-Boltzmann distribution. Only the particles to the right of $E_a$ on this curve can react. Raising the temperature shifts the whole distribution to higher energies and, crucially, greatly increases the fraction of particles above $E_a$. This is why a modest temperature rise produces a large rate increase.

When you plot a measurable quantity (such as gas volume or mass) against time, the gradient of the tangent at any point gives the instantaneous rate at that moment. The steepest gradient is at the start, where reactant concentrations are highest, and the gradient falls to zero when the curve flattens and the reaction is complete. Comparing two runs is straightforward: a steeper initial gradient means a faster reaction, and a curve that levels off at the same final value but sooner indicates a faster rate with the same total amount of product. This lets you distinguish a change in rate (different gradient) from a change in amount of product (different final height).