How does particle size or surface area affect reaction rate?

Particle size or surface area directly affects the reaction rate; smaller particles or larger surface areas increase the reaction rate.

In chemical reactions, the rate of reaction is determined by the frequency and energy of successful collisions between reactant particles. The more collisions that occur, and the more energy these collisions have, the faster the reaction will proceed. This is where the size of the particles and the surface area come into play. To understand this further, you can explore the Basics of Collision Theory.

When a solid reactant is involved in a reaction, only the particles on the surface of the solid can collide with the particles of the other reactant. Therefore, the larger the surface area of the solid, the more particles are available for collisions, leading to an increased reaction rate. This principle is part of the broader Factors Affecting Rate of Reaction, which discusses how various physical and chemical conditions influence reaction speeds.

Similarly, the size of the particles also influences the reaction rate. Smaller particles have a larger surface area to volume ratio compared to larger particles. This means that a greater proportion of the particles are available on the surface for collisions, increasing the frequency of successful collisions and thus the reaction rate. This relationship between particle size, surface area, and reaction rates can be quantitatively analysed using Rate Equations.

For example, consider a sugar cube versus granulated sugar. If both are exposed to the same conditions, the granulated sugar will dissolve faster in water than the sugar cube. This is because the granulated sugar, being made up of smaller particles, has a larger surface area exposed to the water, leading to a faster reaction rate.

IB Chemistry Tutor Summary: In essence, the size of particles and their surface area play a key role in how fast a chemical reaction occurs. Smaller particles or those with larger surface areas enable more frequent and energetic collisions between reactants, speeding up the reaction. This is why substances in powder form react quicker than in lump form, as they offer more surface for collisions.